51221647 Form 2 Science Chapter 5

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FORM 2

Science

Chapter 5

Water and solution


Content

5.1 The physical properties of water

5.2 Composition of water

5.3 The process of water evaporation

5.4 Solutions and solubility of substances

5.5 Acid and alkali

5.6 Methods of purifying water

5.7 Water supply system

5.8 Preserving water quality


5.1

The Physical Properties of Water


The Physical Properties of Water

� Water is colourless, tasteless and odourlessliquid

� Water exists in three states, which are solid,liquid and gas

� Water can change from one state to another

� The density of water is 1 g/cm3

� Impurities in water can affect

freezing and boiling point


Change of state of water

Liquid ( Water )

Gas (Vapour )

Freezing

Boiling //

Evaporation Solid ( Ice )

Condensation

Melting




Kinetic theory of freezing point of water

http://fizik-fizik.blogspot.com 9The temperature of steam is taken as the boiling point of water.



Kinetic theory of boiling point of water


5.2

Composition of Water


Composition of Water

Water is a chemical compound that made up of two atoms of hydrogen and one atom of oxygen. (The ratio of

hydrogen to oxygen is 2:1)

Water can be break up into hydrogen and oxygen

through the process of electrolysis.electrolysis.


In the process of electrolysis, oxygen is discharged at the anode (positive electrode) and hydrogen is

discharged at the cathode (negative electrode)

Electrolysis


� Oxygen is tested with a glowing wooden splint. The wooden splint lights up when oxygen is present.

� Hydrogen is tested with a lighted wooden splint. ‘Pop’sound is produced when hydrogen is present

Confirmation test of water composition


5.3

The Process of Water Evaporation


Evaporation of water

• Water evaporation is a process where water molecules are released as vapourinto the air below boiling point of water.


Application of evaporation of water

• The knowledge of evaporation applied in daily life.


Factors that influence the rate of water evaporation

The higher the temperature, the faster the rate of the

water evaporation.

Surrounding temperature

The wider the surface area, the faster the rate of the

water evaporation.

Surface area

Water particles can escape easily when the

atmosphere is dry. Therefore, evaporation process

occurs faster

Air humidity

Moving air (wind) quicken the evaporation process

by blow away the water particles from the water surface

into the atmosphere.

Air movement

(wind)

DescriptionDescriptionFactorsFactors


How to increase evaporation rate in daily life

• Drying hair using hair-

dryer ( the blower

increase air

movement )

• Spread out the

clothes to increase

surface area.

• Wet clothes dry under

hot sun.


Differences between evaporation and boiling

Does not influenced by the

temperature surrounding, air

movement, air humidity and

surface area

Influenced by the temperature

surrounding, air movement, air

humidity and surface area

Occurs throughout the waterOccurs only at water surface

Vigorous processSlower process

Takes place at boiling point

only, that is 100 oC

Takes place at any

temperature below

boiling point

BoilingBoilingEvaporationEvaporation


5.4

Solutions and Solubility of Substances


Solvent, solute and solution

Solvent:Solvent:

A liquid that dissolve a substance (solute)

Solute:Solute:

A substance that soluble or dissolve in a solvent

Solution:Solution:

A mixture of one or more solutes that dissolved in solvent

Dissolves in

to form


Dilute solution, concentrated solution and saturated solution


The solubility of solutes

� The solubility is the number of gram of solute that can dissolve in 100 ml of water at a specific temperature, to form a saturated solution.

� For example, the solubility of potassium nitrate in water is 90 g per 100 ml of water at 50 oC. This means that 90 g of potassium nitrate salt are dissolved in 100 ml of water at a temperature of 50 oC to form a saturated solution of potassium nitrate.


The solubility of solutes


The factors that influence the solubility rate of substances

The higher the temperature, the faster the solute can dissolve in the solvent

Temperature

of solvent

Solutes dissolve more easily in a bigger volume of solvent

Volume of solvent

Solutes dissolve more easily if stirredStirring

The smaller the size of the solute, the faster it can dissolve in the solvent

Size of the solutes

Description Factor


Water as a solvent

Water is known as universal solvent because water can dissolve many types of substances.

The importance of water as a universal solvent.

i. Dissolve oxygen and food so that these can be transfer to body cells.

ii. Most chemical reactions in humans body need water as a solvent.

iii. Dissolve carbon dioxide and oxygen for aquatic organisms.

iv. Dissolves mineral salts and this enables the roots of plants to absorb.


Suspension

• The suspended substances is a substance that

do not dissolve in water.

• When a suspended substances is added into a

solvent, it forms a suspension

• A suspension can be separated by filtration.


Organic solvent

• There are also substances that do not dissolves in water but dissolve in organic solvent such as ether, benzene and alcohol


Organic solvent

to stick plastic

substances

PlasticChloroform

to stick rubber sheetsRubber, greaseBenzene

to dilute paint to make it

easier to use

Grease, paint, tarTurpentine

to make cosmetics such as lipstick and nail polish

Oils, fats, greaseEther

Uses

Substances that can be dissolves

Organic solvent


5.5

Acid and Alkali


Acid and alkaline

Acid and alkali will show their properties in the presence of water

In the presence of water

a) acid will change the colour of

litmus paper from blue to red

b) alkali will change the colour of litmus paper from red to blue


Acid

Acid exists in three states, which are solid, liquid and gas.

Acid are chemical substances that contain hydrogen atom.

Weak acids usually found in food.

Examples are lactic acid, tannic acid, acetic acid, formic acid .


Sources of acids


The properties of acid

1. Taste sour

2. Corrosive

3. Have pH value smaller than 7.

4. Change the colour of litmus paper from blue to red

5. React with carbonates to form salt and water and release carbon dioxide


The properties of acid

6. React with reactive metal (magnesium/aluminium) to form salt and release hydrogen

7. React with alkali to form salt and water (neutralisation process).


• Alkali is a hydroxide or metal oxide that dissolves in water.

• Examples of alkali:

Alkaline


1. Taste bitter

2. Corrosive

3. Have pH value greater than 7

4. Feel slippery like soap when touched

5. Change the colour of litmus paper from red to blue

The properties of alkali


6. React with ammonium salts to give off ammonia gas when heated.

Examples:

sodium hydroxide + ammonium chloride �

sodium chloride + water + ammonia gas

7. React with acids to form salt and water (neutralisationprocess)

The properties of alkali


pH values

Click here to watch video


Neutralisation

• Neutralisation is a chemical reaction in which an acid and an alkali react to form salt and water.

acid + alkali �� salt + water


Titration

• Titration is a method used for neutralisation.

• At the neutralisation point, all the acid completely reacts with the alkali and the solution has a pH value of 7


5.6

Methods of Purifying of Water


Natural source of water

• Natural water contains impurities and needs to be treated before it is safe for drinking.

• Example of natural source of water :

rivers, well, rain , pond, sea, lake, stream..


Methods of water purification

1. Boiling

2. Chlorination

3. Filtration

4. Distillation


Boiling

• Use heat to kills the microorganisms in the water.

• Advantages

Water is free from dangerous microorganisms

• Disadvantages

Dissolved impurities and suspended impurities still exists in water


Chlorination

• Chlorine is added to water to kill microorganisms

• Advantages

Water is free from dangerous microorganism

• Disadvantages

Dissolved impurities and suspended impurities still exists in water


Filtration

• To remove suspended impurities from the water

• Advantages

Water is clear and free from suspended particles

• Disadvantages

Dissolved impurities and

microorganisms still exists in water


Distillation

• To remove suspended impurities and dissolved impurities from the water

• AdvantagesWater is free from all microorganisms, suspended and

dissolved impurities

• Disadvantages

Does not contain minerals which our bodies need.


Distillation


The application of water purification methods in our daily life

(a) Boiling– Piped water is boiled before drinking

(b) Filtration– River water is filtered before being supplied to consumers house

(c) Distillation– Clinics and hospitals use distilled water to prepared medicines

(d) Chlorination– Chlorine is added to the water in the swimming pool to kill microorganisms


5.7 Water Supply System



Water used

• River water and rain water is our main source of water

• The water will then be pump to water purification plants to be purified before it is supplied to consumers home.

• There are several ways to save water

(a) Make use of recycled water

(b) Beware of pipe leakage

(c) Turn off the tap immediately when not in use

(d) Do not turn on the tap full

(e) Wash cloths in big quantities


5.8

Preserving Water Quality


Water pollution

• Water pollution occurs when water is

contaminate with waste product.

• Polluted water is not suitable for living

organisms.


Domestic waste

• Effect of water pollutants

Contains dangerous microorganisms that causes diseases such as cholera.

• Ways to control water pollution

i. Dispose the rubbish in a proper way

ii . Make use of recycle materials instead of using plastic materials


Agricultural waste


Poison the aquatic organisms and affect human’s health

when eaten.


Reduce the used of fertilisers and pesticides


Industrial waste

• Effect of water pollutantsRadioactive wastes and chemical residues will destroy body cells and causes skin cancer


Enforce the law strictly to prevent the factories from letting harmful chemical residues into the open drain


Oil spills


Kills marine life thus affecting the income of fisherman .


Impose heavy penalties and fines to the ships which

found to pollute the sea


Waste water today

- Live in a desert tomorrow.

Documents

51221647 Form 2 Science Chapter 5