6 The Chemistry Science Orbit - SARASWATI HOUSE Material/The Science... · adding chemical preservatives are used to preserve food. Chemistry in Agriculture: Explain to students how

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Teacher’s ManualScience OrbitThe Chemistry

(An imprint of New Saraswati House (India) Pvt. Ltd.)New Delhi-110002 (INDIA)

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(An imprint of New Saraswati House (India) Pvt. Ltd.)

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First published 2018

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The purpose of The Science Orbit series (3 to 8) teacher’s resource pack is to empower teachers to make classroom teaching a holistic experience. It will enable teachers to explain the chapters in the most effective way, which will not only impart knowledge, but also ignite interest in the minds of young learners towards the subject. A wide array of resources complement these manuals, which makes learning an interesting process instead of a routine chore.

Teacher’s Manual

Teacher’s Manual resources have been carefully prepared with an aim to make the process of teaching and learning interesting and intriguing for the teachers and learners alike. It comprises detailed lesson plans and answers to the coursebook along with solved worksheets and model test papers. These have been prepared keeping in mind the explanation of the concepts and the level appropriateness of the topics. Easily available teaching aids are used to make teaching and learning an interactive and lucid process. The lesson plans give a topic-wise explanation of each chapter. Its components are:

– Warm-up section guides the teacher to start the topic in an interesting way.

– Learning objectives give the list of measurable aims of each chapter, which should be achieved after teaching the chapter.

– Concept explanation gives a detailed method of explaining the important concepts of the chapter using various teaching aids.

– Reinforce section allows the teacher to check the progress of the concepts learned by the students with the help of textual questions and worksheets and allows them to revisit and revise the concepts, if required.

– Explore section helps the learners to do various activities, often taking them beyond their classroom learning.

App-based Digital Store

Digital offerings comprise digital resource embedded e-book, 2D and 3D animations, videos, interactive activities, slideshows, educational games, test generator and teacher’s manual.

Web Support

The web support consists of worksheets, model test papers, and answers to worksheets and model test papers. These would help teachers in assessing students on the concepts taught in the class.

Preface

Contents

1. Introduction to Chemistry 5

2. Elements, Compounds and Mixtures 15

3. Matter 26

Model Test Paper 1 36

4. Water 38

5. Air and Atmosphere 48

Model Test Paper 2 60

55

Learning Objectives

Students will be able to: understand the importance and role of chemistry in our lives and know about the

development of chemistry

know about eminent scientists and their inventions and contributions towards chemistry

understand the applications of chemistry in our day-to-day life: chemistry associated with food, industry, agriculture, cosmetics, clothing, medicines, glass, soaps and detergents

analyse how different chemical compounds are involved everywhere around us

1 Introduction to Chemistry

Warm-upMake an attempt to have an interactive class session by asking students what they know about early years — how people lived, what they ate, what they wore and where they lived?

Various changes occurred time to time in their food, clothing and shelter. All these changes occurred due to a branch of science called chemistry. Tell the students that people became more aware about their surroundings and more knowledgeable. Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation

Chemistry — meaning and importanceExplain to the students the meaning and importance of chemistry. Chemistry is everywhere in the world around us. The food we eat, the clothes we wear, the water we drink, the air we breathe, besides medicines,

fertilizers and insecticides are all related to chemistry.

Development of chemistry — a historical perspectiveExplain to the students chemistry has been around us since ancient time but its application was focused mainly on metallurgy. Later, scientists were successful to some extent in developing a process to extract metals and prepare alloys. They also used secret codes and symbols which later translated to the modern representation of elements and compounds by symbols and formulae. Robert William Boyle (1627–1691) was the fi rst chemist to perform experiments under controlled conditions and published his research with elaborate details of procedure, apparatus and observations. He is known as the ‘father of modern chemistry’.

Notable scientists/chemistsExplain to the students about the eminent

66

scientists and their contributions towards the fi eld of chemistry (refer table on page 12).

To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook.

Application of chemistry in our day-to-day lifeExplain to the students about the applications of chemistry. The life we are living today is all because of chemical inventions. Food and Chemistry: Explain to them that the food we eat contains nutrients which are all chemical compounds. Tell the students about various processes of food preservation which slows down food spoilage and ensures longer storage. In olden days, food items were preserved by sun drying, salting, smoking, fermentation and keeping them in sugar syrup. But now, modern techniques, such as canning, pasteurisation, freezing and adding chemical preservatives are used to preserve food. Chemistry in Agriculture: Explain to students how chemistry has helped to increase food production through fertilizers. They make the soil fertile by adding essential elements like nitrogen, potassium and phosphorus. A number of chemicals are used as pesticides and insecticides to protect crops. Cosmetics and Chemistry: Explain to the students how chemistry is associated with cosmetics also. Face powder, lipstick, nail polish, deodorants, perfumes, shampoos, body wash and face creams are all part of cosmetics and the essential ingredients of all the cosmetic products are chemical compounds. Tell the students that most foaming cosmetics, such as toothpaste, shower gel and shampoo, have sodium lauryl sulphate. Clothing and Chemistry: Explain to the students that during early times and stone

age, people covered their body with the bark of trees, big-sized leaves and animal skin or fur. Plant fibres, such as cotton, came into use after early man learnt about growing crops. Cotton, linen and flax are the fibres obtained from plants. Silk and wool are obtained from animals.

Tell the students today, many varieties of man-made fi bres are available and the credit goes to chemistry such as nylon – manufactured from adipic acid and hexamethylene diamine; terylene – manufactured from ethylene glycol and terphthalic acid; polyester – manufactured from benzene 1,4-dicarboxylic acid and an alcohol, ethane-1,2-diol, are some synthetic fibres. These days semi-synthetic fibres, such as terrycot, is also available which is a combination of terylene and cotton.

Chemicals as Medicines: Explain to the students that medicines are chemical substances used to cure, treat or prevent diseases. They are either obtained from plants and animals or prepared using chemicals. A class of compounds called alkaloids finds use in medicines and as intoxicants.

Tell them about the different categories of medicines.

• Antibiotics are the chemical substances produced by various species of microorganisms and other living systems; capable of inhibiting the growth of, or killing, bacteria and other microorganisms.

• Analgesics are chemicals that alleviate pain. Aspirin and paracetamol are commonly used analgesics.

• Antipyretics are chemicals that help to reduce fever. Paracetamol and aspirin are widely used antipyretics.

• Antiseptics such as tincture of iodine and phenols are chemicals used to

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prevent the growth of microorganisms on wounds and sores.

• Antacids are chemicals used to neutralise the excess acid produced in the stomach which cause burning sensation. Chemicals like milk of magnesia (gelusil) can neutralise the acid.

• Antihistamines are medicines that prevent or cure allergic reactions such as rashes and breathlessness. Examples are bilastine and certirizine.

To reinforce the concepts learnt before ask the students to do the related Pause and Do section from the textbook.

Chemicals in Industries: Explain to the students that chemistry has played a great role in Industries where naturally occurring raw material are converted into various products. Explain to them about the important chemical compounds like Plaster of Paris and cement.

Tell them that glass is another important chemical compound of varying utilities. Most glasses are silicates and not affected by chemicals. They can be moulded into any shape and prepared using limestone (CaCO3), soda ash (Na2CO3) and sand (SiO2). Make them aware of the different types of glasses and their uses.

Soaps and Detergents: Explain to the students that soap which they use regularly is also an important application from chemistry. Soaps are the sodium salts of fatty acids and detergents are the sodium salts of benzene sulphonic acid. Soap is a product which when used with water decreases surface tension, loosens unwanted particles and absorbs dirt and grease into foam which can be washed away. When soap solution comes in contact with dirt particles on the cloth, it forms a circular arrangement known as miscelles. When agitated, the miscelles

move away, carrying the dirt along with them.

Plastics: Explain to the students about the uses of plastic. The present age can rightly be called the plastic age. These days plastic is replacing metal and wood in every field. But the ill effects of plastic can also not be ignored. Plastics are non-biodegradable and can cause adverse health effects in the long run. Explain to them types of plastics with examples.

Paints, enamels and dyes: Explain to the students how chemistry is involved in paints also. The main ingredients in paints are oxides of zinc, magnesium and aluminium in suitable solvents. Enamel paint is a high-gloss oil based paint that is typically used on hard, non-porous surfaces such as metal, walls, etc.

Explain to the students that dyes are mostly used in the textile industry. Synthetic dyes are also used for colouring hair and skin.

Silicones: Make children aware about silicones which are a commercially important class of polymers that can be synthesised by the hydrolysis of suitably functionalised silicon derivatives.

Explain the various uses of silicones.

ReinforceTo reinforce, ask the students to read the Summary and Glossary sections and do the Exercises and Learning Zone from the textbook.

Help students develop skills (research and thinking) given in the Skills for Life section in the chapter.

Explore Ask the students to do Learn by Doing section given at the end of the chapter.

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Worksheet 1

1. Give two examples each of the following.

a. Sugar producing plants ___________________ ___________________

b. Natural fi bres ___________________ ___________________

c. Antipyretics ___________________ ___________________

d. Antibiotic penicillin ___________________ ___________________

e. Plastics ___________________ ___________________

2. Write the chemical formulae of the following.

a. Limestone _____________________________________________________

b. Plastic of Paris _____________________________________________________

c. Sand _____________________________________________________

d. Gypsum _____________________________________________________

3. What is a supercooled liquid? Name its two types.

________________________________________________________________________

________________________________________________________________________

4. What is pasteurisation?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

5. Give two uses of Plaster of Paris.

________________________________________________________________________

________________________________________________________________________

6. Give two examples of synthetic fi bres. Write their composition also.

________________________________________________________________________

________________________________________________________________________

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Worksheet 2

1. Name the concerned scientist.

a. Discovered neutrons ______________________________

b. Gave a enetic code of the cell ______________________________

c. Gave the basic idea of an element and ______________________________ compound

d. The coined laws of electrolysis ______________________________

e. Method to protect milk from spoilage ______________________________

f. Discovered penicillin ______________________________

2. Defi ne the following terms.

a. Thermosetting plastics

________________________________________________________________________

________________________________________________________________________

b. Alchemy

________________________________________________________________________

________________________________________________________________________

c. Pesticides

________________________________________________________________________

________________________________________________________________________

d. Food preservation

________________________________________________________________________

________________________________________________________________________

3. Why is coloured glass in demand these days?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

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Answers to Coursebook

PART 1

A 1 (d) 2. (d) 3. (b) 4. (c)

5. (c)

B 1. Sunscreens

2. Wool, silk

3. alkaloids

4. Neem, turmeric

5. POP

6. Laminated glass

C 1. True 2. True 3. False

4. False 5. False 6. True

D 1. Melathion 2. Glycerol

3. Carnauba wax 4. Lamp black

5. Sodium lauryl sulphate

PART 2

A 1. Hindi term for chemistry is ‘Rasasastra’. ‘Rasa’ means essence and ‘sastra’ means Science.

2. Sir Humphry Davy

3. Plastics are non-biodegradable and can cause adverse health effects in the long run.

4. The method in which processed food can be stored in air-tight containers for many days is called canning.

5. Benzoic acid, sodium benzoate

6. The raw materials used in agroindustries are agricultural products.

7. Moisturisers prevent water loss from the skin.

8. We should not wear synthetic clothes while cooking because they catch fi re easily. Also, they melt and stick to the body easily.

9. Antibiotics are chemical substances which are capable of inhibiting the growth of bacteria and other microorganisms.

These are produced by various species of microorganisms and other living system. Penicillin is one of the best-known antibiotics.

B 1. Modern methods of food preservation are – canning, pasteurisation, freezing and adding chemical preservatives.

2. Sugar, salt, tea and coffee

3. Dyes are natural or synthetic substances used to add colour to or change the colour of something. They are mostly used in the textile industry for colouring hair or skin.

4. Nylon, rayon, polyester and terylene

5. Advantages of synthetic fi bres–

• Synthetic fi bres are stronger than natural fi bres.

• They have longer life.

• They are easy to handle as they dry faster.

• They are wrinkle–resistant.

Disadvantages of synthetic fi bres–

• They melt easily and stick to the body.

• They catch fi re easily.

6. (a) Cement is used to manufacture lamp posts, telephone posts, railway sleepers.

(b) Cement is used in the construction of various structures like bridges, water tanks, tunnels etc.

7. Agro industries convert agricultural products into other products e.g. – paper industry, sugar industry, rubber industry, whereas mineral industries convert minerals such as coal and petroleum into many useful chemicals. They extract metals from their ores and manufacture automobiles and electrical equipments.

8. Soda glass or soda-lime glass, coloured glass, plate glass, safety glass, laminated glass or bullet proof glass, optical glass or

1111

fl int glass, pyrex glass, photo chromatic glass, lead crystal glass

C 1. Chemistry is a science that is very close to human life as well as non-living matters. Chemistry is a creative, analytical and logical science. Chemical reactions occur when we breathe, eat or just sit. Chemistry fi nds application in the fi elds of food, clothing, health and electrical devices. It has helped to invent medicines for diseases which were once regarded as incurable. Chemistry has helped in producing many varieties of synthetic materials.

2. Sugar is prepared from sugar cane juice using chemical processes, such as filtration, evaporation, decolourisation with animal charcoal, crystallisation and drying.

Salt is obtained from seawater. The processes involved are the evaporation of seawater, collecting the crude salt crystals, recrystallising and drying.

Vegetable oil is extracted from oilseeds by a process called steam distillation.

Coffee berries are dried, roasted, powdered and packed for marketing as coffee powder.

3. The essential ingredients of cosmetics are:

Thickeners - They enhance the stability and the overall performance of the cosmetic. Stearic acid, carnauba wax and gum are commonly used as thickeners. Mineral thickeners, such as silica gel and magnesium aluminium silicate, are used in some cosmetics. Moisturisers - prevent water loss from the skin. Beeswax, olive oil, glycerol and petroleum jelly are commonly used moisturisers.

Glimmers - give sparkling shine to the skin. Mica flakes mixed with titanium dioxide is a popular glimmer.

Sunscreens are creams that protect us from harmful sunrays. Titanium dioxide is found in almost every sunscreen. It blocks ultraviolet light and has a strong absorbing capacity. Titanium dioxide is also used in nail paints and lip colour.

4. Chemistry has helped to increase food production through fertilizers. Fertilizers are of three types: potash fertilizers which are rich in potassium, nitrogenous fertilizers which are rich in nitrogen and phosphatic fertilizers which supplement phosphorus. They make the soil fertile by adding essential elements to soil. A number of chemicals are used as pesticides and insecticides to protect crops. Malathion and copper sulphate are some common pesticides. Some commonly used insecticides are malathion and bordaux mixture.

5. • Matter is made up of indivisible particles called atoms.

• Atoms can neither be created nor destroyed.

• Atoms of the same elements are alike and the atoms of different elements are different.

• Atoms combine to form molecules.

• The atoms of different elements combine in whole number ratios to form compounds.

• Dalton’s theory paved the way for the advanced study of atoms.

6. Earlier natural fibres like cotton, linen, flax, silk and wool were used for making clothes. Cotton, linen and flax are obtained from plants. Silk and wool are obtained from animals - silkworms and sheep respectively. These days, because of chemistry, varieties of man-made fi bres or synthetic fi bres are present in the market. Nylon – manufactured from adipic acid and hexamethylene diamine; terylene – manufactured from ethylene glycol and terphthalic acid; are some synthetic fibres. These are woven into cloth or mixed with cotton, silk and wool to make mixed fibres before weaving. Clothes are woven in a loom. Rayon is a modified natural fibre. Sometimes, cellulose fi bres are chemically treated to increase their strength and luster.

1212

7. To prepare soap in the laboratory sodium hydroxide pellets, castor oil or coconut oil, salt, 250 ml beakers-2, a bunsen burner, glass rod for stirring, tripod stand and wire gauze are required. Take 100 mL of oil in a beaker and heat it to up to about 70 °C on the Bunsen burner. In the other beaker take 100 mL of water and add sodium hydroxide pellets in small quantities and stir. Go on adding the pellets till traces remain undissolved. Now add this solution to the hot oil while stirring. A pasty mass is obtained. Dissolve a tablespoon of salt in about 20 mL water and add it to the pasty mass. The soap separates out and floats on the top. It is then skimmed and pressed into a mould.

8. Silicones are a commercially important class of polymers that have high thermal stability and dielectric strength and can be synthesised by the hydrolysis of suitably functionalised silicon derivatives. Silicones are water repelling in nature.

Uses:

• They are used in many aspects of aircraft and spacecraft assembly and maintenance, as they can withstand high stress and temperature extremes.

• In building construction, silicone sealants, adhesives and coatings make construction materials work better and last longer.

• Bakeware and cookware are more sturdy, convenient, easy to use and long-lasting when made with silicone rubber.

• The flexible, non-stick surface is easy to clean and does not impart any flavour or odour to the food.

• Silicones are used in a wide range of car parts, including airbags, engine gaskets, headlamps, hydraulic bearings, ignition cables, radiator seals, shock absorbers,etc.

D 1. Antacids are chemicals used to neutralise the excess acid produced in the stomach.

Chemicals like milk of magnesia (gelusil) can neutralise the acid. Such chemicals are called antacids. Mint is a natural antacid used to treat indigestion.

2. Thermosetting plastics, when heated, melt and set into a hard mass, which cannot be melted again. These are used in making insulating handles for cooking utensils, such as pressure cooker and handles, and the body parts of electrical appliances. Examples of thermosetting plastics are bakelite and melamine.

3. Pyrex glass is highly heat resistant. Laboratory equipment and ovenware are made of pyrex glass.

4. Antipyretics are chemicals that help to reduce fever. Paracetamol and aspirin are widely used antipyretics.

5. Silicones are a commercially important class of polymers that have high thermal stability and dielectric strength and can be synthesised by the hydrolysis of suitably functionalised silicon derivatives. Silicones are water repelling in nature.

6. When small amounts of metallic oxides are mixed with a hot molten mixture of sand, sodium carbonate and limestone, we get coloured glass. The desired colour determines the choice of the metallic oxide to be added, as different metallic oxides give different colour to the glass.

E 1. Agro industries convert agricultural products into other products whereas mineral industries convert minerals such as coal, petroleum, etc. into many useful chemicals. Examples of agro industries are the paper industry, the sugar industry, the cotton and jute industry, the rubber industry, dairy farms, etc. Mineral industries also extract metals from their ores and manufacture automobiles, electronic goods, electrical equipment, etc.

2. Analgesics are chemicals that alleviate pain. Aspirin and paracetamol are commonly used analgesics. Antipyretics are chemicals that help to reduce fever. Paracetamol and aspirin are widely used antipyretics.

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3. Processed foods can be stored in airtight containers for many days. This process is called canning. Whereas refrigeration helps to keep vegetables, fruits, meat and milk products in fresh condition for over a week.

4. Laminated glass is also called bulletproof glass. It is stronger than safety glass. It is used in aeroplanes and in the windshields of cars. Safety glass is made by fusing a plastic sheet between two glass sheets while moulding the glass. It is also called shatterproof glass. The special quality of this glass is that in case the glass breaks, the broken pieces stick to the plastic and do not fly off. This type of glass is used in automobiles and making bulletproof screens.

5. Fertilizers increases the food production. They make the soil fertile by adding essential elements to soil. Plants can obtain nitrogen, potassium and phosphorus from these, whereas insecticides help to protect crops from insects. Some commonly used insecticides are malathion and bordaux mixture.

LEARNING ZONE

Picture based questions

1. (a) Plaster of Paris (POP)

(b) It is prepared by heating gypsum i.e. calcium sulphate dihydrate (CaSO4.2H2O) to 120 °C

Gypsum →heat to 120 °C Plaster of Paris

(c) When mixed with water, it sets to a hard mass and is thus used to make idols.

2. (a) First is—thermoplastic and the other is—thermosetting plastic.

Thermoplastic can be melted by heating plastic materials and moulding them into new objects again and again whereas thermosetting plastic when heated, melt and set into a hard mass, which cannot be melted again.

(b) Plastic of second variety is used to make the handles of cookware because

thermosetting plastic when heated, melt and set into a hard mass, which cannot be melted again.

3. (a) Soap solution comes in contact with dirt particles on the cloth

(b) One end of the long chain of the soap molecule attaches to the dirt and the other end is in contact with water.

(c) Several such molecules arrange in circular fashion around dirt or stain. This arrangement is called a miscelle. The miscelle entraps the dirt particles. When agitated, the miscelles move away, carrying the dirt along with them.

Think and answer

1. Antibiotics are chemical substances produced by various species of microorganisms and other living systems; they are capable of inhibiting the growth of, or killing, bacteria and other microorganisms. These organisms can be bacteria, viruses, fungi or protozoa.

Whereas vaccines are biological preparation that provides active acquired immunity to a particular disease. A vaccine typically contains an agent that resembles a disease – causing microorganism and is often made from weakened or killed forms of microbes.

2. Bacteria grow and breed on food best at room temperature. The coldness from the refrigerator slows down the growth of that bacteria and therefore food remains fresh for a long period and lasts longer.

3. Though fertilizers supply nutrients to the soil like potassium, phosphorus and nitrates, but they have negative effects on soil and environment. They affect the porosity and water holding capacity of the soil. During excess rains, water from agricultural fi elds is washed away into rivers along with soil containing fertilizers, thus polluting water. Also, certain fertilizers like phosphogypsum emit dangerous radiations into the ecosystem which causes various diseases. Thus, manure is preferred as it is a natural item and will increase the fertility of soil without the help of any chemical.

1414

4. It is not advisable to use non-stick pan for cooking because overheating of these pans causes their coating to breakdown, which can result in the release of surface particles or toxic gases. One of the chemicals which is harmful and used to make these pans is PFOA (per fl uorooctanoic acids), including Tefl on.

5. Plastic is replacing metal and wood in every field. Plastics have been important for distributing clean food and water, for medical devices, surgical gloves and affordable clothing. They’ve played a big role in health and sanitation. The fact that they don’t dissolve or decay is a plus for most of their intended uses.

Answers to WorksheetsWORKSHEET 1

1. a. Sugarcane, sugar beet

b. Cotton, silk

c. Paracetamol and aspirin

d. Ampicillin, penicillin G

e. Bakelite, melamine

2. a. CaCO3

b. CaSO4.½H2O – Calcium sulphate hemihydrates

c. SiO2

d. CaSO4.2H2O – Calcium sulphate dihydrate

3. Glass is known as supercooled liquid. It is a mixture having no defi nite boiling or freezing point. It is transparent and not affected by chemicals and mostly silicates.

4. Pasteurisation is a process of heat processing the food to kill pathogenic bacteria to make the food safe to eat.

5. it is used to make casts and moulds. It is used in surgical plasters.

6. Nylon – Manufactured from adipic acid and hexamethylene diamine.

Terylene – Manufactured from ethylene glycol and terphthalic acid.

WORKSHEET 2

1. a. Sir James Chadwick

b. Hargobind Khurana

c. Aristotle

d. Michael Faraday

e. Louis Pasteur

f. Alexander Flemming

2. a. Plastics that set on healing and cannot be remoulded on further heating. For example, bakelite.

b. A technique of converting one metal into another is called alchemy.

c. A group of chemicals that help to control the growth of pests such as rats, insects, fungi is called pesticides.

d. The process of treating and handling food to stop or slow down food spoilage and deterioration of quality, its nutritive values, thus allowing for longer storage, is called food preservation.

3. To make the coloured glass, small amounts of metallic oxides are mixed with a hot molten mixture of sand, sodium carbonate and limestone. Metallic oxide is used for the colour. It is used for decorating walls, making sunglasses and for making light signals for automobiles, trains and automobiles.

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Learning Objectives

Students will be able to: classify the elements as metals and non-metals

know characteristics of elements, compounds and mixtures

identify the differences between element, mixture and compound

understand the concept of atomicity and valency

write the symbols of elements and chemical formulae of compounds

identify physical methods of separating the mixtures from their impurities

2 Elements, Compounds and Mixtures

Warm-upDraw attention on the prior knowledge of children related to matter. Tell them to make a list of substances like lemonade, chalk piece, a cup of tea, cooked rice on a plate and wood. Now let them analyse whether these substances are made of single substances or two or more substances. Most of the substances around us are mixture of

two or more elements or compounds.

Now ask the students to complete the exercise given in the Warm-up section.

Concept ExplanationMatter and its classifi cationExplain to the students that anything that has weight and occupies space is called matter which can exist in different forms.

Pure substance Mixture

Matter

Element Compound Homogeneous mixture

Heterogeneous mixture

A pure substance has a defi nite composition and fixed chemical properties, fixed melting point, boiling point and density, for example elements and compounds

Explain to the students that element which is composed of only one kind of atom can be classified into metals and non-metals.

1616

Make them understand that metals which are solid at room temperature with the exception of mercury are lustrous, malleable, ductile, good conductors of heat and electricity, sonorous and have high melting and boiling point, e.g., Au, Pb, Ag, Cu. On the other hand, non-metals, which are generally solids and gases are non-lustrous, non-malleable, non-ductile, non-sonorous and do not conduct electricity(except graphite), e.g., C, H, O, N.

To reinforce the concept learnt before ask the students to do the related Pause and Do section given in the textbook.

Symbol of an ElementExplain to the students about the chemical symbol or an abbreviation used to represent an element. Sir John Dalton developed a set of pictorial symbols for some elements. Later modern system of representation of chemicals was given by different scientists who arranged elements using these symbols in a table called the modern periodic table. (Refer to Tables 2.1, 2.2, 2.3)


Compounds and MixturesExplain to the students the difference between compounds and mixtures. Compounds are pure substances formed by the chemical combination of two or more elements in a defi nite proportion (by mass).For example, water, marble, glucose, sugar, salt, alcohol, carbon dioxide, calcium oxide, nitrogen dioxide, zinc chloride, etc. Mixtures are made up of two or more pure substances (elements, compounds or both) that retain their individual properties. The components that make up a mixture are not chemically combined. Lemon juice is a mixture of lemon extract, sugar and water. (Refer table 2.8)

Explain to the students the concept of atomicity, valency and steps for writing chemical formula. The number of atoms present in a molecule of an element is called its atomicity whereas the combining capacity of the atom of an element is called its valency. Refer table 2.4, 2.6, 2.7

Separation of MixturesExplain to the students the need for separation of mixture into their constituent: to obtain useful constituents and to obtain pure substances. The method should be such that it should not affect the physical and chemical properties of the elements present in the mixture. Make them aware that in homogeneous mixtures, the components are mixed so well with each other that it is diffi cult to differentiate one from the other either by particle size or colour and also in heterogeneous mixtures, particles can be differentiated either by the colour, size or shape of the components.

Explain to the students various processes of separation of mixtures of solids like-

Handpicking: If the components can be differentiated by colour, size and shape and one of the components is less in quantity. For example, rice mixed with stones.

Sieving: This method is usually preferred when the components are of different sizes and one of the components is small enough to pass through the holes of a sieve. e.g., flour is separated from impurities through sieving.

Winnowing: Mixture is allowed to fall from a height in the form of a spray. The lighter particles fall far away while heavier grains fall near the person winnowing. Winnowing is done to separate husk from grains.

Magnetic separation: Magnetic compo-nents, such as scrap iron or other metals that get attracted to a magnet, can be easily

1717

separated from a heap of waste materials. For example, iron filings can be separated from an iron and sulphur mixture using a magnet.

Activity – Students can be shown in the class separation of pieces of stones in rice by handpicking and rice grains and salt by sieving.

Explain to the students about the separation of mixture of an insoluble solid and a liquid. The mixture is allowed to stand. The solid particles that settle down are known as sediments. The liquid above the sediment is called the supernatant. The clear supernatant liquid is poured into another container without disturbing the sediment known as decantation. If the solid particles do not settle down, they are separated by filtration. The liquid that passes through the filter is called the filtrate. The insoluble component that remains on the filter is called the residue.

Explain to the students the separation of mixture of a solid and a liquid where

the solid dissolves in the liquid. It involves evaporation and crystallisation. The process of changing a substance from its liquid state to its gaseous state at a temperature below its boiling point is evaporation. Salt is prepared from seawater using this method. In crystallisation, solution is first heated and concentrated solution is obtained which is then cooled. Solid comes out in the form of crystals.




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Worksheet 1

1. Identify the method of separation to be used to separate the following mixtures.

a. Unwanted grains from rice. ______________________________

b. Salt from sea water. ______________________________

c. Stones from sand at construction site. ______________________________

d. Grains from stalks. ______________________________

e. Lighter chaff particles from heavier grains. ______________________________

f. Oil from water. ______________________________

2. Lemonade is prepared by mixing lemon juice and sugar in water. When should ice be added to cool it?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

3. Complete the following table.

Name of compound Formula Elements present Number of atoms

Water H2O

Carbon Monoxide CO Carbon, Oxygen

Methane 1 atom carbon4 atoms hydrogen

Carbon Dioxide CO2

Sugar C6H12O6

Salt 1 atom Na1 atom Cl

Oxygen 2 atoms of oxygen

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Worksheet 2

1. Fill in the blanks.

a. Cream is separated from milk by _________.

b. Common salt is obtained from seawater by ___________.

c. The method used to settle down the suspended particles in muddy water is called ____________.

d. The number of atoms present in a molecule of an element is called its ____________.

e. A new substance formed when atoms combine in a fi xed ratio is _______________.

f. Mixture in which particles can be differentiated either by colour, size or shape of the components _______________.

f. The process of separation of impurities from pure substances is called ____________.

h. The smallest unit of a compound is _____________.

2. Give examples of:

a. Pure substances

________________________________________________________________________

b. Impure substances

________________________________________________________________________

3. Name the method to separate rice and salt.

________________________________________________________________________

________________________________________________________________________

4. Describe the method to obtain salt from seawater.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

5. Is it possible to separate sugar mixed with wheat fl our? If yes, how will you do it?

________________________________________________________________________

________________________________________________________________________

2020


PART 1

A 1 (c) 2. (a) 3. (d) 4. (a)

5. (b)

B 1. Non-metals 2. John Dalton

3. Homogeneous 4. Handpicking

5. Winnowing

C 1. False 2. True 3. True

4. True 5. True 6. True

D 1. Triatomic

2. Sieving

3. Atom

4. Valency

5. Sedimentation followed by decantation

6. Magnetic separation

PART 2

A 1. The formula of water is H2O. This means two atoms of hydrogen and one atom of oxygen combine to form water (i.e. 2:1).

2. An element is a pure substance which is composed of only one kind of atom which is a very small particle and cannot be broken down into simpler form by any physical or chemical means.

3. Common salt is sodium chloride – NaCl

4. MgCl2 – Magnesium chloride

5. (a) K

(b) Be

6. Homogeneous mixture is a mixture in which components are mixed so well with each other that it is diffi cult to differentiate one from the other, either by particle size or colour.

7. In the process of sedimentation, the liquid above the sediment is called supernatant which is then poured into another

container for decantation.

8. Alum helps the particles to settle down quickly in the process of sedimentation.

B 1. Mixture is made up of two or more pure substances. We can separate cream from milk by churning, so it is a mixture of cream and water.

2. The number of atoms present in one molecule of a compound are represented using the chemical symbols of its constituent elements, which is known as chemical formula. It is a way of expressing information about the proportion of atoms that constitute a particular chemical compound. For example, one molecule of water is represented as H2O which means one molecule of water contains 2 atoms of hydrogen and 1 atom of oxygen.

3. A solution of common salt in water is heated. The liquid evaporates, leaving the solid salt behind.

4. (a) Sieving

(b) Evaporation

(c) Separating funnel

(d) Magnetic separation

5. The sugar solution is first heated so that some liquid evaporates and we get a concentrated solution. This solution is then cooled. Solid comes out in the form of crystals.

6. If the number of atoms present in a molecule of an element is two, its atomicity is 2 and it is diatomic. For e.g. Oxygen (O2), Hydrogen (H2), Nitrogen (N2), Iodine (I2)

C. 1. Pure substances are defi ned as substances that are made of only one type of atoms or molecules. A pure substance has a fi xed melting point, boiling point and density. It has a fixed composition and fixed chemical

2121

properties. For example, a molecule of salt consists of one atom of sodium and one atom of chlorine.

2. Metals are solid at room temperature with the exception of mercury which is a liquid at room temperature.

Properties of metals-

Lusture (shiny): Metals such as gold and silver are used to make jewellery due to their shiny appearance.

Good conductor of heat and electricity: Metals such as iron and silver are used to make utensils since they are good conductors of heat. Copper and aluminium are used to make electrical cables, as they are good conductors of electricity.

Strength: Metals such as iron are used to build scaffolding and bridges, as they are strong.

Sonorous: Metals make a deep, ringing sound when struck, hence, they are used to make bells and musical instruments.

Ductile (can be stretched to make thin wires): Metals like copper and nickel can be stretched into thin wires.

Malleable (can be hammered or pressed into shape without breaking): Metals are used to make boxes and almirahs as they can be beaten into thin sheets.

High boiling and melting points: For example, tungsten and molybdenum are considered as building material at power plants because of their exceptionally high melting point, which allows enormous heat resistance.

3. Step 1: Write the symbols of the elements present in the compound.

Step 2: Write the valencies of the constituent elements below them

Step 3: Cross over or swap the valencies of these elements and write them with the elements as subscripts.

Step 4: If the valency can be simplified, divide both the valencies with the smallest valency of the element. If the valency of any element is 1, it cannot be simplified further. Then, write the formula of the compound.

Formula of potassium oxide-

Step 1 Symbol K O

Step 2 Valency 1 2

Step 3 Swap 2 1

Formula K2O

4. A symbol or an abbreviation is used to represent an element. It is very inconvenient to refer to elements and their compounds using their full name, so the practice of using symbols for elements or compounds was started. Symbols in the periodic table increases scientifi c communication across the world. Each element is represented by a chemical symbol to make the study easy and less time consuming.

5. A mixture is made up of two or more pure substances (elements, compounds or both) that retain their individual properties. The components that make up a mixture are not chemically combined. Lemon juice is a mixture of lemon extract, sugar and water.

Mixtures are of two types: homogeneous and heterogeneous.

Homogeneous mixtures: In this type of mixtures, the components are mixed so well with each other that it is diffi cult to differentiate one from the other either by particle size or colour. Lemon juice contains water, lemon extract and sugar. But by looking at it, we cannot identify which is what and we see only one entity.

Heterogeneous mixtures: In this type of mixture particles can be differentiated either by the colour, size or shape of the components. A mixture of sand and salt can be differentiated by colour. Chalk

2222

powder and water: In a mixture of chalk powder and water, the solid phase and the liquid phase are distinctly visible.

6. (a) Iron fi ling can be separated from sand and iodine by magnetic separation. Now, mixture of sand and iodine is heated; iodine will turn into gas and leave the sand behind.

(b) Chalk powder can be separated from the husk and grains by sievering. Now, the mixture is allowed to fall from a height in the form of a spray. The lighter particles (husk) fall far away while heavier grains fall near the person winnowing.

(c) Add water to the sand and salt mixture. The salt dissolves in water. Separate the sand from water by decantation followed by fi lteration. Marble can be collected now using evaporation. Common salt is separated.

(d) Salt dissolves in water and pebbles will settle down and separate them by sedimentation followed by decantation. To get salt back, evaporate the solution.

D 1. Sedimentation is the process to separate an insoluble solid from a liquid and the following steps are followed: The mixture is allowed to stand and the solid particles settle down. If the solid particles do not settle quickly, a crystal of alum is added which helps the particles to settle down quickly. This technique is called loading. The component that settles down is called is called the sediment. The liquid above the sediment is called the supernatant.

2. Decantation is a process for the separation of mixtures, by removing a layer of liquid, generally one from which a sediment/precipitate has settled.

3. If the solid particles do not settle down, they are separated by filteration. In this process the funnel containing the filter paper is inserted in a conical flask. The suspension of the solid in the liquid is

poured into the funnel. The liquid passes through and the solid is retained on the filter paper. The liquid that passes through the filter is called the filtrate. The insoluble component that remains on the filter is called the residue.

4. The solution is first heated so that some liquid evaporates and we get a concentrated solution. This solution is then cooled and the solid comes out in the form of crystals.

5. The process in which solid turns into a gas without fi rst becoming liquid is known as sublimation. For e.g., when the surface layer of snow (dry ice) turns into fog without melting.

6. If a small crystal obtained in the process of crystallisation is suspended in the concentrated solution, solid particles attach themselves to the crystal and it grows bigger. This is called seeding. This method is used to purify solids. For example, salt prepared from seawater is purified using this method.

7. The mixture of insoluble solid and liquid is allowed to stand so that the solid particles settle down. If the solid particles do not settle quickly, a crystal of alum is added. It helps the particles to settle down quickly. This is called loading.

E 1. Sieving is usually preferred when the components are of different sizes and one of the components is small enough to pass through the holes of a sieve. The larger particles remain on the sieve while the smaller particles pass through. For example, flour is separated from impurities through sieving, whereas the mixture can be separated by handpicking if the components can be differentiated by colour, size and shape and one of the components is less in quantity. For example, rice mixed with stones or pulses containing clay particles can be separated by handpicking.

2323

3. A mixture is made up of two or more pure substances (elements, compounds or both) that retain their individual properties. The components that make up a mixture are not chemically combined. In a mixture, the components are present in any proportion. Compounds are pure substances formed by the chemical combination of two or more elements in a definite proportion (by mass). The properties of a compound differ from those of its constituent elements.

4. In homogeneous mixtures, the components are mixed so well with each other that we cannot differentiate one from the other either by particle size or colour. Lemon juice contains water, lemon extract and sugar. But by looking at it, we cannot identify them. We see only one entity, whereas in heterogeneous mixtures, particles can be differentiated either by the colour, size or shape of the components. A mixture of sand and salt can be differentiated by colour.

5. Sedimentation is the process in which the mixture with impurities is allowed to stand. The solid particles settle down. The component that settles down is called the sediment. The liquid above the sediment is called the supernatant. In the case of fi ltration, the solid particles do not settle down, are separated. The funnel containing the filter paper is inserted in a conical flask. The suspension of the solid in the liquid is poured into the funnel. The liquid passes through and the solid is retained on the filter paper. The liquid that passes through the filter is called the filtrate and the insoluble component that remains on the filter is called the residue.

6. The number of atoms present in a molecule of an element is called its atomicity. The combining capacity of the atom of an element is called its valency. The valency of an element is a whole number and varies from 1 to 8.

F Charcoal Mixture

Coconut Oil Mixture/compound

Kerosene Mixture

Milk Mixture

Carbon dioxide Compound

Iron Element

Nitrogen Element

Sulphur Element

Ammonia Compound

Sweets Mixture

Glucose Compound

Coal gas Mixture

Alcohol Compound

LEARNING ZONE


1. (a) Sieving

(b) This method is used when the components are of different sizes and one of the components is small enough to pass through the holes of a sieve.

2. (a)

(b)

(c) c

(d)

2. Metals Non-metals

1. These are solids at room temperature except mercury.

These are solids and gases at room temperature except bromine.

2. These are very hard except sodium. These are soft except diamond.

3. These are malleable and ductile. These are brittle and can be breakdown into piece.

4. These are shiny. these are non-lustrous except iodine.

2424

3. (a) Filtration

(b) If in a mixture, the solid particles do not settle down, they are separated by filtration.

(c) Rice flour and water

Think and answer

1. At normal room temperature, water is a liquid whereas its two elements hydrogen and oxygen are both gases. Water is used to put out fi res whereas hydrogen easily catches fi re.

2. 2H means two separate hydrogen atoms whereas H2 means a hydrogen molecule in which two hydrogen atoms bond together.

3. Water is heated until it boils and turns to steam. The boiling action kills the various bacteria and other pathogens, and as the steam rises it leaves behind waste material, minerals, heavy metals and other heavier contaminants. The steam is then cooled and returns to water.

Answers to Worksheets

WORKSHEET 1

1. (a) Handpicking

(b) Evaporation

(c) Sieving

(d) Winnowing

(e) Winnowing

(f) decantation

2. We should add ice after dissolving sugar. When the temperature is high, more sugar can be dissolved.

3. Name of compound Formula Elements present Number of atoms

Water H2O Hydrogen, Oxygen 2 atoms of hydrogen1 atom of oxygen

Carbon monoxide CO Carbon, Oxygen 1 atom of carbon1 atom of oxygen

Methane CH4 Carbon, Hydrogen 1 atom carbon4 atoms hydrogen

Carbon dioxide CO2 Carbon, Oxygen 1 atom carbon2 atoms oxygen

Sugar C6H12O6 Carbon, Hydrogen, Oxygen

6 atoms carbon12 atoms hydrogen6 atoms oxygen

Salt NaCl Sodium, Chlorine 1 atom Na1 atom Cl

Oxygen O2 Oxygen 2 atoms of oxygen

2525

WORKSHEET 2

1. a. Churning

b. Evaporation

c. Sedimentation and decantation

d. Atomicity

e. Compound

f. Heterogenous mixture

g. Purifi cation

h. Molecule

2. a. Iron, copper

b. Salt solution, air

3. Sieving

4. Sea water contains many salts mixed in it. One of them is common salt. When sea water is allowed to stand in shallow pits, water gets evaporated by sunlight and slowly turns into water vapour. In a few days, the water evaporates completely leaving behind the solid salts. Common salt is then obtained from this mixture of salts by further purifi cation.

5. Sugar can be separated from wheat fl our by sieving. Due to difference in the size of the particles, sugar will stay on sieve and wheat fl our will pass through it.

2626

Learning Objectives

Students will be able to: understand the concept of matter and molecules - the building blocks of matter

differentiate between three different states of matter – solid, liquid and gas

understand the interconversion of matter from one form to another

appreciate the factors responsible for different states of matter

understand the effect of heat on matter

analyse the difference between physical and chemical change

3 Matter

Warm-upStart the lesson by asking about things around them. Make an attempt to have an interactive session by asking the students questions like what do trees, air, water, have in common. Let them answer that all of these occupy space and have mass. All of them are made up of matter. It includes all substances of which the universe is made up of. Give them some clues of what all is matter and what is not matter. Feelings of love or sadness do not occupy space and do not have any mass. They are not matter. Now, ask the students to complete the exercise given in the Warm-up section.

Concept Explanation

Matter, its state and interconversion of states of mattersExplain to the students that matter is anything that occupies space and has mass. Matter exists in three states - solid, liquid and gas which can change from one form to another due to change in temperature. The processes

involved in interconversion are melting, evaporation, condensation and freezing.


Factors Responsible for Different States of MatterTell students that the particles that makeup matter are in a continual state of motion and responsible for different states of matter. These include intermolecular space/interparticle space, intermolecular force, Brownian movement.

Effect of Heat on MatterExplain to the students the effect of heat on different states of matter. Tell them that the random movement of the particles of a matter increases when it is heated. This could lead to a change in temperature or a change in the state of the matter. In solids, there are strong forces between the particles, so the amount of energy needed is more. In liquids, the intermolecular force is not as strong as that in

2727

solids and the molecules gain kinetic energy to move farther, thereby increasing the volume. Explain to the students that the force between the molecules of gases is negligible and on heating, these molecules move away from each other very fast, occupying the entire space available.

Physical and Chemical ChangesExplain to the students the concept of physical change or reversible change and chemical change or irreversible change.

Solids: Explain to the students that solids have a defi nite shape and a defi nite volume. Intermolecular space is almost absent and force of attraction between molecules is very strong. Solids can be rigid or fl exible, hard or soft, compressible or non-compressible. The molecules are very tightly packed.

Liquid: Explain to the students that liquids have a fi xed volume but do not have a fi xed volume. The molecules are less tightly packed and so can move around within the liquid. They take the shape of the container into which they are poured and force of attraction between molecules is not as strong as solids. Liquids are known as fl uids as they can fl ow.

Activity – Take different containers such as a transparent cup, a glass tumbler, a glass bowl, an empty water bottle. Pour water into these containers, the shape of water changes and there is no change in the volume of water when poured into different containers.

Gas: Explain to the students that gases do not have a defi nite shape or a defi nite volume. In gases, the molecules are so far apart that there is hardly any attraction between them. So they move around in the full space available to them.

Activity – Take a spoonful of iodine

crystals in the test tube and heat it over the spirit lamp. The iodine vapours fill the test tube and also continue to rise and come out of the test tube and spread out. This shows that gas cannot be confined to a container. It occupies the entire space available.

Explain to the students about physical and chemical change

Physical changes are reversible changes. Matter doesn’t undergo any change in composition, so original substance can be brought back. For example, melting of wax


Chemical changes are irreversible as new substance is formed. Original substance undergoes change in composition, so cannot be obtained back. For example, respiration

Also tell students to look around in their house and fi nd out different types of physical and chemical changes. Make students understand the change of one state of matter to another by process such as melting, boiling, condensation, freezing.

Make children aware of the fact that the process by which a solid substance changes into a vapour without passing through the liquid state is called sublimation.




2828

Worksheet 1

1. Observe the molecular arrangement and answer the following questions.

a. Identify the state of matter.

________________________________________________________________________

b. Write about the shape and volume of the matter.

________________________________________________________________________

c. Why do molecules fi ll up the space available to them?

________________________________________________________________________

2. Name the following.

a. State of matter that has no fi xed shape but fi xed volume ____________.

b. Basic building blocks of matter ____________.

c. Process of change in state of matter from a gas to a liquid ____________.

d. Dry ice ____________.

e. Process by which a solid changes into a vapour without passing through the liquid state ____________.

f. Zig-zag moment of tiny microscopic particles suspended in fl uids ____________.

3. Classify the following changes into physical or chemical.

a. Melting of wax _____________________

b. Boiling of rice _____________________

c. Burning of fuel _____________________

d. Formation of rust _____________________

2929

Worksheet 2

1. What happens when sugar is heated?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

2. Sponge is a solid, yet we are able to compress it. Why?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

3. Why is the smell of the perfume of incense stick fi lled in the whole room in few minutes, when lighted?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

4. Why does a gas exert pressure on the walls of a container?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

5. Why does a blacksmith heat the metal rim to fi x it on a cart wheel?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

3030

Answers to CoursebookPART 1

A 1 (b) 2. (b) 3. (c) 4. (d) 5. (b)

B 1. physical 2. chemical

3. melting point 4. closely

5. volume 6. freezing

C 1. false 2. true 3. false

4. true 5. true 6. true

D 1. Freezing

2. Melting 3. Condensation

4. Evaporation/boiling 5. Sublimation

PART 2

A 1. Solids have defi nite shape whereas liquids and gases do not have defi nite shape.

2. In metals, atoms are bound together and can easily move apart if they gain energy. So metals expand on heating.

3. Fluids are substances that can fl ow. It includes liquid and gas.

4. 0 °C

5. When a solid, for example sugar, is dissolved in water, the sugar molecules take the inter molecular spaces present between water molecules(liquid),thus keeping the level of water as such.

B 1. Evaporation occurs at all temperatures. It

is a spontaneous process whereas boiling occurs only at a specific temperature and this temperature is called the boiling point.

2. Refer Table 3.1, Page 55

3. When water is heated to 100°C, it changes to steam. The process of condensation of water vapour brings back water.

4. (a) Solids have a fi xed shape whereas liquids and gases do not have a fi xed shape.

(b) Solids and liquids have a fi xed volume, whereas gases do not have a fi xed volume.

(c) Liquids and gases fl ow but solids do not fl ow.

(d) Solids may be compressible or non-compressible. Liquids are slightly compressible whereas gases are highly compressible.

(e) In solids, molecules are closely packed. In liquids, molecules are not so closely packed. In gases, molecules are arranged far away.

(f) In solids, intermolecular forces are very strong. In liquids, intermolecular force are not so strong. In gases, they are negligible.

5. Refer - Part 1 Part B Answer-1

Solid Liquid Gas

Shape Defi nite shape No defi nite shape, they take the shape of the container in which they pour.

No defi nite shape

Volume Defi nite volume Defi nite volume No defi nite volume

Mobility Low mobility because of strong inter molecular forces between molecules

Flows easily Move around freely

Compressibility Compressible/Non-compressible

Diffi cult to compress Easy to compress

Arrangement of molecules

Closely packed with no intermolecular space

Molecules are loosely packed

Very loosely packed

Intermolecular forces

Strong; holds the molecules together

Less than solids Negligible

3131

C 1. Refer Fig. 3.4.

2. Solids other than metals do not expand on heating. In metals, atoms are bound together. Heating leads to a change in temperature or a change in the state of the matter. The change of state of matter is a physical change. When ice is heated, it changes into the liquid form and then due to further heating, it changes from liquid to steam or water vapour.

3. Molecules of gases are not bound by any kind of force. The heat supplied is solely used to increase the kinetic energy of the molecules and these molecules move away from each other very fast, occupying the entire space available. Thus, gases expand much more than liquids.

4. Melting of wax is a physical change as it can be converted back into solid form by cooling but in burning of candle the wax tends to convert into smoke which is a chemical change and cannot be converted back to original substance.

5. Chemical changes-

- ripening of fruit

- combustion of wood

- digestion of food

- photosynthesis

- respiration

Physical changes-

- Melting of ice cube

- Stretching of rubber band

- Water cycle in nature

- Wilting of leaves

- Manufacture of gold jewellery

6. The random movement of the particles of a matter increases when it is heated. This could lead to a change in temperature or a change in the state of the matter. The state of a matter changes when the arrangement of particles is changed. The change of state of matter is a physical change. Matter doesn’t undergo any change in composition. The

original substance can be brought back by reversing the conditions. The change is reversible.

D 1. Process in which a solid on heating changes into a liquid is called melting.

The melting point of ice is 0°C. The melting point of wax is 55 °C.

2. The process by which a solid substance changes into a vapour without passing through the liquid state is called sublimation.

3. The space present between the particles of matter is called the inter particle space. The gaseous state has the maximum inter particle space and it decreases from liquid to solid.

4. The force of attraction or repulsion that exists between particles is called the inter particle force. Force of attraction between molecules is maximum in the case of solids.

5. The particles in fluids keep moving rapidly in any direction and bombard each other. The zig-zag movement of tiny microscopic particles suspended in fluids is called Brownian movement.

E 1. Atoms are basic building blocks of matter. Combination of these atoms form molecules. A molecule is formed when two or more atoms join together chemically. Molecules are also the smallest particles of matter that can exist independently.

2. Solids have a definite shape and a definite volume. They retain their shape. They change shape only when an external agent, such as heat or force, acts on them. Solids can be rigid or fl exible, hard or soft, compressible or non-compressible, light or heavy. Liquids have a defi nite volume. They take the shape of the container into which they are poured. Liquids flow, hence, they are called fluids. Molecules in liquids are loosely packed and force of attraction between molecules is weak.

3. Liquids have a fixed volume but no fi xed shape. Molecules are loosely packed with

3232

weak force of attraction between them.

Gases do not have a definite shape or a defi nite volume. They cannot be confined to an open container. Most gases cannot be seen with the naked eye. Gas molecules are very loosely packed with negligible force of attraction between them.

4. The process by which a solid substance changes into a vapour without passing through the liquid state is called sublimation. On the other hand, evaporation is the change of state from liquid to gas. It is a spontaneous process.

5. Expansion occurs when the temperature of a substance increases and the molecules start moving at a fast speed, whereas when the temperature decreases in a substance, the speed of molecules also decreases and the size of object decreases.

LEARNING ZONE


1. a. Brownian movement.

b. Robert Brown

c. The particles keep moving rapidly in any direction and thus form the zig-zag movement.

2. Solid

Solid

Bottle - Solid Perfume - Liquid

Bottle - Solid Ink - Liquid

Samosa - Solid Vapour - Gas

Incense stick - Solid Fumes - Gas

Solid

3. cloud(vapour) to liquid----condensation

liquid to ice----freezing

ice to liquid----melting

ice to vapour----sublimation

Thinks and answer

1. A gas cylinder cannot be half fi lled because the particles of gas have less force of attraction and occupies the whole space given to them. Even if we try to half fi ll a gas cylinder it occupies the whole space given to them. This is why a gas cylinder cannot be half fi lled.

2. When we sweat, liquid water is produced on the surface of our skin. When this water evaporates, it reduces the skin temperature.

By blowing air around, the fan makes it easier for the air to evaporate sweat from our skin, which is how we eliminate body heat. The more evaporation, the cooler you feel.

3333

Answers to Assessment 1

A. 1. (a) 2. antipyretics 3. (a)

4. (c) 5. (a)

B. 1. Enamel paint is a high-gloss oil based paint that is typically used on hard, non-porous surfaces such as metal and walls.

2. A food that has been altered in some way during during preparation is called processed food. Food processing can be done by freezing, canning, baking and drying. Processed food can be stored in airtight containers for many days.

3. Plaster of Paris is calcium sulphate hemihydrate (CaSO4.1/2H2O). It is manufactured by heating calcium sulphate dihydrate (CaSO4.2H2O) to 120 °C. It is also called gypsum.

4. The number of atoms present in a molecule of an element is called its atomicity. Depending upon atomicity, molecules can be monatomic (1), diatomic (2), triatomic (3) or tetraatomic (4).

5. The combining capacity of the atom of an element is called its valency. The valency of an element is a whole number. An element with a valency of 1 is said to be monovalent; with a valency of 2, divalent and so on.

C. 1. helps in loading

2. oxides of zinc

3. water repelling in nature

4. sodium salts of fatty acids

5. supercooled liquid

D. 1. Aspirin

2. Thermoplastic

3. Atom

4. Atomicity

5. Penicillin

E. 1. Antipyretics are chemicals that help to reduce fever whereas antiseptics are

chemicals used to prevent the growth of microorganisms on wounds and sores. Paracetamol and aspirin are widely used antipyretics. Tincture of iodine and phenols are antiseptics.

2. Plaster of Paris (POP) is manufactured by heating calcium sulphate dihydrate (CaSO4.2H2O) to 120 °C whereas cement is manufactured by heating a mixture of gypsum, limestone and clay in a rotary kiln. POP is used in casting statues, surgical plasters, etc. whereas cement is used widely for the construction of various structures.

3. In the process of fi ltration, the suspension of the solid in the liquid is poured into the funnel. The liquid passes through and the solid is retained on the filter paper. The liquid that passes through the filter is called the filtrate. The insoluble component that remains on the filter is called the residue.

4. Refrigeration helps to keep vegetables, fruits, meat and milk products in fresh condition for over a week whereas canning is a method of preserving food in which food contents are processed and sealed in an airtight container.

F. 1. true 2. true 3. false

4. true 5. false

G. 1. The process of treating and handling food to stop or slow down food spoilage and the deterioration of quality, edibility or nutritive value, thus allowing for longer storage, is called food preservation.

2. Chemistry has played an important role in agriculture. It has helped to increase food production through fertilizers. They make the soil fertile by adding essential elements to soil. Plants can obtain nitrogen, potassium and phosphorus from these. Also number of chemicals are used as pesticides and insecticides to protect crops.

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3. (a) Sunscreens are creams that protect us from harmful sunrays. Titanium dioxide is found in almost every sunscreen. It blocks ultraviolet light and has a strong absorbing capacity.

(b) Moisturisers prevent water loss from the skin. Beeswax, olive oil, glycerol and petroleum jelly are commonly used moisturisers.

4. Lusture (shiny): Metals such as gold and silver are used to make jewellery due to their shiny appearance.

Good conductor of heat and electricity: used to make utensils and electric cables.

5. A mixture is made up of two or more pure substances (elements, compounds or both) that retain their individual properties and the components that make up a mixture are not chemically combined.

For example, lemon juice is a mixture of lemon extract, sugar and water. Air is a mixture of different gases.

6. If the number of atoms present in a molecule of an element is two,then it is called diatomic. Oxygen (O2), Hydrogen (H2), Nitrogen (N2) are the examples of diatomic elements.


Step 2: Write the valencies of the constituent elements below them.


Step 4: If the valency can be simplified, divide both the valencies with the smallest valency of the element. Then, write the formula of the compound.

H. 1. In sedimentation, the mixture is allowed to stand. The solid particles settle down. If the solid particles do not settle quickly, a crystal of alum is added. It helps the particles to settle down quickly. This technique is called loading. The component that settles down is called the

sediment. The liquid above the sediment is called the supernatant. In decantation the clear supernatant liquid is poured into another container without disturbing the sediment. This is called decantation.

2. In a mixture, the components are present in any proportion.

The components retain their properties.

A mixture does not have specific boiling and melting point or a characteristic colour, smell or taste.

Components can be separated by easy physical means.

3. Plastic is a synthetic material made from a wide range of organic polymers such as polythene, PVC, nylon etc. that can be moulded into shape. Plastics are non biodegradable and can cause adverse health e�ects in the long run. Plastics are of two types–thermoplastic and thermosetting plastic. Thermoplastic can be melted by heating plastic materials and moulding them into new objects again and again. Examples are PVC, poly ethylene (polythene), nylon, terylene, etc. Thermosetting plastics, when heated, melt and set into a hard mass, which cannot be melted again. These are used in making insulating handles for cooking utensils, such as pressure cooker and handles, and the body parts of electrical appliances. Examples of thermosetting plastics are bakelite and melamine.

4. The magnetic substances can be separated from a mixture by a process known as magnetic separation by the use of a magnet. Using this method, magnetic components get attracted toward a magnet and can be easily separated from a heap of waste materials. For example, iron filings can be separated from an iron and sulphur mixture using a magnet.

5. The theory proposed by John Dalton states that-

• Matter is made up of indivisible particles called atoms.

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• Atoms can neither be created nor destroyed.

• The atoms of the same elements are alike and the atoms of different elements are di�erent.

• Atoms combine to form molecules.

• The atoms of different elements combine in whole number ratios to

form compounds.

Picture based questions:

I. 1. Sedimentaton, decantation,fi ltration

2. Refer fi gure 2.10, 2.11, 2.12 chapter 2.

3. A mixture of sand and water, chalk powder and water are separated using these methods.


WORKSHEET 1

1. a. Gas

b. No fi xed shape or volume

c. Intermolecular attraction in gases is negligible. The Brownian movement is the fastest in gases, so molecules can spread over the entire space available.

2. a. Liquid

b. Molecules

c. Condensation

d. Solid carbon dioxide

e. Sublimation

f. Brownian movement

3. a. Physical

b. Chemical

c. Chemical

d. Chemical

WORKSHEET 2

1. When sugar is heated continuously then a black powdery substance is formed. This is a chemical change.

2. Sponge has very small holes throughout its structure. These holes are fi lled with air. When it is compressed, the air in the holes is squeezed out. Thus, we are able to compress it.

3. When the incense stick is lighted, the heat energy makes the particles of the perfume to move rapidly. Thus, they easily drift through the air in the room and hence we can smell it anywhere in the room.

4. The molecules of a gas have very large kinetic energy. When these molecules strike against the walls of containing vessel, they exert certain average force per unit area. As the force per unit area is known as pressure, therefore, the gases exert pressure on the sides of the containing vessel.

5. A metal rim is made slightly smaller. Blacksmith heats the metal rim to fi x it onto a cart wheel because on heating, the rim expands and fi ts onto the wheel. Then on cooling, the rim contracts and fi ts tightly onto the wheel.

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Total marks: 50Time: 3 hours

Model Test Paper 1

Section AA. Fill in the blanks. (5 × 1=5)

1. Hydrogen in Latin means _____________ .

2. The symbol of gold is _____________ .

3. Non-metals are _____________ and _____________ at room temperature.

4. Two or more atoms combine to form a _____________ .

5. The insoluble component that remains on the fi lter is called the _____________ .

B. Multiple choice questions. (5 × 1=5)

1. The non-metal which conducts electricity

a. nitrogen b. graphite c. bromine d. sulphur

2. The atomicity of oxygen is:

a. 1 b. 3 c. 2 d. 0

3. The movement of the particles of a matter _________ when it is heated.

a. decreases b. increases

c. remains the same d. increases fi rst and then decreases

4. Antipyretics are medicines that

a. reduce fever b. prevent growth of microorganisms

c. help to increase vision d. increases iron in the body

5. A homogeneous mixture of two or more metals is called _________

a. alloy b. soap c. plastic d. antibiotics

C. State whether true or false. (5 × 1=5)

1. Salts of iron, aluminium and chromium are used to make dyes.

2. Synthetic fi bres are stronger than natural fi bres and so they last longer.

3. Pectin powder is used to preserve fruits and vegetables.

4. Pure substance has no fi xed composition and chemical properties.

5. Phosphorus is an example of tetra atomic molecule.

D. Name the following. (4 × 1=4)

1. The only non-metal that exists as a liquid at normal temperature _____________

2. Sodium salts of fatty acids _____________

3. The temperature at which a solid changes into a liquid _____________

4. Adding a substance to a suspension so that solid particles settle down quickly _____________

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Section BA. Defi ne the following. (3 × 1=3)

1. Homogenous mixture

2. Food preservation

3. Matter

B. Short Answer Questions. (4 × 3=12)

1. Differentiate between solids and gases on the basis of shape, volume and intermolecular forces.

2. Differentiate between physical change and chemical change.

3. What are mixtures? Give 4 examples.

4. Why do gases expand on heating.

C. Long Answer questions. (4 x4=16)

1. What are non-metals? Give 4 examples. How do they differ from metals on the basis of boiling and melting point and luster?

2. A thick coating of paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed? Explain the type of change.

3. Write the formula of carbon di sulphide. Explain the steps to write chemical formula of above compound.

4. a. Name the process of separation.

b. When is this process done.

c. Explain the process.

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Learning Objectives

Students will be able to: learn about sources of water – rainwater, surface water, groundwater

understand water cycle

know how we get water in the taps at home.

Know about mineral water.

understand the concept of solute, solvent and a solution

learn about types of solution

understand solubility and effect of temperature on solubility

understand water pollution and reasons for water pollution

know what changes can be made to reduce water pollution

appriciate the method of water conservation

4 Water

Warm-upAsk the students about the most common and important substance for survival of life after air which covers three–fourths of the earth’s surface. Water is not evenly spread on the earth — there may be fl oods at some places and drought at other places. It is called a universal solvent as it dissolves many compounds in it. Ask them to make a list of activities in which they use water during the whole day.

Now, ask the students to complete the exercise given in the Warm-up section.

Concept ExplanationImportance of waterExplain to the students that water is one of the most important requirements for life. All living things need water for survival.

Plants need water for photosynthesis and medium of transport for minerals and other nutrients between different parts of plants.

Human beings need water for drinking, cooking and washing purposes.

Tell them about other uses of water.


Sources of WaterExplain to the students about different sources of water. Rainwater being the primary source of water, which is free from germs and solid impurities. All surface water bodies like oceans, seas, rivers and lakes get water from rain and form surface water. Also rainwater that percolates down the ground is called groundwater. For example,

3939

wells, hand pumps and springs. The level of groundwater is called water table. Tell them overuse of groundwater is causing the water table in cities and towns to go down which is a cause of worry.

Explain to the students the reasons how rivers are drying up – mainly due to unauthorised constructions and quarrying of sand, which is resulting in shortage of water.

Water CycleExplain the students about the three states in which water exists. Water constantly moves from the earth to the air (atmosphere) and back again through different processes such as freezing, melting, evaporation and condensation, this is known as the water cycle, which maintains the water balance in nature.

Domestic Water SupplyExplain to the students that water appears to be clean, but may not be fi t for drinking. It may have impurities and disease causing microorganisms. Thus, it is important to treat it before using it for the purpose of drinking. The Municipal Corporation treats the water before supplying to the households.

Explain to the students about how water reaches our taps at home and undergoes various stages of purifi cation before it reaches us, like sedimentation, decantation, fi ltration, chlorination, storage and supply. Make them aware of the bottled water which is known as mineral water.


Solute, Solvent and SolutionExplain to the students about how a solution is formed (solute + solvent = solution) and different types of solutions like saturated, unsaturated and supersaturated solution.

Component present in larger quantity in a solution is always a solvent.

Substance that is dissolved in a liquid is solute and the liquid is called solvent.

Activity—In a beaker with water, add CuSO4 crystals and stir well.

The colour of water changes and becomes blue. So in this CuSO4 solution, CuSO4 is solute and water is a solvent.

Explain to the students the concept of solubility (ability of a solute to dissolve in a given solvent) and effect of temperature. Solubility increases with temperature. Make them aware about unsaturation and crystallisation.

Activity---Take a saturated salt solution, heat the solution. Salt again dissolves, thus saturated solution becomes unsaturated.

Water PollutionExplain to the students that in this modernised world due to increase in population, number of factories and industries are increasing, as a result there is a lot of waste and pollution generated which is going into water bodies. This results in spoiling the quality of water. The substances that pollute the water are called water pollutants. Make students aware about water pollutants. Factors like faulty drainage system in the country, use of fertilizers by farmers which washes off during rain, waste from nuclear power stations and oil spills from ships, boats leads to water pollution.

Prevention of Water PollutionExplain to the students about different ways of creating awareness amongst people regarding the importance of reducing water pollution. Use of biogas plants and sewage water treatment plants, reduction of use of fertilizers and disposing industry waste into river. The pollution level of river Ganga is

4040

rising day by day as people throw waste, untreated sewage and many other harmful things.

Water ConservartionExplain to the students the importance of ‘Save water, save the earth’. Waste water can be recycled to get pure water. Rainwater harvesting system, which consists of storing water for later use, should be used.

Explain to the students different ways to conserve water like avoid wastage of water and reduce pollution of water, reuse and recycle water and use recycled water for irrigation and watering plants, water

harvesting system and methods to raise water table.




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Worksheet 1

1. Complete the fl ow chart by writing the different uses of water.

a

b

c

de

f

g

Usesof

Water

2. Complete the following change of state of water with temperature.

Water

Condensation

___________

___________

___________ ______________________

___________

(Solid) (Gas)

3. What is rainwater harvesting system? Explain rainwater harvesting system in brief.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

4. Mention any two effects of water pollution.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

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Worksheet 2

1. Name the following.

a. Collection and storage of rainwater for future use ________________

b. Water found in the space between rock particles below ________________earth’s surface

c. Clothes dry in the sunlight by this process ________________

d. Water drops appear on the outer surface of a glass ________________containing cold water

e. Drinking water sold in bottle ________________

f. Ability of a solute to dissolve in a given solvent at a given ________________temperature

g. Set-up that uses human and animal waste, to produce _____________cooking gas

2. List different sources of water.

________________________________________________________________________

________________________________________________________________________

3. Give reasons.

a. A calculated amount of minerals comprising sodium, potassium are added to distilled water before packing.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

b. Dissolution of salt in water is an endothermic change whereas that of sodium carbonate in water is an exothermic change.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

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PART 1

A 1 (b) 2. (b) 3. (b) 4. (b)

5. (b)

B 1. 100 °C 2. hot 3. rain

4. hail storm 5. sea 6. salt

C 1. Nuclear Waste Mix with Water

2. Aquatic life affected

3. Accumulation of garbage

4. Water cycle

5. Poisonous effl uents mix with water

6. Hydroelectricity

D 1. Water Cycle

2. Water pollution

3. Freezing

4. Supersaturated solution

5. Crystallisation

6. Eutrophication

7. Water Balance

PART 2

A 1. The primary source of water is rain.

2. Seawater is salty due to the accumulation of different types of minerals in the oceans or seas. Rivers carry minerals and alluvium which mix with the sea or ocean which they join. Secondly, rain water also brings minerals from the earth’s surface to the seas.

3. Chemically pure water is obtained by distilling ordinary water.

4. The water balance is maintained in nature by the water cycle.

5. Solubility of a solid is the amount of solute which 100 grams of a solvent can dissolve at a given temperature.

6. Evaporation, condensation, sublimation, and precipitation

7. Water keeps the body temperature of humans constant by adjusting excretion in the form of sweat and urine. Water that evaporates from the surface of our body in the form of sweat takes away a lot of heat and thus cools the body.Thus ,the body temperature remains the same .

8. The level maintained by underground water is known as water table.

B 1. Water is called a universal solvent as it can dissolve many compounds in it .

2. All metabolic activities take place in the medium of water. Human body is made up of 70% water. Water regulates our body temperature by adjusting excretion in the form of sweat and urine.

3. On heating a solution, more and more solute can dissolve in the solvent. Therefore, as the temperature rises, a saturated solution becomes unsaturated .

4. Distilled water is -

- used in cooling down engines and cleaning and also to maximise the lifespan of automotive batteries as it doesnot contain minerals that can corrode the metal component of battery.

- Used in laboratory experiments.

5. The fertilizers which the farmers use to increase the crop productivity generally gets washed off with the top soil during rain and are carried to the water bodies. This causes overgrowth of algae and other aquatic plants and causes eutrophication.

6. The nuclear wastes from nuclear power plants dissolved in water produce harmful radiations, which not only kill aquatic life but also causes diseases in human and animals living in coastal areas.

7. The oil spills from ships and boats fl oats on water and deprives aquatic animals of oxygen and also contaminate the sea food we consume.

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C 1. The various sources of water are:

(a) Rain: It is the primary source of water and all the water bodies maintain their water levels because of rain.

(b) Surface water: comprises water bodies present on the earths surface like ocean, sea, river and lake.

River and lakes get water from rain. Ocean and sea are large water bodies where water from rivers join .

(c) Groundwater: Part of the rainwater that percolates down through the rocky layer and collects underground is called ground water.

2. Refer Figure 4.3.

3. Refer Figure 4.4. Sedimentation and decantation – large impurities are removed

↓ Filtration – fi ner impurities are removed

↓ Chlorination – to kill germs

↓ Storage – water stored in big tanks

↓ Supply – clean water is supplied to homes

4. To ability of a solute to dissolve in a given solvent at a given temperature is known as solubility .It is expressed as a percentage.

Solubility = Weight of solute × 100

Weight of solvent For e.g., if 40 gm of a substance can be

dissolved in 100 gm of water at room temperature , the solubility of the substance is 40%.

5. We can show the effect of heat on a saturated solution by the following experiment-

Add a spoonful of salt to water and stir well. When the salt dissolves ,add more salt and stir and continue this process till some salt remains un dissolved .This forms saturated solution.

Now heat the solution and stir well. The salt dissolves and the solution thus

becomes unsaturated. Thus, on heating, as the temperature rises, a saturated solution becomes unsaturated.

Ref .experiment –page 70

6 Solute: A solid that dissolves in a liquid is known as solute.

In a solution of salt and water , salt is the solute.

Solvent: The liquid in which the solid dissolves is called a solvent.

In a solution of salt and water, water is the solvent.

Solution: When a solid dissolves in a liquid, we get a solution.

Solute +solvent =solution

7. Solubility increases with temperature At a given temperature, a saturated solution becomes unsaturated on heating.

Whereas solubility decreases as the solution is cooled. The extra amount of solid comes out of the solution in the form of crystals. This is known as crystallisation.

8. Water is a chemical compound consisting of two hydrogen atoms and one oxygen atom.

- At room temperature, it is a tasteless and odourless liquid.

- It is the only common substance to exist as a solid, liquid and gas on earth’s surface.

- The boiling point of water is 100°C.

- The freezing point of water is 0°C.

- It is a poor conductor of heat and electricity. It conducts electricity only when dissolved impurities are present in it.

- Water is a universal solvent.

9. The presence of unwanted or harmful materials in water is called water pollution. Nature has its own ways of purification. Dust, humus, waste from industries, human and animal excreta are carried into rivers and lakes when rainwater flows

4545

into them. The bacteria present in water purifies the water automatically. But when the quantity of pollutants exceeds the limit, then it is not done naturally. That is what is happening now in the Ganga and Yamuna. The river Ganga, which was once considered a holy river, is now overloaded with pollutants. The same is the case with the river Yamuna and all other major rivers.

D 1. Drinking water which is sold in bottles is labelled as mineral water. Chemically pure water is not fit for drinking so a calculated quantity of minerals comprising sodium, potassium, calcium, iron, etc. is added to it before packing.

2. Clean water that is fit and safe for drinking is called potable water.

3. Water conservation includes all the activities to manage the natural resources of water. For example, rainwater harvesting, minimise the wastage of water by reusing.

4. A part of the rainwater which percolates down through the rocky layer of earth and collects underground is called groundwater. It is drawn up through wells, tubewells and bore wells. Sometimes, groundwater spontaneously comes out as fountains, called springs. Groundwater supplements the demand for water during the summer. But, it is also being overexploited now. People use groundwater for irrigation in places where there are no rivers. As a result, the water table goes down.

E 1. Surface water comprises all the waterbodies, such as oceans, seas, rivers and lakes, which are present on the earth’s surface.

It is exposed to many different contaminants like animal wastes, pesticides,algae etc.

A part of the rainwater percolates down through the rocky layer and collects underground. This is called groundwater.

It contains less contaminants than surface water because rocks tend to act as fi lter to remove some contaminants.

2. A solid that dissolves in a liquid is called a solute. The liquid in which the solid dissolves is called a solvent. The component present in larger quantity in a solution is always a solvent and which is present in smaller quantity is called solute.

For example, in case of salt and water, salt is solute and water is solvent.

The state of solute may change but state of solvent remains the same.

3. A solution in which no more solute can dissolve at a specific temperature is called a saturated solution.

A solution that contains more solute than the solvent can dissolve at a specific temperature is known as a supersaturated solution.

LEARNING ZONE


1. (a) Evaporation

(b) Condensation

(c) Water droplets in the clouds fall down in the form of rain, hail, snow.

(d) Rain water gets collected in the sea, river or oceans or seeps into the ground.

2. If all the rivers dry up, the water balance which is maintained in nature by the water cycle will get disturbed.

3. Fish do not use the oxygen that is bound in water molecules, they use oxygen that is dissolved in the water. If dissolved oxygen is low, as in the case of boiled water, fi sh will die.

4. The density of the egg is higher than the density of tap water, so it sinks. When salt is added to the water, the salt water solution’s density becomes higher than the egg’s, so the egg will fl oat.

Think and answer

1. Salt content in oceans and seas is increasing gradually. Over the ocean, more evaporation as compared to precipitation translates into saltier water. Aside from an increase in evaporation caused by warming, factors such as winds also contribute to changes in salinity.

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2. For an object to fl oat, it must be less dense than the liquid in which it is present. The fact that ice fl oats in water suggests that ice is actually less dense than water.

3. (a) As population increased, and technology developed, nature was overused and misused. Human activities have had adverse effects on natural resources; the air we breathe, the water we drink and the food we eat are all contaminated. Due to increase in the population, the number of industries are increasing and as a result give out poisonous gases and acid vapours which mix with the air and cause acid rains. The increasing number of automobiles due to overpopulation also release smoke having oxides of carbon and sulphur. It also causes large-scale deforestation which increases carbon dioxide in the air.

Due to increase in population, every inch of land available in cities is used for building housing complexes. All these households need water. This increases the demand for potable water. The biological and other wastes generated by this huge population poses the problem of waste disposal. Most

waste ends up in lakes, rivers and garbage heaps. Rainwater carries these garbage heaps into the waterbodies. Thus increase in population is leading to air and water pollution.

(b) Over population leads to the overuse of groundwater and large-scale deforestation leads to less rainfall. The result is an acute shortage of water. The rate at which the demand for water increases and resources decrease will ultimately lead to the unavailability of water, even for basic needs. Due to increase in population most of the land available in cities and suburbs is used for building housing complexes. All these households need water and this increases the demand for potable water.

4. About 71.4% of earth is composed of water still we face a water scarcity because very less percentage of it is fresh water which we can use for day to day purposes .Remaining water is salt water present in oceans and seas. This water cannot be used for drinking, cooking or bathing. Also fresh water available is present in the form of snow.

Answers to WorksheetsWORKSHEET 1 1. a. Drinking, cooking, washing b. Means of transport

c. Producing hydroelectricity d. Irrigation

e. Germination of seeds f. To make soft drinks

g. Used as a solvent in industries

2. Water

Condensation

EvaporationMelting

FreezingLiquid

Steam/Water Vapour___________

___________ ______________________

___________

(Solid) (Gas)

3. The process of collecting and storing rain water for later use is called rain water harvesting. The following two techniques are used:

• Roof top rainwater harvesting – The

rain water which gets collected on the roof-tops is allowed to pass through means of pipe into storage tank at the ground level for later use. This water needs to be fi ltered before use.

4747

• To allow rain water to go into the ground directly from the roadside drains.

4. • Rivers in India are becoming dirty as household and industrial waste is generally thrown into the rivers.

• Top soil which gets washed off with rain, and carried to water bodies is affecting aquatic animals as they do not get enough oxygen to breathe.

WORKSHEET 2

1. a. Rainwater harvesting

b. Underground water

c. Evaporation

d. Condensation

e. Mineral water

f. Solubility

g. Biogas plant

2. a. Chemically pure water if not fi t for drinking. It corrodes the digestive organs, therefore after obtaining the pure water by the distillation of a river water, a calculated amount of minerals are added before packing it into bottles.

b. When salt is dissolved in water, there is drop in temperature. Therefore, it is endothermic change whereas there is an increase in temperature in the case of sodium carbonate, so it is an exothermic reaction.

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Learning Objectives

Students will be able to: know about the atmosphere and its different layers – troposphere, stratosphere,

mesosphere, thermosphere and exosphere

understand the properties of air

understand atmospheric pressure and its application

know the composition of air – air being a mixture of gases

find out the role of oxygen, nitrogen and carbon dioxide

analyse oxygen-carbon dioxide balance in nature

understand air pollution – causes and prevention

know about the greengouse effect and the factors leading to global warming

5 Air and Atmosphere

Warm-upAsk the students some simple questions like– What can they tell about air? Does it smell, have taste, or have weigh? How do people use air everyday? How can they tell that there is air around us even though we can’t see it? Next the teacher and students will perform experiments to prove that air has weight and occupies space; also air (oxygen) is required for burning; Activity – Take a syringe and pull the piston so that air fi lls the syringe tube. Seal the mouth of the syringe. Now try to press the piston. It will be seen that the piston cannot be pressed now because air has fi lled the space of the syringe tube.

Now ask the students to complete the exercise given in the Warm-up section.

Concept ExplanationAir around usExplain to the students that air is one of the

most important resources which is necessary for all living organisms. We are surrounded by air in the form of thin gaseous layer known as atmosphere. It protects the earth like a blanket from the extreme heat and cold and from harmful radiation from outer space.

Activity — to show that air is present everywhere, take a bucket of water and a bottle. When the bottle is dipped upside down straight into the water, no water enters as the bottle is full of air. As soon as the bottle is tilted, air escapes in the form of bubbles. Water enters the bottle to take up the empty space left by the escaping air.

Students should know that atmosphere is extended to several kilometres around the earth and the distribution of air in the atmosphere is not uniform throughout. As we go up, the density of air decreases, the air gets thinner, that’s why mountaineers take their own supply of oxygen.

4949

Explain to the students that according to the density of air, the atmosphere is divided into different layers. (refer to Figure 5.1)

Troposphere – lowermost and most dense layer. It extends up to 10–16 km from sea level.

Stratosphere – extends up to 60 km from sea level. Ozone layer is present which absorbs harmful ultraviolet radiation from the sun.

Mesosphere – It extends up to 85 km from sea level. It is the coldest layer.

Thermosphere – This layer extends from up to 500 km to 1000 km, there is no fixed boundary for this layer. Man-made satellites orbit in this region.

The mesosphere and thermosphere are together called the ionosphere.

Exosphere – It has no boundary, extends to outer space and has almost no air.

Properties of AirExplain to the students that air is colourless and tasteless. It is a mixture of gases and also contains water vapour. Moving air is called wind. Air occupies space and fi lls the space in any empty container. It also exerts pressure which is called atmospheric pressure.

Explain to the students the practical applications of air pressure. A cycle pump, a hand pump for drawing out groundwater, flying kites, using parachute and a syringe are applications of air pressure.

The instrument used to measure atmospheric pressure is called barometer.

Composition of AirExplain to the students that air is a mixture of gases, mainly nitrogen (78% by volume), and oxygen (21%). The remaining 1% is made of gases like argon; carbon dioxide (0.04%). Varying quantities of dust, smoke and water vapour are also present.

Role of different components of air: Explain to the students the role of different components of air.

Nitrogen forms the building block of proteins, enzymes and other cellular constituents that are essential for all forms of life.

Make to students aware about nitrogen cycle. (Refer to Figure 5.3)

Oxygen – oxygen is vital for life and also helps in burning. Materials that burn in air (oxygen) producing large amounts of heat energy are called fuels and this chemical reaction is known as combustion. Fuels can exist in solid state at room temperature (e.g., wood charcoal, cow dung cake, agricultural waste and coal), liquid state (petrol, kerosene oil, diesel and fuel oil), and gaseous state (natural gas, petroleum gas and biogas).

Fuel should be easily available, convenient to transport and store and with high calorifi c value (amount of heat produced by one gram of a fuel). Hydrogen is considered the best fuel, because of its high calorific value. However, it is highly inflammable so used as a rocket fuel. Both methane and LPG have fairly high calorific values and ideal for use as domestic fuels. Compressed natural gas (CNG) is the preferred fuel for automobiles, Both petrol and diesel are mainly used in automobiles but the disadvantage of using these is that their combustion releases harmful gases into the atmosphere.

Explain to the students the difference between process of respiration and photosynthesis. Respiration involves breathing in, getting energy from food and breathing out. It is quite a complicated cycle that eventually produces carbon dioxide and water, when we breathe out. Oxygen is used for artificial respiration for patients. For this, oxygen is stored in cylinders just like cooking gas. Whereas in photosynthesis,

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carbon dioxide is used by green plants to prepare food.

Carbon dioxide + Water →Glucose + Oxygen

Activity – In a test tube, take lime water. When we blow air, the exhaled air enters the lime water. As exhaled air contains carbon dioxide, the lime water turns milky.

Oxygen-carbon dioxide balance in the atmosphere: Explain to the students about the oxygen–carbon dioxide balance in the atmosphere. The percentage of oxygen in the air is maintained by the oxygen given out by plants during photosynthesis. Plants also take up carbon dioxide from the air for photosynthesis, thereby preventing the increase of carbon dioxide in the air. But, because of industries, burning of garbage, decomposition of biodegradable waste and automobiles the balance of these is getting disturbed and more carbon dioxide enters the atmosphere. Thus it is important to maintain a balance of these two gases to save our earth.

Air PollutionExplain to the students that air is one of the most crucial requirements for life. The modernisation is leading to setting up of factories and industries to manufacture goods that we need. As a result, there is lot of waste and pollution generated. As population increased, and technology developed, nature was overused and misused. Human activities have had adverse effects on natural resources; the air we breathe, the water we drink and the food we eat are all contaminated. Air is getting polluted in the following ways:

The increasing number of industries gives out poisonous gases and acid vapours which mix with the air and cause acid rains.

The increasing number of automobiles release smoke having oxides of carbon and sulphur.

Large scale deforestation increases carbon dioxide in the air.

Garbage heaps release foul-smelling gases which cause diseases.

Prevention of Air PollutionExplain to the students various methods for prevention of air pollution like installing convertors in factories to convert harmful gases into harmless ones, minimising the number of automobiles by techniques like car pooling, using public transport, not using motor vehicles for short distances, etc., growing more trees and looking for eco-friendly, non-polluting sources of energy. Government declared the use of CNG and unleaded petrol in Delhi. This has reduced the air pollution remarkably in the city, which was known to be the most polluted city in the world.

Explain to the students that the increased percentage of carbon dioxide will cause the greenhouse effect, i.e. it will not allow the hot rays of the sun to escape from the atmosphere after refl ection once they enter the earth s atmosphere, thereby increasing the temperature of earth. As a result of this, ice on mountains will melt and water level will rise.




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Worksheet 1

1. Fill in the blanks.

a. Moving air is called ______________.

b. ______________ shows the direction in which the air is moving at that place.

c. Aquatic animals use dissolved ______________ in water for respiration.

d. ______________ gas is called greenhouse gas.

e. The gas formed during cellular respiration is ______________.

f. ______________ is the preferred fuel for automobiles these days as it is less polluting.

g. The air that we breathe contains ______________ and the exhaled air contains ______________.

2. What will happen if the percentage of oxygen in the air reaches to 75%?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

3. Why is air considered as a mixture?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

4. What happens when burning continues in a closed room?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

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Worksheet 2

1. Why do mostly traffi c policeman wear a mask?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

2. One is advised to wrap a woollen blanket over a burning object during an incident of fi re. Why?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

3. How can you say that CO2 is produced during respiration?

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

4. Complete the following.

AirOxygen

(a)

Used by plants when nitrogen forms nitrates

(b)

Photosynthesis

(d)

Water Vapour

(c)

Separated

during

Separated

during

Separated during

5. Write two uses of oxygen.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

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PART 1

A 1 (a) 2. (c) 3. (d) 4. (c) 5. (a)

B 1. photosynthesis

2. meteors burn up

3. oxygen

4. domestic fuel

5. more carbon dioxide

6. semiconductor

7. 78% 8. Mesosphere

C 1. True 2. True 3. True

4. False 5. True 6. True

D 1. Oxygen 2. Mesosphere

3. Rhizobium bacteria (nitrogen fi xing bacteria)

4. Carbon dioxide

5. Neon

6. Ozone

7. Barometer

8. Vacuum cleaner, cycle pump, hand pump, water gun

PART 2

A 1. Oxygen is the most important component of air for sustaining life.

2. Carbon dioxide is obtained by burning of fuels. Incomplete combustion results in the formation of carbon monoxide.

3. Nitrogen is important though being inactive because it forms the building block of proteins – important for our skin and hair, and carrying out various processes in our body such as digestion of food, growth and repair.

4. Carbon dioxide, nitrous oxide.

5. When we blow air into lime water, the exhaled air enters the lime water which contains carbon dioxide, thus the lime water turns milky.

6. The ozone layer is important as it absorbs the harmful ultraviolet radiations from the sun.

7. Helium, neon, argon

8. Troposphere, stratosphere, mesosphere, thermosphere and exosphere

9. Lavoisier discovered that air contains nitrogen and oxygen.

B 1. Nitrogen is important for plants for their growth and repair.

2. All the oxygen used for respiration of living beings and combustion is replenished by plants. The percentage of oxygen in the air is maintained by the oxygen given out by plants during photosynthesis. Plants then take up carbon dioxide from the air for photosynthesis, thereby preventing the increase of carbon dioxide in the air, thus maintaining the oxygen –carbon dioxide balance in atmosphere.

3. Nitrogen 78%

Oxygen 20%

Carbon dioxide and other gaese .03%

Inert gases (mainly argon) .97%

Water vapour 1% 4. The pressure exerted by air is called

atmospheric pressure. As we go up, the air pressure decreases because air becomes thinner.

It is measured by an instrument known as barometer which contains mercury in a glass tube. The height of the mercury in the tube indicates atmospheric pressure. It is expressed in centimetres of mercury. For e.g. - Normal pressure is 76 cm of mercury.

5. (a) Minimising the number of automobiles

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by techniques like carpooling, using public transport, not using motor vehicles for short distances, etc.

(b) Growing more trees.

C 1. Refer fi gure 5.1.

2. The majority of organisms cannot utilise nitrogen directly from the atmosphere. Nitrogen is absorbed by plants as nutrients in the form of nitrates. This conversion of atmospheric nitrogen into nitrates is known as the fi xation of nitrogen. A kind of bacteria present in the root nodules of leguminous plants converts atmospheric nitrogen into nitrates. During thunder and lightning, atmospheric nitrogen and oxygen combine to form nitrogen dioxide which dissolves in rainwater and forms nitric acid, which on reaching the soil gets converted to nitrates. On decay, dead plants and animals release nitrogen back into the air. This is called, the nitrogen cycle. (Refer fi gure 5.3)

3. Global warming is the increase in the temperature of the earth’s surface due to an increase in the concentration of gases such as carbon dioxide which traps heat that would otherwise escape from the earth. This is called the greenhouse effect.

It will result in extreme weather conditions such as heat waves, droughts and rain storms; melting of glaciers; rise in sea level and wild life suffering for survival.

4. To show that 1/5th of air contains oxygen we take a burning candle, water in a trough, a gas jar, a strip of paper. Invert the gas jar in the water in the trough such that the water should cover just ¼ of the trough. Note the level of water in the gas jar. Paste a paper strip on the outer side of the jar in such a way that one end of the strip is in line with the water level. Extend the strip up to the base of the jar. Put five marks at equal distance on the strip, to cover the entire strip. Remove the gas jar. Keep the burning candle vertically in the trough. Invert the gas jar over it and we observe that the candle extinguishes after

a few seconds. The water level in the jar rises up to the first mark. This shows that--

Water rises to the first mark of the jar. Therefore, 1/5th of air was used for burning. As oxygen is the only component of air that is used for burning, 1/5th of the volume of air in the jar is oxygen. (Refer Experiment on page 83).

5. The release of harmful substances into the air is called air pollution .Various causes of air pollution are-

(a) The increasing number of industries which give out poisonous gases and acid vapours and mix with the air and cause acid rains.

(b) The increasing number of automobiles release smoke having oxides of carbon and sulphur.

(c) Large scale deforestation increases carbon dioxide in the air.

(d) Garbage heaps release foul-smelling gases which cause diseases.

We can reduce air pollution by following ways—

• Installing convertors in factories to convert harmful gases into harmless ones.

• Minimising the number of automobiles by techniques like car-pooling, using public transport, not using motor vehicles for short distances etc.

• Growing more trees.

• Use of eco-friendly, non-polluting sources of energy.

6. Combustion is a chemical reaction that produces heat and light mostly when oxygen combines with another substance. The most common form of combustion is fi re. For example, when wood burns, the oxygen in the air combines with the carbon in the wood.

Materials that burn in air producing a large amount of heat energy are called fuels.

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Fuels that exist in solid state at room temperature are called solid fuels. Wood charcoal, cow dung cake, agricultural waste and coal are some examples of solid fuels.

Fuels that exist in liquid state at room temperature are called liquid fuels. Petrol, kerosene oil, diesel and fuel oil are some examples of liquid fuels.

Fuels that exist in gaseous state at room temperature are called gaseous fuels. Natural gas, petroleum gas and biogas are some examples of gaseous fuels.

D 1. Combustion is a chemical reaction that produces heat and light. Most forms of combustion happen when oxygen combines with another substance.

2. Eco-friendly products refer to the products that are not harmful to the environment and help to conserve resources like water and energy.

These products also prevent air, land and water pollution. For e.g., eco-friendly clothing and footwear

3. Respiration is the process in which oxygen is taken in to produce energy from glucose and carbon dioxide and water are released when we breathe out.

Food + oxygen → Energy + watervapour + carbon dioxide

4. Fuels that exist in gaseous state at room temperature are called gaseous fuels. Natural gas, petroleum gas and biogas are some examples of gaseous fuels.

5. Deforestation means clearing and cutting of trees and forests and the land is thereafter converted to non-forest use. Deforestation always has a negative impact on the environment i.e. on climatic changes and loss of habitat for a large number of species.

6. Inert gases are the gases that do not take part in chemical reactions i.e. they are chemically non-reactive. Also known as noble gases. For e.g., helium, neon, argon, neon, xenon.

E 1. Fuels that exist in solid state at room temperature are called solid fuels. Wood charcoal, cow dung cake, agricultural waste and coal are some examples of solid fuels.

Fuels that exist in liquid state at room temperature are called liquid fuels. Petrol, kerosene oil, diesel and fuel oil are some examples of liquid fuels.

2. Burning (Combustion) is a chemical and uncontrolled process that takes place at high temperature. It is a fast process in which the energy is released in one step, resulting in increase in temperature and production of fi re whereas respiration is a biological process which is under biological control that take place at normal temperature. It is a slow process and the energy is released in several steps and remain stored in the form of ATP. Only a part of the energy is liberated as heat.

3. Deforestation means cutting of trees in which the upper layer of soil which contain humus gets away from land and converting it as a habitat for human beings It has many ill effects on environment like increase in carbon dioxide level, global warming, climatic changes

Afforestation is planting of trees to increase the area under forests. It helps in maintaining balance in the nature.

4. Respiration is a complex process which includes absorption of oxygen and conversion of complex substances to CO2 and water and release of energy whereas photosynthesis is a process in which plants take in CO2 and water to produce complex carbohydrates with the release of oxygen.

Thus respiration is reverse process of photosynthesis.

LEARNING ZONE


1. (a) and (b) Refer fi g 5.1 Page 82

(c) ozone layer absorbs the harmful ultraviolet radiation from the sun.

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(d) Thermosphere

(e) Troposphere

(f) Stratosphere

2. (a) Greenhouse

(b) Glass has a peculiar property. It doesn’t allow heat radiation to escape from inside and so the interior of the glass house becomes warmer.

(c) Carbon dioxide

(d) The increase in the temperature of the earth’s surface, known as global warming, due to an increase in the concentration of gases such as carbon dioxide which traps heat that would otherwise escape from the earth is called the greenhouse effect.

3. (a) root nodules

(b) A kind of bacteria present in the root nodules of leguminous plants converts atmospheric nitrogen into nitrates.

(c) Leguminous plants

Think and answer

1. Legumes have bacteria in root nodule which takes nitrogen from the air and fi xes it into

the soil in the form of nitrates. This provides this vital element not only for the legume but also other plants in the vicinity. Farmers grow leguminous plants this way to restore the fertility of the soil.

2. As we go up, the atmospheric pressure goes on decreasing and the amount of oxygen also decreases at higher altitude, therefore, mountaineers carry oxygen cylinders with them.

3. Refer Question (E) part 4.

4. In earlier days, man used to utilise what nature provided them but these days due to increased technology, natural resources are being misused. Deforestation occurs to a large extent where large buildings are made instead, even in smaller areas. This results in increase of CO2. As the number of buildings increase, there is increase in the number of automobiles releasing smoke having oxides of sulphur and carbon and gets accumulated in the small region. Also sometimes the multi-storied buildings have improper ventilation or air movement, which can lead to the spread of toxic mold.

Answers to Assessment 2

A. 1. (a) 2. (c) 3. (a) 4. (c)

5. (b)

B. 1. The process of changing water vapour into water on cooling is called condensation.

2. The particles in fluids keep moving rapidly in any direction and bombard each other. This zig-zag movement of tiny microscopic particles suspended in fluids is known as ‘Brownian movement’.

3. The unwanted or harmful materials present in water that makes it unfi t for use are called water pollutants. Dust, humus, human and animal excreta, waste from industries are common examples of water pollutants.

4. The liquid in which the solid (solute) is dissolved is called a solvent. The component present in larger quantity in a solution is always a solvent. In the case of salt solution, salt is the solute and water is the solvent.

5. Waterborne diseases are caused by microorganisms that are transmitted in contaminated fresh water which lead to illness such as cholera and gastrointestinal problems.

C. 1. water vapour-responsible for changes in weather

2. nitrogen-important component of protein

3. helium-used in weather balloons

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4. oxygen-used in respiration

5. carbondioxide-used in photosynthesis

D. 1. solute 2. rain 3. troposphere

4. fuels 5. potable water

E. 1. A solid that dissolves in a liquid is called a solute. The liquid in which the solid dissolves is called a solvent. The component present in larger quantity in a solution is always a solvent.

2. A solution in which no more solute can dissolve at a specific temperature is called a saturated solution and a solution that contains more solute than the solvent can dissolve at a specific temperature is known as a supersaturated solution.

3. When a solid on heating changes into a liquid, it is called melting whereas freezing is defined as the process of changing of liquid state into the solid state on cooling. On freezing, water changes to ice and on melting, ice changes into water.

4. Condensation is defined as the process of changing of a gas into a liquid on cooling. Water vapour condenses to form water whereas the process by which a solid substance changes into a vapour without passing through the liquid state is called sublimation. These solids do not melt.

F. 1. True 2. True 3. False

4. True 5. False

G. 1. Matter can change from one form to the other. The change of matter from one state to another, usually due to a change in temperature, is called the interconversion of the states of matter.

2. The process by which a solid substance changes into a vapour without passing through the liquid state is called sublimation. These solids do not melt.

3. Effect of temperature - solubility increases with temperature. At a given temperature, a saturated solution will become unsaturated on heating. On the other hand, solubility decreases as the solution is cooled.

Stirring - The rate of formation of a solution can be increased by stirring.

Particle size: If the size of the solute is small, the rate of formation of the solution is fast.

4. The random movement of the particles of a matter increases when it is heated. This leads to a change in temperature or a change in the state of the matter. In case of solids, the heat energy supplied is not enough for them to overcome the cohesive force , so solids other than metals do not expand on heating. In liquids, the intermolecular force is not as strong as that in solids and the molecules gain kinetic energy to move farther, thereby increasing the volume. Molecules of gases are not bound by any kind of force, so the heat supplied is solely used to increase the kinetic energy of the molecules and these molecules move away from each other very fast, occupying the entire space available.

5. Diarrhoea, cholera, typhoid fever.

6. a. There should be a proper drainage system for disposal, along with recycling plants for the waste from kitchens and toilets in the villages. They should avoid washing and cleaning clothes and utensils in or near waterbodies.

b. Biogas plants can be set up to use human and animal waste, to produce cooking gas.

c. In cities and towns, sewage water treatment plants should be set up to recycle wastewater.

7. Refer table 5.1 of chapter 5.

H. 1. Process of photosynthesis and respiration are interrelated. The percentage of oxygen in the air is maintained by the oxygen given out by plants during photosynthesis. All the oxygen used for respiration and combustion is replenished by plants. Plants also take up carbon dioxide from the air for photosynthesis, thereby preventing

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the increase of carbon dioxide in the air. Thus, the oxygen-carbon dioxide balance is maintained in nature.

2. To show the presence of air everywhere we take an empty bottle and a tub filled with water. Take the empty bottle and dip it upside down straight into the water. Water does not enter the bottle. Now, tilt the bottle slightly. On tilting the bottle, air bubbles come out and water enters the bottle. Thus, when the bottle is dipped upside down straight into the water, no water enters as the bottle is full of air. As soon as the bottle is tilted, air escapes in the form of bubbles. Water enters the bottle to take up the empty space left by the escaping air.

3. a. When a solute dissolves in a solvent, we get a solution. When a substance dissolves in water, we get an aqueous solution. In the case of common salt and water, salt is the solute and water is the solvent, and the resultant mixture is the salt solution.

b. A solid that dissolves in a liquid is called a solute. When a solute dissolves in a liquid, we get a solution. In the case of salt solution, salt is the solute.

c. Agricultural waste is a waste produced as a result of various agricultural operations. It includes manure and other wastes from farms, poultry houses and harvest waste, fertilizer run –off from fi elds, and pesticides.

4. Water exists in all three states: solid, liquid and gas. Water present in rivers, lakes, seas and oceans is the liquid form of water. Water vapour present in the atmosphere is the gaseous state of water. The three states of water can be converted from one form to another through different processes, such as freezing, melting, evaporation and condensation. When this conversion takes

place in nature, it is called the water cycle. The water balance is maintained in nature by the water cycle.

The sun heats the water in ponds, rivers, lakes and oceans. Water from these sources rises up in the air in the form of water vapour. When water vapour rises up, it cools down and forms water droplets. Many of these tiny droplets combine with dust and other things to form clouds. Inside the clouds, tiny droplets join to form big drops. When clouds become too heavy, they cannot hold the water droplets. So, these water droplets fall down in the form of rain, hail or snow. When water falls as rain or snow, it gets collected in the sea, river, pond, ocean or land. Some water seeps into the ground and recharges the groundwater. When the sun shines and heats up the water, this cycle continues.

5. Harmful substances, such as hydrogen sulphide and carbon monoxide that are released into the air are called air pollutants. As a result of air-pollution, the air we breathe, the water we drink and the food we eat are all contaminated. The increasing number of industries give out poisonous gases and acid vapours which mix with the air and cause acid rains. Large-scale deforestation increases carbon dioxide in the air and garbage heaps release foul-smelling gases which cause diseases.

I. 1. water cycle

2. evaporation, condensation, precipitation, storage. (Refer fi gure 4.3 0f chapter 4.1)

3. Deforestation impacts on the earth’s water cycle. Forests transport large quantities of water into the atmosphere via plant transpiration. This replenishes the clouds and instigates rain that maintains the forests.

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WORKSHEET 1

1. a. Wind

b. Weather Cock

c. Oxygen

d. Carbon dioxide

e. Carbon dioxide

f. CNG

g. 0.3%, 0.4%

2. If any substance catches fi re, it will become diffi cult to extinguish fi re, as oxygen supports combustion.

3. Air contains oxygen and nitrogen as its major constituents besides other gases also which retain their properties in the air. So the air is called a mixture.

4. When burning continues in a closed room, it blows off as burning requires oxygen which gets over eventually.

WORKSHEET 2

1. To prevent inhalation of smoke given out by automobiles.

2. Blanket cuts the supply of oxygen to the object that is burning, thus prevents it from burning.

3. The air we breathe contains 25% oxygen and 0.03% CO2, whereas the exhaled air contains 10% oxygen and 4% CO2. This shows that CO2 is produced during respiration.

4. (a) Respiration/breathing, burning

(b) Carbon dioxide

(c) Condensation

(d) Nitrogen

AirOxygen

Breathing

burning

Used by plants when nitrogen forms nitrates

Carbon-dioxide

Photosynthesis

Nitrogen

Water Vapour

Condensation

Separated

during

Separated

during

Separated during

5. (a) Oxygen is used by human being in the process of breathing.

(b) Oxygen is a combustible gas. It support burning.

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Total marks: 50Time: 3 hours

Model Test Paper 2

Section AA. Fill in the blanks. (5 × 1=5)

1. The air we breathe contains _____________ oxygen and _____________ carbon dioxide.

2. Water exists as _____________, _____________ and _____________.

3. _____________ is used to measure atmospheric pressure.

4. A liquid substance changes into a _____________ on freezing.

5. The ozone gas is present between the _____________ and _____________.

B. Multiple choice questions. (5 × 1=5)

1. CNG is

a. combined natural gas b. compressed nitrogen gas

c. combined neutral gas d. compressed natural gas

2. Which of the following gas is an important component of protein

a. nitrogen b. oxygen c. argon d. carbon dioxide

3. When a substance dissolves in water, we get an

a. aqueous solution b. unsaturated solution

c. acidic solution d. alkaline solution

4. Water cycle maintains the

a. nitrogen balance in nature b. water balance in nature

c. salination d. underground water level

5. Gas used in fi re extinguishers

a. oxygen b. nitrogen c. carbon dioxide d. sulphur

C. State whether true or false. (5 × 1=5)

1. Leguminous plants convert nitrates into nitrogen.

2. As the height from sea level increases, air becomes thinner.

3. Stratosphere is the lowermost layer.

4. Chemically pure water is not fi t for drinking.

5. Water is a poor conductor of heat and electricity.

D. Name the following. (4 × 1=4)

1. The gases that do not take part in a chemical reaction ___________

2. An increase in the temperature of the earth surface due to an increase in the concentration of gases which trap heat ___________

3. An overgrowth of aquatic plants and algae on the surface of water bodies ___________

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4. Water is made fi t for drinking by adding a calculated quantity of mineral salts ___________

Section BA. Defi ne the following. (3 × 1=3)

1. humidity

2. groundwater

3. solvent

B. Short Answer Questions. (4 × 3=12)

1. Differentiate between saturated and unsaturated solution.

2. Explain the effect of temperature on solubility.

3. Why is water cycle important in nature?

4. How would you differentiate between breathing and respiration?

C. Long Answer questions. (4 × 4=16)

1. What is air pollution? List two ways to prevent air pollution. Name two air pollutants.

2. Explain conservation of water. List various ways to conserve water.

3. If 80 grams of a salt can be dissolved in 200 grams of water at room temperature, what is the solubility of the salt at room temperature?

4.

a. Name and defi ne the above process.

b. Indicate the name of the gases on the arrows given.

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Answers to Model Test Paper 1

Section A

A. 1. water generating

2. Au

3. solids, gases

4. molecules

5. residue

B. 1. graphite 2. 2

3. increases 4. reduce fever

5. alloy

C. 1. true 2. true 3. false

4. false 5. true

D. 1. bromine

2. soaps

3. melting point

4. loading

Section B

A. 1. This method of separation is usually preferred when the components are of di�erent sizes and one of the components is small enough to pass through the holes of a sieve. The larger particles remain on the sieve while the smaller particles pass through.

2. The process of treating and handling food to stop or slow down food spoilage and the deterioration of quality, edibility or nutritive value, thus allowing for longer storage, is called food preservation.

3. Matter is anything that occupies space and has mass. Matter can exist in di�erent forms. The space occupied by a material is called volume.

B. 1. Solids have fi xed shape and volume. Molecules are bound by strong intermolecular forces. On the other hand gases have no fi xed shape and volume. The force of attraction between molecules is negligible and gases are free to move in all the space available to them.

2. Physical change

a. Only change of state occurs

b. No new substance is formed.

c. It is reversible.

d. Original substance can be obtained

e. No heat changes occur.

Chemical change

a. A change in chemical composition occurs

b. New substances are formed

c. It is irreversible

d. Original substance cannot be obtained

e. Heat is evolved or absorbed.

3. A mixture is made up of two or more pure substances (elements, compounds or both) that retain their individual properties. The components that make up a mixture are not chemically combined. A mixture does not have specific boiling and melting point or a characteristic colour, smell or taste. In a mixture, the components are present in any proportion. Components can be separated by easy physical means. E.g., air, milk, lemon juice, sweets

4. Molecules of gases are not bound by any kind of force. The heat supplied is solely used to increase the kinetic energy of the molecules and these molecules move away from each other very fast, occupying the entire space available.

C. 1. Non-metals are solids and gases at room temperature. Bromine is the only nonmetal which exists as a liquid at normal temperature. Non-metals are non-malleable and non ductile.

E.g.- Oxygen, sulphur, bromine and iodine are examples of common non-metals.

All non-metals, other than graphite, are bad conductors of heat and electricity. Graphite is the only non-metal which

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conducts electricity. They are not lustrous, except graphite, whereas metals are good conductor of electricity and have lusture.

2. No, the change in POP cannot be reversed since it is a chemical change. It is converted to a new substance. Here the original substance undergoes a change in its composition and, hence, a new substance is formed.


Step 2: Write the valencies of the constituent elements below them


Step 4: If the valency can be simplified, divide both the valencies with the smallest valency of the element

Step 1 Symbol C S

Step 2 Valency 4 2

Step 3 Swap 2 4

Step 4 Formula C S2

4. a. winnowing

b. Winnowing is done during the harvesting of crops. Winnowing is done to separate husk from grains.

c. The mixture is allowed to fall from a height in the form of a spray. The lighter particles fall far away while heavier grains fall near the person winnowing.

Answers to Model Test Paper 2

Section A

A. 1. 21%, 0.03%

2. ice, liquid water, vapour

3. barometer

4. solid

5. troposphere, stratosphere

B. 1. compressed natural gas

2. nitrogen

3. aqueous solution

4. water balance

5. CO2

C. 1. false 2. true 3. false

4. true 5. true

D. 1. inert gases 2. global warming

3. eutrophication 4. mineral water

Section B

A. 1. humidity- The amount of water vapour present in air is called humidity. It varies from place to place, day to day and from time to time.

2. ground water-When it rains, a part of the rainwater percolates down through the rocky layer and collects underground. This is called groundwater. It is drawn up through wells, tubewells and bore wells

3. solvent- The liquid in which the solid dissolves is called a solvent. The component present in larger quantity in a solution is always a solvent.In salt solution, water is the solvent.

B. 1. A solution in which no more solute can dissolve at a specific temperature is called a saturated solution. A solution in which more solute can dissolve at a specific temperature is called an unsaturated solution.

2. Solubility increases with temperature. At a given temperature, a saturated solution will become unsaturated on heating. On the other hand, solubility decreases as the solution is cooled. The extra amount of solid comes out of the solution in the form of crystals. This is called crystallisation.

3. Water exists in all three states: solid, liquid and gas. The three states of water can

6464

be converted from one form to another through di�erent processes. When this conversion takes place in nature, it is called the water cycle. The water balance is maintained in nature by the water cycle.

4. The main purpose of respiration is to produce energy from glucose and oxygen. It is quite a complicated cycle that eventually produces carbon dioxide and water, which are released when we breathe out .Breathing is taking in of oxygen and giving out CO2.

C. 1. The release of harmful substances, such as hydrogen sulphide and carbon monoxide, into the air is called air pollution.

Ways to prevent air pollution-

Minimising the number of automobiles by techniques like car pooling, using public transport, not using motor vehicles for short distances, etc.

Growing more trees.

Common air pollutants are: hydrogen sulphide and carbon monoxide.

2. Overpopulation leads to the overuse of groundwater and large-scale deforestation leads to less rainfall. The result is an acute shortage of water. The rate at which the demand for water increases and resources decrease will ultimately lead to the

unavailability of water, even for basic needs. Therefore, it is essential that we stop the wastage of water and find ways and means to conserve water.

Avoid wasting water. Use water optimally. Reuse and recycle water to the maximum extent possible . Use only recycled water for irrigation or watering plants so that fresh water can be used for household use.

Rainwater should be conserved. 80% of rainwater usually goes waste. Each house or apartment complex should have a provision for water harvesting. Rainwater is made to seep down instead of flowing out. This helps in raising the water table. Plant more trees and prevent deforestation, as rainfall is affected by forest cover.

3. Solubility = Wt. of solute

Wt. of solvent→ × 100

= 80200

× 100 = 40%

4. a. Photosynthesis

It is the manufacture of food by green plants with the help of CO2 and H2O in the presence of sunlight.

b. CO2 is taken inside; O2 is given out.

3. 6CO2 + 6H2O Sunlight

Chlorophyll→

C6H12O6 + 6O2

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6 The Chemistry Science Orbit - SARASWATI HOUSE Material/The Science... · adding chemical preservatives are used to preserve food. Chemistry in Agriculture: Explain to students how