Understanding Metals 8. and Non Metalsmt-iconnect.com/MTE_Content/MTE/Notes_Question... · Silver is the best conductor of electricity and next in order is copper. ... They react

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Understanding Metalsand Non Metals8.

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Q.I (A) Fill in the blanks :1. ....................... element that has the highest melting point.2. ....................... is the only non-metal in liquid state.3. Chocolates are wrapped in an aluminium foil, this is an application of

property of ....................... .4. PVC stands for....................... .5. Metal oxides are usually ....................... in nature.6. Aluminium oxide is ....................... in nature.7. Metals react with water to form a metal hydroxide and ....................... gas

is liberated.8. Metals react with dilute acids to give ....................... and .......................

gas is liberated.9. Sodium is a ....................... coloured metal.

10. Chlorine is a ....................... .11. The most unreactive metals i.e. which are not affected by air and water

e.g. silver, gold and platinum are generally found in ....................... state.12. The symbol of Aluminium is ....................... .13. The valency of aluminium is ....................... .14. Aluminum undergoes an oxidation reaction forming a thin layer of

....................... .15. Potassium is the ....................... metal.16. Pure gold is ....................... gold.17. Pure gold is alloyed with ....................... or ....................... to make

ornaments.18. Aqua regia can dissolve metals like....................... and ....................... .

Answers :1. Tungsten 2. Bromine3. malleability 4. poly vinyl chloride5. basic 6. amphoteric7. hydrogen 8. salt and hydrogen gas9. silver 10. non-metal

11. free or native 12. Al13. 3 14. aluminium oxide15. most reactive 16. 24 karat17. silver or copper 18. gold and platinum.

Q.I (B) Match the following :1. Column I Column II(i) Malleability (a) Silver, copper

(ii) Ductility (b) Hammered to sheets(iii) Sonorous (c) Drawn into thin wires(iv) Good conductors (d) Bells in schools, churches

Ans. (i - b), (ii - c), (iii - d), (iv - a).

2. Column I Column II(i) Sodium meta aluminate (a) NaAlO2 or Na2Al2O4

(ii) Sodium oxide (b) Ca(OH)2

(iii) Calcium hydroxide (c) Na2O(iv) Copper sulphate (d) CuSO4

Ans. (i - a), (ii - c), (iii - b), (iv - d).

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3. Column I Column II(i) Potassium (a) greenish yellow poisonous gas

(ii) Sodium (b) Ionic bond(iii) Chlorine (c) Na(iv) NaCl (d) Most reactive element

Ans. (i - d), (ii - c), (iii - a), (iv - b).

4. Column I Column II(i) Metals (a) Negative ions

(ii) Cations (b) Brittle(iii) Non-metals (c) Positive ions(iv) Anions (d) Lustre

Ans. (i - d), (ii - c), (iii - b), (iv - a).

Q.I (C) State whether the following statements are true or false. If falsewrite the corrected statement :

1. Silver is the best conductor of electricity and next in order is copper.Ans. True.

2. PVC is a bad conductor of electricity.Ans. True.

3. Aluminium is a non-metal.Ans. False. Aluminium is a metal.

4. Almost all metals react with oxygen to form metal oxide, but the reactivitydiffers for different metals.

Ans. True.5. Most metal oxides are insoluble in water.

Ans. True.6. Metal oxides dissolve in water to form alkalis.

Ans. True.7. In anodizing technique, a thin film of aluminium oxide is formed on surface

of cathode.Ans. False. In anodizing technique, a thin film of aluminium oxide is formed on

surface of anode.8. Silver and gold react with dilute acids.

Ans. False. Silver and gold do not react with dilute acids.9. Chlorine is a greenish coloured poisonous gas that was used as a weapon

during World War I.Ans. True.10. Most metals however are found in combined state in the form of their

oxide ores, carbonate ores, or sulphide ores.Ans. True.

Q.I (D) Find the odd man out :1. Copper, Silver, Iron, Plastic.

Ans. Plastic as rest all are good conductors.2. Malleability, Ductility, Brittleness, Lustre.

Ans. Brittleness, it is the physical property of a non-metal while rest are physicalproperties of metals.

3. Steel, Iron, Copper, Tungsten.Ans. Steel as it is an alloy, rest are elements.

4. Bauxite, Cinnabar, zinc carbonate, Hydrogen.Ans. Hydrogen as rest are ores of metals.

5. K2O, Na2O, Al2O3, CaO.Ans. Al2O3 as it is an amphoteric oxide while rest are basic oxides.


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6. Galvanizing, Tinning, Anodizing, Roasting.Ans. Roasting as rest are methods to prevent corrosion.

7. Brass, Bronze, Steel, Antimony.Ans. Antimony is a metalloid and rest are alloys.

Q.I (E) Write the correlated terms :1. Metals : ....................... :: Non-metals : Anions.

Ans. Cations.2. Na : Na2O :: Al : ....................... .

Ans. Al2O3.3. Mercury : HgS :: Al :

Ans. Al2O3.H2O.4. K : Na :: Ca : ....................... .

Ans. Mg according to the reactivity series.5. Metals : Reactive :: Noble gases : ....................... .

Ans. Non-reactive.6. Sodium chloride : Ionic bond :: Hydrogen : ....................... .

Ans. Covalent bond.7. Ionic bond : Transfer of electrons from one atom to another :: Covalent

bond : ....................... .Ans. Sharing of electrons.

Q.I (F) Classify the following into metals, non-metals and metalloids :Copper, Iron, Aluminium, Charcoal, Arsenic, Sulphur powder, Pencil(graphite), Antimony.

Ans. Metals : Copper, Iron, Aluminium.Non-metals : Charcoal, Sulphur powder, Graphite.Metalloids : Arsenic, Antimony.

Q.II Define the following :1. Ductility.

Ans. The ability of metals to be drawn into thin wires is called as ductility.2. Malleability.

Ans. The property which allows the metals to be beaten into thin sheets with ahammer without breaking is called as malleability.

3. Sonorous.Ans. The metals that produce a sound on striking a hard surface are said to be

sonorous.4. Metalloids.

Ans. Elements which show properties of both metals and non-metals are calledas metalloids.

5. Anodising.Ans. The process used to make the aluminium surface resistant to corrosion

and abrasion using electrolysis technique is called as anodizing.6. Ionic bond.

Ans. A chemical bond formed by transfer of electron(s) from one atom to anotheratom is called as ionic bond.

MEMORISE :Chemical bond: The force of attraction which is responsible for holdingatoms in a molecule together is called as chemical bond.

– Extra Information.


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7. Ionic compound.Ans. Compounds containing ionic bonds are called as ionic compounds due to

loss or gain of electrons.8. Covalent bond.

Ans. The chemical bond formed by sharing of electrons between two atoms iscalled as covalent bond.

9. Covalent compound.Ans. The chemical compound that is formed by mutual sharing of one or more pairs

of electrons between the two combining atoms is called as covalent compound.*10. Minerals.Ans. The naturally occurring compounds of metals along with other impurities

are known as minerals.*11. Ores.Ans. The minerals from which metals are extracted profitably and conveniently

are called as ores.*12. Gangue.Ans. The impurity of soil, sand and rocky material present in the ore is called

as gangue.*13. Metallurgy.Ans. The process used for extraction of metals in their pure form from their

ores is called metallurgy.14. Reactivity series of metals.

Ans. The arrangement of metals in the decreasing order of their reactivity inthe form of series is called the reactivity series of the metals.

15. Calcination.Ans. The process of converting carbonate ore into oxides by heating strongly in

limited supply of air is called as calcination.*16. Roasting.Ans. The process of converting sulphide ore into oxide by heating strongly in

presence of excess air is called roasting.17. Refining/Electrolytic refining.

Ans. The process of purifying impure metals is called as refining.18. Electroplating .

Ans. It is a process in which an object made up of a conducting material iscoated with a less active metal using electrolysis technique.

19. Corrosion.Ans. Corrosion is degradation of materials due to a reaction with its

environment. ORThe eating up of metals by the action of air, moisture or a chemical (suchas acid) on their surface is called as corrosion.

20. Alloy.Ans. An alloy is an homogenous mixture of two or more metals or a metal and a

non-metal in a definite proportion.21. Galvanising.

Ans. It is a process of giving a thin coating of zinc on iron or steel to protect itfrom corrosion.

22. Tinning.Ans. It is the process of giving a coating of tin, i.e., molten tin over other metal

to prevent it from corrosion.

Q.III Give scientific reasons :*1. Sodium and potassium is stored under kerosene.

Ans. 1. Sodium (Na) and Potassium (K) belongs to group IA, so they are alkalimetals.


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2. They are highly reactive metals.3. Sodium and potassium react with oxygen in air at room temperature to

form metallic oxide. They catch fire and start burning when kept openin the air. Hence, it is stored under kerosene oil to prevent its reactionwith oxygen and moisture.4Na + O2 2Na2O4K + O2 2K2O

MEMORISE :Even lithium is stored under kerosene. – Extra Information.

2. Kitchen articles like pressure cooker, pan etc. are anodized.Ans. 1. Anodising is a technique used to make aluminium surface resistant to

corrosion and abrasion.2. In this process, the anode reaction results in formation of black coloured

thin film of aluminium oxide on the surface of article.4Al + 3O2 2Al2O3

3. Kitchen articles like pressure cooker, pan etc are constantly subjectedto heat, pressure and water causing corrosion and abrasion.

4. To avoid this, kitchen articles are anodized.3. Aluminium oxide is an amphoteric oxide.

Ans. 1. Metal oxides that show both acidic as well as basic properties are knownas amphoteric oxides.

2. They react with acid as well as base to form salt and water.3. Aluminium oxide behaves as an acid while reacting with a base and

behaves as a base while reacting with an acid to form salt and water.Al2O3 + 6HCl 2AlCl3 + 3H2OAluminium oxide Hydrochloric acid Aluminium chloride WaterAl2O3 + 2NaOH 2NaAlO2 + H2OAluminium oxide Sodium hydroxide Sodium aluminate WaterHence, aluminium oxide is an amphoteric oxide.

4. Sodium and chlorine are poisonous substances but sodium chloride is edible.Ans. 1. Sodium chloride is a compound of sodium and chlorine.

2. Physical and chemical properties of constituent elements are notretained in a compound (i.e. properties of sodium and chlorine aredifferent as compared to sodium chloride.)

3. When chemically bonded, these two poisonous substances form acompound sodium chloride so safe that we eat it every day.

5. Some elements occur in free state while others occur in the combinedstate.

Ans. 1. Some elements like noble gases do not have the tendency to combinewith others or even amongst themselves because they have a stableelectronic configuration of duplet or octet. Therefore, they do not havethe tendency to lose or gain or share electrons. Therefore, they occurin free state.

2. While most of the elements like hydrogen, oxygen, sodium, chlorineetc. are active elements. These elements have incompletely filledoutermost orbits and hence show the tendency to lose or gain or shareelectrons in a chemical change. Therefore, they occur in combinedstate.

6. Ionic compounds are formed due to the combination of metals and non-metals.

Ans. 1. A metallic atom loses electrons and gets converted into a positivelycharged ion (cation).


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2. A non-metallic atom gains electrons and gets converted into a negativelycharged ion(anion).

3. These cations and anions have opposite charge and experience a strongattraction for each other, so they remain tightly held together formingionic or electrovalent bond.Hence ionic compounds are formed due to the combination of metalsand non-metals. Eg. : NaCl.Na + Cl Na+ + Cl– NaCl2, 8, 1 2, 8, 7 2, 8 2, 8, 8

7. An aqueous solution of sodium chloride conducts electricity.Ans. 1. A substance shows conduction of electricity due to the movement of

electrons or ions.2. In aqueous solution, sodium chloride splits into sodium ions (Na+) and

chloride (Cl–). These ions are free to move in the solution.Hence, the aqueous solution of sodium chloride conducts electricity.

8. Pure water is a poor conductor of electricity but aqueous solution ofNaCl conducts electricity.

Ans. 1. Pure water does not contain any free ions2. However, when the ionic compound NaCl is dissolved in water, positively

charged Na+ ion and negatively charged Cl– ion get separated fromeach other.

3. Therefore, Na+ and Cl– ions are present in water i.e. aqueous solutionof sodium chloride.These ions are free to move in the solution and hence aqueous solutionof NaCl conducts electricity.

*9. Elements like gold, silver are used to make jewellery.Ans. 1. Gold is a yellow shining metal.

2. Gold metal does not corrode because it is a highly unreactive metalthat remains unaffected by air, water vapour and other gases in theatmosphere.

3. Gold does not tarnish and retains its luster for years.4. Since gold does not corrode, gold ornaments look new after years. So,

it is used to make jewellery because of its bright shiny surface andhigh resistance to corrosion.

10. Elements like gold, silver are found in free or native state.Ans. 1. Metals like gold, silver are placed at the bottom in the reactivity series.

2. They are least reactive metals.3. So, elements like gold, silver are found in free or native state.

11. Electrolysis of active metals like Na, K, Al is not carried out by usingaqueous solution of their chloride.

Ans. 1. Decomposition of an electrolyte by passage of electric current throughit is called as electrolysis.

2. The metals extracted by electrolysis by passing electric current arevery pure, they do not contain impurities.

3. If we carry out electrolysis of aqueous solution of sodium chloride, assoon as sodium metal is produced, it will react with water present inaqueous solution to form sodium hydroxide. Thus we get sodiumhydroxide instead of sodium metal.So, sodium, potassium, calcium metals are obtained by electrolysis ofmolten chloride.

MEMORISE :Molten salt means melted salt, it is produced by strongly heating salt.



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12. Reason for use of fused cryolite (Na3AlF6) along with fluorspar (CaF2)which is added to the electrolytic mixture containing pure alumina.

Ans. 1. Electrolysis requires the electrolyte to be in liquid state.2. Alumina has a very high melting point (> 2000ºC).3. So, electrolysis of alumina is carried out at a much lower temperature

by dissolving it in molten cryolite (Na3AlF6)4. Cryolite has a lower melting point than alumina. The melting point of

solution of alumina in cryolite is lower than cryolite.5. It is further lowered by adding some fluorspar (CaF2).6. Thus, the solution of alumina in cryolite with added fluorspar is

electrolysed at about 1000ºC.13. The graphite (carbon) anodes are periodically replaced during the

electrolysis of fused alumina.Ans. 1. The oxygen evolved at the anode reacts with carbon anode.

2. The carbon anode is thus oxidized to carbon dioxide and escapes outthrough an outlet.C(s) + O2(g) CO2Hence the carbon anode is hence consumed and replaced after a certainperiod of usage.

14. Copper is exposed to air.Ans. 1. When copper is exposed to air for a considerable time, then copper

reacts slowly with the carbon dioxide and water of air to form a greencoating of copper carbonate on the surface of the object.

2. The green copper carbonate is a mixture of copper carbonate and copperhydroxide, CuCO3.Cu(OH)2.

3. Since, copper is low in reactivity series, therefore the corrosion of coppermetal is very slow.

*15. Calcium floats over water during the reaction with water.Ans. 1. Calcium reacts with cold water to form calcium hydroxide and hydrogen

gas.Ca(s) + 2H2O(l) Ca (OH)2(aq) + H2(g)

Calcium Water Calcium hydroxide Hydrogen2. The heat produced is less which is not sufficient to burn the hydrogen

gas. The piece of calcium metal starts floating in water as bubbles ofhydrogen gas formed during the reaction stick to its surface. Thisreaction is less violent.

*16. Ionic compounds have high melting and boiling points.Ans. 1. The ionic compounds are made of positive and negative ions.

2. There is a strong force of attraction between the oppositely chargedions. So a lot of heat energy is required to break this force of attractionand melt or boil the ionic compound. (Sodium chloride has a meltingpoint of 800ºC)So, ionic compounds have high melting point and boiling point.

*17. Tarnished copper utensils are cleaned with lime juice or tamarind.Ans. 1. Copper reacts with moist carbon dioxide in air to form copper carbonate.

As a result, copper vessel loses its shiny brown surface forming a greenlayer of copper carbonate.

2. The copper carbonate is a mixture of copper carbonate and copperhydroxide, CuCO3.Cu(OH)2.

3. The tartaric acid present in the tamarind neutralises the basic coppercarbonate and dissolves the layer.

4. So, tarnished copper vessels are cleaned with lemon or tamarind juiceto give the surface of the copper vessel its characteristic lustre.


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Q.IV (A) Distinguish between :1. Metals and Non-metals.

Ans.

2. Cations and Actions.Ans.

Metals1. State : Metals are generally

solids at room temperature.Exception: Mercury and galliumare liquid at room temperature.

2. Hardness : Metals are generallyhard.Exceptions : Sodium andPotassium can be cut with aknife.

3. Lustre : Metals in their purestate have a brilliant shinecalled as metallic lustre.

4. Density : Metals generally havehigh density.Exceptions : Sodium andPotassium have density lessthan water.

5. Malleability : Metals aregenerally malleable (can bebeaten into sheets).

6. Ductility : Metals are ductile(Drawn or stretched into thinwires). Gold is the most ductilemetal.

7. Metals are good conductors ofheat and electricity. Silver is thebest conductor of electricity andnext in order is copper.

8. Metals are strong and tough,they have high tensile strength.

9. Metals are sonorous, they producea ringing sound when struck.

10. Metals usually have high meltingpoint and boiling point.Exception: sodium andpotassium have low melting point(98ºC and 64ºC).

Non-metals1. State : Non-metals are generally

solids or gases. Exception:Bromine is the only non-metalin liquid state.

2. Hardness : Non-metals aregenerally soft.Exceptions : Carbon in the formof diamond is the hardestnaturally occurring substance.

3. Lustre : Non-metals generally donot have lustre.Exceptions : Iodine crystals anddiamond have lustre.

4. Density : Non-metals generallyhave low density.Exceptions : Diamond is asheavy as aluminium.

5. Malleability : Non-metals are non-malleable, if they are hammeredthey form powdery mass. So, theyare brittle in nature.

6. Ductility : Non-metals are non-ductile.

7. Non-metals are in general badconductors of electricity.Exceptions : Graphite is a goodconductor of electricity.

8. Non-metals are not strong, theyhave low tensile strength.

9. Non - metals are not sonorous.

10. Non- metals have usually lowmelting piont or boiling point.Exception: Diamond has a highmelting point (more than3500ºC).

Cations1. Cations are positively charged

ions.2. Generally, metals produce

cations. Eg. : Na+ (sodium ion),K+ (potassium ion).

3. During electrolysis cations aredischarged at cathode.

Actions1. Anions are negatively charged

ions.2. Generally non-metals produce

anions. Eg. : Cl– (chloride ion), Br–

(bromide ion).3. During electrolysis anions are

discharged at anode.


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3. Atom and Ion.Ans.

4. Chemical properties of metals and Non-metals.Ans.

5. Anode and Cathode.Ans.

Atom

1. An atom is electrically neutral.

2. An atom has all the properties ofthe parent element.

3. An atom may or may not have anindependent existence.

4. In an atom, the outermost orbitmay be unstable. Eg. : Na(Sodium), K (Potassium)

Ion

1. Ion is an atom or group of atomswhich is either positively chargedor negatively charged formed dueto loss or gain of electrons.

2. An ion does not have propertiesof the parent element.

3. An ion does not have anindependent existence.

4. In an ion, the outermost orbit isstable. Eg. : Na+ (sodium ion),K+ (potassium ion)

Chemical properties of metals

1. Metals have 1 to 3 electrons intheir valence shell.Exception : Hydrogen has 1valence electron and helium has2 valence electron.

2. Metals readily lose valenceelectrons to form cations.Na– Na+ + e–

3. Metals generally react with dilacids to form metal salts andliberate hydrogen gas.2Na + 2HCl 2NaCl + H2

4. The oxides of metals aregenerally basic in nature i.e.they react with acids to form saltand water.Exception : Al2O3 is amphotericoxide i.e. react with both acid andbase to form salt and water.Al2O3 + 6HCl 2AlCl3 + 3H2OAl2O3 + 2NaOH 2NaAlO2 + H2O

Chemical properties of non-metals

1. Non-metals have 4 to 7 electronsin their valence shell.Exception : Hydrogen has 1valence electron.

2. Non-metals readily gain or sharethe valence electrons to formanions.Cl + e– Cl–

3. Non-metals generally do not reactwith dilute acids.

4. The oxides of non-metals aregenerally acidic in nature i.e.they react with bases to form saltand water.Exception : Water (H

2O) is

neutral oxide.

Anode

1. It is the electrode connected tothe positive terminal(end) of thebattery.

2. It acquires a positive chargeduring electrolysis and sonegatively charged ions(anions)migrate to the anode.

Cathode

1. It is the electrode connected tothe negative terminal(end) of thebattery.

2. It acquires a negative chargeduring electrolysis and sopositively charged ions(cations)migrate to the cathode.


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6. Calcination and Roasting.Ans.

Q.IV (B) Draw a neat and labelled diagram of the following :1. Action of steam on a metal.

Ans.

Q.V Answer the following in detail :1. Write a short note on anodizing.

Ans. 1. Anodising is one of the applications of electrolysis.2. It is a process of forming a thick oxide layer of aluminium. Aluminium

develops a thin oxide layer when exposed to air. This aluminium oxidecoat makes it resistant to further corrosion and abrasion. The resistancecan be improved by making the oxide layer thicker.

3. In this technique, aluminium article is used as an anode. Electrolyteused is dilute sulphuric acid . The anode reaction results in formationof a black coloured thin film of aluminium oxide on the surface ofanode. By putting appropriate dyes in the electrolytic bath, coloredsurface with decorative finish can be achieved.

4. Kitchen articles like anodised pressure cookers, anodised pans andalso frames of sliding windows are the applications of anodisingtechniques. Anodised name plates are another popular option.

MEMORISE :Decomposition of an electrolyte by passage of electric current through itis called as electrolysis. – Extra Information.

2. What is aqua regia?Ans. 1. Aqua regia is a freshly prepared mixture of 1 part of concentrated nitric

acid and 3 parts of concentrated hydrochloric acid. Thus the ratio ofconc HNO3 and conc HCl in aqua regia is 1:3.

2. It is a highly corrosive and fuming liquid.

Calcination1. In calcinations, ore is heated in

absence of air keeping thetemperature below its meltingpoint so that volatile impuritiesare driven off.

2. It is generally used for carbonateores. Eg. :

ZnCO3 ZnO + CO2

Roasting1. In roasting, the ore is heated at

a temperature below its fusionpoint, but always in the excessof air so that it may be oxidized.

2. It is generally used for sulphideores. Eg. :

2ZnS + 3O2 2ZnO + 2SO2

MetalsampleGlass wool

soaked inwater

Hydrogen

Water

StandBurner


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3. Aqua-regia can dissolve all metals. It can even dissolve gold and platinummetals though concentrated nitric acid or concentrated hydrochloricacid alone cannot dissolve gold or platinum.

3. Explain the formation of sodium chloride.Ans.

1. Sodium atom has one electron in its outermost shell. If it loses oneelectron from its “M” shell then its “L” shell becomes the outermostshell to acquire a stable octet. The nucleus of this atom still has 11protons but the number of electrons has become 10, so there is a netpositive charge giving us a sodium cation (Na+).

2. On the other hand chlorine has 7 electrons in its outermost shell andrequires one more electron to complete its octet. Thus the electronlost by sodium is taken up by chlorine. After gaining one electron, itsK, L and M shells have all together 18 electrons, but the nucleus stillhas 17 protons. This leads to the formation of chloride anion (Cl–) Boththese elements have a give and take relation between them.Sodium and chloride ions, being oppositely charged attract each otherand are held by strong electrostatic forces of attraction to form sodiumchloride (NaCl), resulting in formation of an electrovalent bond or anionic bond. It should be noted that sodium chloride exist as aggregatesof oppositely charged ions in definite geometrical shape.

4. Explain the properties of ionic compounds.Ans. 1. Ionic compounds are solids and hard due to strong force of attraction

between positive and negative ions.2. They are generally brittle and break into pieces when pressure is applied.3. Ionic compounds have high melting and boiling points, as a considerable

amount of energy is required to break the strong intermolecularattraction.

4. They are generally soluble in water and insoluble in solvents such askerosene, petrol etc.

5. Ionic compounds in the solid state do not conduct electricity becausethe movement of ions in the solid state is not possible due to their rigidstructure, but they conduct electricity in the molten state. Theconduction of electricity through a solution involves the movements ofcharged (ions) particles. A solution of an ionic compound in watercontains ions, which move to the opposite electrodes when electricityis passed through the solution.

5. Write a short note on reactivity series of metals.Ans. 1. The arrangement of metals in the decreasing order of their reactivity

in the form of series is called the reactivity series of the metals.

NaSodium atom

ClChlorine atom

Na+

Sodium ion(a cation)

Cl–

Chlorine ion(an anion)

Sodium chloride (NaCl)

p11n12

p17n12

p11n12

p17n18

+ –


SCHOOL SECTION 185

K : Potasssium (most reactive)Na : SodiumCa : CalciumMg : MagnesiumAl : AluminiumZn : Zinc Decreasing order of reactivityFe : IronPb : LeadCu : CopperHg : MercuryAg : SilverAu : Gold (least reactive)

2. Thus the most reactive metal is potassium and is placed in the top ofthe list and least active metal is gold which is placed at the bottom ofthe list.

3. On the basis of reactivity, we can group the metals into following threecategories:(a) Metals of high reactivity.(b) Metals of medium reactivity.(c) Metals of low reactivity.

6. Explain extraction of metals with high reactivity.Ans. 1. The metals high up in the reactivity series are very reactive e.g sodium,

potassium, calcium, aluminum etc. These metals are obtained byelectrolytic reduction. For example Sodium, magnesium and calciumare obtained by electrolysis of their molten chlorides. The metals aredeposited at the cathode (–vely charged electrode), whereas, chlorineis liberated at the anode(+vely charged electrode).The reaction of sodium is as follows :At cathode : Na+ + e- NaAt anode : 2Cl– Cl2 + 2e–

2. Similarly, aluminum is obtained by the electrolytic reduction ofaluminum oxide.At cathode : Al+3 + 3e– AlAt anode : 2O–2 – 4e– O2

3. Thus the highly reactive metals are extracted by the electrolyticreduction of their molten chlorides or oxides.

MEMORISE :Concept of electrolysis: The passage of electricity through an electrolytecauses metallic ions (cations) to migrate towards the cathode and non-metallic ions(anions) to migrate towards the anode.The number of electrons gained by anode is equal to the number ofelectrons donated by cathode.The products of electrolysis are formed at anode and cathode itself sincethe exchange of electrons takes place only at the surface of electrodes.Only hydrogen gas and metals are liberated at cathode.Only non-metals are liberated at anode. – Extra Information.

*7. Describe the Bayer's process for concentration of bauxite.Ans. 1. The most common ore of aluminium is bauxite (Al2O3, H2O).

2. Bauxite contains only 30-70% Al2O3 and the remaining portion is ganguecontaining sand (SiO2), iron oxide (Fe2O3), silica. These impurities areremoved by Bayer's process.

3. In this process, the ore is first crushed and then treated with hotconcentrated caustic soda (NaOH) solution under high pressure for 2


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to 8 hours at 140ºC to 150ºC in a tank called digester. Aluminium oxidebeing amphoteric in nature dissolves in aqueous sodium hydroxide toform water soluble sodium aluminate.Al2O3 + 2NaOH 2NaAlO2 + H2O

4. The iron oxide in the gangue does not dissolve in aqueous sodiumhydroxide and is removed by filtration.

5. However silica from the gangue dissolves in aqueous sodium hydroxideforming water soluble sodium silicate.

6. Diluting sodium aluminate with water and then cooling to 50ºC , it ishydrolysed to give aluminium hydroxide as a precipitate.

NaAlO2 + 2H2O NaOH + Al(OH)37. The precipitate is filtered, washed, dried and ignited at 1000ºC to get

alumina (Al2O3).

2A1(OH)3

º1000 C

Al2O3 + 3H2O

*8. Explain the electrolytic reduction of alumina.Ans. 1. In this process a molten mixture of pure alumina (M.P is > 2000 degree

C ) is electrolysed in a steel tank.2. This tank is lined inside with carbon (graphite) which acts as a cathode,

and a set of carbon (graphite) rods dipped in the molten electrolyte actas anode. Cryolite (Na3AlF6) and fluorspar(CaF2) is also added to themixture to reduce the melting point to about 1000ºC.

3. On passing the current, aluminium is formed at the cathode. The moltenaluminium being heavier than the electrolyte used, sinks to the bottomof the tank from where it is removed periodically. On the other handoxygen is liberated at the anode. The electrode reactions are shownbelow :Anode : 2O–2 – 4e– O2

Cathode : Al+3 + 3e– Al4. The oxygen gas liberated, reacts with carbon anode and forms carbon

dioxide. As the anode gets oxidized during the electrolysis of aluminait has to be replaced from time to time.C + O2 CO2

9. Explain the extraction of moderately reactive metals.Ans. 1. The metals in the middle of activity series such as iron, zinc, lead,

copper etc are moderately reactive. These are usually present assulphides or carbonates in nature.

2. It is easier to obtain a metal from its oxide, as compared to its sulphidesand carbonates.

3. The sulphide ores are first converted into oxides by heating strongly inexcess of air. This process is known as roasting.

Positive carbon anodes

Negativecarboncathode

Steel container

Aluminium

Aluminium outlet

+

–

+ + + +


SCHOOL SECTION 187

4. The carbonate ores are changed into oxides by heating strongly in limitedair. This process is known as calcination.The chemical reaction that takes place during roasting and calcinationof zinc ores is as follows.Roasting : 2ZnS + 3O2 2ZnO + 2SO2 Calcination: ZnCO3 ZnO + CO2 This zinc oxide is then reduced to zinc by using a suitable reducingagent such as carbon.ZnO + C Zn + CO

5. Besides using carbon to reduce metal oxides to metals, highly reactivemetals like sodium, calcium, aluminum etc are also used as reducingagents because they can displace the metal of lower reactivity fromtheir compounds. E.g. when manganese dioxide is heated withaluminum powder, the following reaction takes place.3MnO2 + 4Al 3Mn + 2Al2O3 + HeatThe amount of heat evolved in such reactions is so large that the metalsare produced in the molten state. Another example of this type ofreaction is the thermite reaction in which iron oxide reacts withaluminum to give iron and aluminium oxide evolving a lot of heat.Fe2O3 + 2Al 2Fe + Al2O3 + Heat

10. What is thermite reaction?Ans. 1. The reduction of a metal oxide to form metal by using aluminium powder

as a reducing agent is called as thermit reaction.2. The reaction of metal oxide with aluminium powder is highly exothermic

in which a large amount of heat is evolved.3. The heat liberated is so high that the metals are produced in molten

state.Eg. :Fe2O3(s) + 2Al(s) 2Fe(l) + Al2O3(s) + HeatIron oxide Aluminium Molten iron Aluminium oxide

MEMORISE :The property of reduction by aluminium is made use of in thermite weldingfor joining broken pieces of heavy iron object like girders, railway tracksor cracked machine parts. In the above reaction, molten iron is pouredbetween broken iron pieces to weld them to join them. This process iscalled aluminothermy or thermite welding. Thus thermite welding makesuse of reducing property of aluminium. – Extra Information.

*11. Explain the extraction of less reactive metals. ORExplain the extraction of copper.

Ans. 1. The metals at the bottom of the reactivity series are least reactive.They are often found in free state e.g. gold, silver and copper. Butcopper and silver are also found in combined state as their sulphide oroxide ores.

2. The less reactive metals which are quite low in the reactivity seriesare extracted by the reduction of their oxides by heat alone. Theextraction of copper involves 2 steps :Eg. : Copper which is found as Cu2S in nature can be obtained from itsore by just heating in excess of air (roasting).2Cu2S + 3O2 2Cu2O + 2SO2 When a good amount of copper sulphide has been converted to copperoxide, the supply of air is stopped. In the absence of air, copper oxideformed above reacts with remaining copper sulphide to form coppermetal and sulphur dioxide.


SCHOOL SECTION188

2Cu2O + Cu2S 6Cu + SO2 3. Similarly, cinnabar (HgS) is an ore of mercury. When it is heated in air

in excess of air (roasting), it is first converted into mercuric oxide(HgO).Mercuric oxide is then reduced to mercury on further heating.2HgS + 3O2 2HgO + 2SO2 2HgO 2Hg + O2

*12. What is corrosion and explain the methods to prevent corrosion.Ans. 1. Corrosion of metals can be prevented if the contact between metal and

air is cut off. This is done in a number of ways. Some of the methodsare given below :(a) Corrosion can be prevented if the metal is coated with something

which does not allow moisture and oxygen to react with it.(b) Coating of metals with paint, oil, grease or varnish prevents the

corrosion of metals e.g rusting of iron can be prevented by thismethod.

(c) Coating of corrosive metals with non corrosive metals also preventscorrosion. Some of the methods by which metals can be coatedwith non-corrosive metals are:

2. Galvanizing : It is process of giving a thin coating of zinc on iron orsteel to protect them from corrosion. E.g shiny iron nails, pins extra.

3. Tinning : It is the process of giving a coating of tin, i.e., molten tin overother metal.Eg. : Cooking vessels, made of copper and brass get a greenish coatingdue to corrosion. This greenish coating is poisonous. Therefore theyare given a coating of tin to prevent corrosion. (Kalhai)

4. Electroplating : In this method a metal is covered with another metalusing electrolysis. Silver-plated spoons, gold-plated jewellery, etc, areelectroplated.

5. Anodizing : In this method metals like copper and aluminum areelectrically coated with a thin strong film of their oxides. This filmprotects the metals from corrosion.

6. Alloying : An alloy is an homogenous mixture of two or more metals ora metal and a non-metal in definite proportion. The resultant metalscalled alloys do not corrode easily, e.g. stainless steel.Name of Alloy , constuent elements.(a) Brass (copper and zinc)(b) Bronze (copper and tin)(c) Stainless steel (iron, nickel and chromium)If one of the metal is mercury, then the alloy is known as an amalgam.

*13. Sudha dipped a copper coin in a solution of silver nitrate. After sometime she saw the silver shine on the coin. Why? Give the balancedchemical equation for the same.

Ans. When a copper coin is dipped in silver nitrate solution, the solution becomesblue and shining white deposit of silver metal is deposited on the coppercoin. In this reaction, copper displaces silver forming copper nitrate andsilver metal.Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)

Copper Silver nitrate Copper nitrate Silver*14. Metal A has electronic configuration of 2, 8, 1 and metal B has 2, 8, 8,

2 which is more reactive. Identify these metals and give their reactionswith dil. HCl.

Ans. The elements are sodium and calcium respectively. In the reactivity series,since sodium is placed before calcium, sodium is more reactive than


SCHOOL SECTION 189

calcium. When sodium reacts with dilute hydrochloric acid to give sodiumchloride and hydrogen gas is liberated.2Na(s) + 2HCl(aq) 2NaCl(aq) + H2Sodium Hydrochloric acid Sodium chloride HydrogenWhen calcium reacts with dilute hydrochloric acid to give calcium chlorideand hydrogen gas is liberated.Ca(s) + 2HCl(aq) CaCl2(aq) + H2Calcium Hydrochloric acid Calcium chloride Hydrogen

*15. To obtain Zn from zinc sulphide two chemical reactions are involved

ZnS RoastingA ZnO Reduction

B Zn + CO

Write the equations for A and B.Ans. When zinc sulphide is heated strongly in excess of air, it decomposes to

give zinc oxide and sulphur dioxide gas is liberated.

ZnS(s) + 3O2(g) Roasting2ZnO(s) + 2SO2(g)

Zinc sulphide Zinc oxide Sulphur dioxideWhen zinc oxide is treated with carbon as a reducing agent, zinc oxide isreduced to zinc and carbon is oxidized to carbon monoxide.ZnO(s) + C(s) Zn(s) + CO(g)

Zinc oxide Carbon Zinc Carbon monoxide*16. What is an alloy and give two examples.Ans. An alloy is an homogenous mixture of two or more metals or a metal and a

non-metal in definite proportion. The resultant metals called alloys do notcorrode easily, e.g. stainless steel. Eg. :1. Brass (copper and zinc)2. Bronze (copper and tin)3. Stainless steel (iron, nickel and chromium)If one of the metal is mercury, then the alloy is known as an amalgam.

*17. An element X on reacting with oxygen forms an oxide X2O whichdissolves in water and turns red litmus blue. State the element is ametal or non-metal, explain with proper example.

Ans. 1. As X2O turns red litmus blue, it is a metal oxide. Metal oxides as basicin nature.Metal + Oxygen Metal oxide (basic oxide)So, the element is a metal.

2. Eg. : When sodium reacts with oxygen of air at room temperature toform a metallic oxide called sodium oxide.4Na(s) + O2(s) 2Na2O(s)

Sodium Oxygen Sodium oxide*18. Explain the formation of an ionic compound between metal and a non-

metal by transfer of electrons with Mg as the metal and Cl as a non-metal to illustrate the answer.

Ans.

ClChlorine

atom

Magnesium chloride (MgCl2)

p17n18

p12n12

p17n18

p17n18

p12n12

p17n18

MgMagnesium

atom

ClChlorine

atom

Cl–


Mg2+

Magnesium atom(an anion)

Cl–


– 2+ –


SCHOOL SECTION190

1. Magnesium is a metal whereas chlorine is a non-metal.2. The atomic number of magnesium is 12, so its electronic configuration is

2, 8, 2. It has 2 valence electrons. A magnesium atom donates its valenceelectrons (to two chlorine atoms) and forms a stable magnesium ion (Mg+2).

3. The atomic number of chlorine is 17, so its electronic configuration is2, 8, 7. Chlorine atom has 7 valence electrons. So, it requires only oneelectron to complete its octet. Since one magnesium atom donates twoelectrons, so two chlorine atoms take these two electrons and formtwo chloride ions (2Cl–).

4. The positively charged magnesium ions and negatively charged chlorideions are held together by electrostatic force of attraction to formmagnesium chloride which is an ionic compound.

Q.VI Answer the following questions in one sentence each :1. What are metalloids and give examples?

Ans. Elements which show properties intermediate between metals and non-metalsare called as metalloids. Eg. : Boron, silicon, germanium, arsenic, antimony.

2. Which are the only metals in liquid state?Ans. Mercury and Gallium are the only metals in liquid state.

3. Name the two most ductile metals.Ans. Gold and silver are the two most ductile metals.

4. Name some metals used for cooking purposes.Ans. Copper, Aluminium.

5. Name the metals that can be cut easily with a knife.Ans. Sodium, Potassium are the metals that can be cut easily with a knife.

6. Name the metals that are the best conductors of heat.Ans. Silver and copper are the best conductors of heat.

7. Name the metals that are the poor conductors of heat.Ans. Mercury and Lead are the poor conductors of heat.

8. Name the element that has the highest melting point.Ans. Tungsten.

9. Name the substance that is the hardest substance.Ans. Carbon in the form of diamond is the hardest substance.10. Name the elements that have low melting point.

Ans. Sodium and Potassium are the elements that have low melting point.11. Name the non-metals that are lustrous.

Ans. Iodine and diamond(allotrope of carbon) are the non-metals that are lustrous.12. Name the non-metal that is a good conductor of electricity.

Ans. Graphite (allotrope of carbon) is a non-metal that is a good conductor ofelectricity.

13. Which property of graphite is utilized in making electrodes?Ans. Carbon (in the form of graphite) conducts electricity. This property of graphite

is utilized in making electrodes.

MEMORISE :The melting point of gallium and caesium metals are 30ºC and 28ºC, theystart melting in hand. – Extra Information.

14. Name the metals that do not react with water.Ans. Gold, silver and copper do not react with water at all.15. Name a few noble gases.

Ans. Helium, Argon, Neon, Krypton, Xenon, Radon are examples of noble gases.16. What is ionic bond also called as ?

Ans. Ionic bond is also called as electrovalent bond.


SCHOOL SECTION 191

17. Name a few ionic compounds.Ans. Sodium chloride, potassium chloride, calcium chloride, magnesium chloride

are examples of a few ionic compounds.18. What does extraction of aluminium involve:

Ans. The extraction of aluminium involves :1. Concentration of ore and i.e. conversion of bauxite to alumina by Bayer's

process.2. Electrolytic reduction of pure alumina.

19. Name two reducing agents.Ans. Carbon and aluminium powder are the reducing agents.20. Name the widely used method for refining impure metals (like copper,

zinc, tin, lead, chromium, nickel, silver, gold).Ans. The widely used method for refining impure metals is electrolytic refining.

MEMORISE :Electrolytic refining:It means refining by electrolysis. It is done as follows:A thick block of impure metal is made anode.A thin strip of pure metal is made cathode.A water soluble salt(of the metal to be refined) is taken as electrolyte.On passing electric current, impure metal dissolves from anode and goesinto the electrolyte solution. And pure metal from the electrolyte depositson cathode. The soluble impurities present in impure metal go into thesolution whereas insoluble impurities settle down at the bottom of anodeas anode mud. – Extra Information.

21. Name the metal that is highly resistant to corrosion.Ans. Aluminium is a metal that is highly resistant to corrosion*22. Name a metal that forms amphoteric oxide.Ans. Aluminium is a metal that forms amphoteric oxide.*23. Name an alloy of copper and zincAns. Brass is an alloy of copper and zinc.*24. A compound which is added to lower the fusion temperature of an

electrolytic bath in extraction of aluminium.Ans. Cryolite (Na3AlF6) and fluorspar (CaF2) are the substances added to lower

the fusion temperature of an electrolytic bath in extraction of aluminium.*25. A metal which does not react with cold water but reacts with steam.Ans. Magnesium is a metal which does not react with cold water but reacts

with steam.*26. A common ore of aluminium.Ans. Bauxite (Al2O3.H2O) is the common ore of aluminium.*27. Name one metal occurring as sulphide.Ans. Zinc sulphide, Cinnabar or mercuric sulphide (HgS) is a sulphide ore.*28. Name one metal occurring as carbonate.Ans. Zinc carbonate (ZnCO3) is a carbonate ore.*29. Name one metal occurring as oxide.Ans. Bauxite (Al2O3.H2O) is an oxide ore.30. Arrange the following metals in the decreasing order of chemical

reactivity.Cu, Mg, Fe, Na, Ca, Zn.

Ans. The order of metals according to decreasing reactivites are :Na, Ca, Mg, Zn, Fe, Cu.


SCHOOL SECTION192

Q.VII Explain the following chemical reactions with the help of balancedequations :

1. Sodium reacts with oxygen.Ans. When sodium reacts with oxygen of air at room temperature to form a

metallic oxide called sodium oxide.4Na(s) + O2(g) 2Na2O(s)

Sodium Oxygen Sodium oxide2. Potassium reacts with oxygen.

Ans. When potassium reacts with oxygen of air at room temperature to form ametallic oxide called potassium oxide.4K(s) + O2(g) 2K2O(s)

Potassium Oxygen Potassium oxide3. Sodium oxide reacts with water.

Ans. When sodium oxide reacts with water it forms an alkali, sodium hydroxide.Na2O(s) + H2O(l) 2NaOH(aq)

Sodium oxide Water Sodium hydoxide4. Potassium oxide reacts with water.

Ans. When potassium oxide reacts with water, forms an alkali, potassiumhydroxide.K2O(s) + H2O(l) 2KOH(aq)

Sodium oxide Water Sodium hydoxide5. Magnesium metal is heated.

Ans. When magnesium is heated, magnesium metal burns in air giving intenseheat and light to form a white powder of magnesium oxide.2Mg(s) + O2(g) Heat 2MgO(s)

Magnesium Oxygen Magnesium oxideMagnesium metal does not react with oxygen at room temperature, it hasto be heated.

6. Zinc metal is strongly heated.Ans. When zinc metal is strongly heated, zinc metal burns in air giving zinc

oxide.2Zn(s) + O2(g) Heat 2ZnO(s)

Zinc Oxygen Zinc oxide7. Iron filings are sprinkled in the flame of the burner.

Ans. When iron filings are sprinkled in the flame of burner, it burns vigorouslyto form iron oxide.3Fe(s) + 2O2(g) Heat Fe3O4(s)

Iron Oxygen Iron oxideIron metal does burn in air even on strong heating.

8. Copper metal is continuously heated.Ans. Copper metal does not burn in air even on strong heating. Copper reacts

with oxygen of air on prolonged heating to form a black substance copperoxide.2Cu(s) + O2(g) Heat 2CuO(s)

Copper Oxygen Copper oxide9. Aluminium metal is exposed to air.

Ans. When alumiunium metal is exposed to air or on heating forms a thin layerof aluminium oxide.4Al(s) + 3O2(g) Heat 2Al2O3(s)

Aluminium Oxygen Aluminium oxide10. Sodium reacts with cold water.

Ans. 1. When sodium reacts with cold water, sodium hydroxide is formed andhydrogen gas is liberated.


SCHOOL SECTION 193

2. The reaction is very vigorous and produces a lot of heat. So, it is anexothermic reaction.

3. The heat released is so high that the hydrogen gas formed catches fireand causes little explosion.2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

Sodium Water Sodium hydroxide Hydrogen11. Potassium reacts with cold water.

Ans. 1. When potassium reacts with cold water, potassium hydroxide is formedand hydrogen gas is liberated.

2. The reaction is very vigorous and produces a lot of heat. So, it is anexothermic reaction.

3. The heat released is so high that the hydrogen gas formed catches fireand causes little explosion.2K(s) + 2H2O(l) 2KOH(aq) + H2(g)

Sodium Water Sodium hydroxide Hydrogen12. Calcium reacts with cold water.

Ans. 1. Calcium reacts with cold water to form calcium hydroxide and hydrogengas.Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g)

Calcium Water Calcium hydroxide Hydrogen2. The heat produced is less which is not sufficient to burn the hydrogen

gas. The piece of calcium metal starts floating in water as bubbles ofhydrogen gas formed during the reaction stick to its surface. Thisreaction is less violent.

*13. Aluminium reacts with steam.Ans. When aluminium reacts with steam to form aluminium oxide and hydrogen

gas. Aluminium does not react with water under ordinary conditions becauseof a thin and tough layer of aluminium oxide on its surface.2Al(s) + 3H2O(g) Al2O3(s) + 3H2(g)

Aluminium Water Aluminium oxide Hydrogen14. Zinc reacts with steam.

Ans. When zinc reacts with steam to form zinc oxide and hydrogen gas.Zn(s) + H2O(g) ZnO(s) + H2(g)

Zinc Water Zinc oxide Hydrogen15. Iron reacts with steam.

Ans. When iron reacts with steam to form iron (II, III)oxide and hydrogen gas.3Fe(s) + 4H2O(g) Fe3O4 + 4H2(g)

Iron Water Iron oxide Hydrogen*16. Magnesium reacts with hot water.Ans. When magnesium reacts with hot water to form magnesium oxide and

hydrogen gas is liberated.Mg(s) + 2H2O(l) Mg(OH)2(aq) + H2(g)

Magnesium Water Magnesium hydroxide Hydrogen17. Magnesium reacts with dilute hydrochloric acid.

Ans. When magnesium reacts with dilute hydrochloric acid, it gives magnesiumchloride and hydrogen gas is evolved.Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

Magnesium Hydrochloric acid Magnesium chloride Hydrogen18. Aluminium reacts with dilute hydrochloric acid.

Ans. When aluminium reacts with dilute hydrochloric acid to give aluminiumchloride and hydrogen gas.2Al(s) + 6HCl(aq) 2AlCl3(aq) + 3H2(g)

Aluminium Hydrochloric acid Aluminium chloride Hydrogen


SCHOOL SECTION194

19. Zinc reacts with dilute hydrochloric acid.Ans. When zinc reacts with dilute hydrochloric acid to give zinc chloride and

hydrogen gas.Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

Zinc Hydrochloric acid Zinc chloride Hydrogen20. Iron reacts with dilute hydrochloric acid.

Ans. When iron reacts with cold dilute hydrochloric acid to give iron(II) chlorideand hydrogen gas.Fe(s) + 2HCl(aq) FeCl2(aq) + H2(g)

Iron Hydrochloric acid Iron chloride Hydrogen21. Lead reacts with dilute hydrochloric acid.

Ans. When lead reacts with dilute hydrochloric acid to give lead chloride andhydrogen gas.Pb(s) + 2HCl(aq) PbCl2(aq) + H2(g)

Lead Hydrochloric acid Lead chloride Hydrogen22. Iron reacts with dilute sulphuric acid.

Ans. When iron reacts with dilute sulphuric acid to give iron sulphate andhydrogen gas.Fe(s) + H2SO4(aq) FeSO4(aq) + H2(g)

Iron Sulphuric acid Iron sulphate Hydrogen23. Zinc reacts with dilute sulphuric acid.

Ans. When zinc reacts with dilute sulphuric acid to give zinc sulphate andhydrogen gas.Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)

Zinc Sulphuric acid Zinc sulphate Hydrogen24. Magnesium reacts with dilute sulphuric acid.

Ans. When magnesium reacts with dilute sulphuric acid to give magnesiumsulphate and hydrogen gas.Mg(s) + H2SO4(aq) MgSO4(aq) + H2(g)

Magnesium Sulphuric acid Magnesium sulphate Hydrogen25. Magnesium reacts with dilute nitric acid.

Ans. When magnesium reacts with dilute nitric acid to give magnesium nitrateand hydrogen gas is evolved.Mg(s) + 2HNO3(aq) Mg(NO3)2(aq) + H2(g)

Magnesium Nitric acid Magnesium nitrate Hydrogen26. Manganese reacts with dilute nitric acid.

Ans. When manganese reacts with dilute nitric acid to give manganese nitrateand hydrogen gas is evolved.Mn(s) + 2HNO3(aq) Mn(NO3)2 + H2(g)

Manganese Nitric acid Manganese nitrate Hydrogen

MEMORISE :When a metal reacts with dilute nitric acid, hydrogen gas is not evolved.Nitric acid is a strong oxidizing agent. As soon as hydrogen gas is formedbetween a metal and dilute nitric acid, nitric acid oxidizes hydrogen towater. Nitric acid oxidizes hydrogen to water and nitric acid itself getsreduced to any one of the nitrogen oxides like dinitrogen monoxide (N2O),nitrogen monoxide (NO) or nitrogen dioxide (NO2) . The type of oxide dependson the nature of metal, the temperature of reaction and concentration ofnitric acid. Very dilute nitric acid however reacts with magnesium andmanganese to liberate hydrogen gas. Thus is because dilute nitric acid isa very weak oxidizing agent and is not able to oxidize hydrogen to water.



SCHOOL SECTION 195

27. Iron nail is placed in copper sulphate solution.Ans. When iron nail is placed in copper sulphate solution, more reactive iron

displaces less reactive copper and the blue colour of copper sulphate fadesgradually to give a greenish solution of iron sulphate and reddish browndeposit of copper is obtained. This is a displacement reaction.Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

Iron Copper sulphate Iron sulphate Copper

MEMORISE :Cu does not react with FeSO4 as Cu is less reactive than iron.


28. Aluminium hydroxide is heated.Ans. When aluminium hydroxide is heated at around 1000ºC, it forms pure

aluminium oxide called alumina.2Al(OH)3(s) Al2O3(s) + 3H2O(g)

Aluminium hydroxide Alumina Water29. Sodium aluminate is hydrolysed.

Ans. When sodium aluminate is hydrolysed, it gives sodium hydroxide andprecipitate of aluminium hydroxide.NaAlO2(aq) + 2H2O(l) NaOH(aq) + Al(OH)3 Sodium aluminate Water Sodium hydroxide Aluminium hydroxide

30. Zinc carbonate is heated in limited supply of air.Ans. When zinc carbonate is heated in limited supply of air, it decomposes to

give zinc oxide and carbon dioxide gas is liberated.

ZnCO3(s) Calcination ZnO(s) + CO2(g)

Zinc carbonate Zinc oxide Carbon dioxide31. Aluminium oxide dissolves in aqueous sodium hydroxide.

Ans. When aluminium hydroxide(being amphoteric in nature) dissolves inaqueous sodium hydroxide, it gives water soluble sodium aluminate,Al2O3 + 2NaOH 2NaAlO2 + H2OAluminium oxide Sodium hydroxide Sodium aluminate Water

32. Zinc sulphide is heated in excess of air.Ans. When zinc sulphide is heated in excess of air, it decomposes to give zinc

oxide and sulphur dioxide gas is liberated.

2ZnS(s) + 3O2(g) Roasting2ZnO(s) + 2SO2(g)

Zinc sulphide Oxygen Zinc oxide Suphur dioxide33. Zinc oxide is treated with carbon.

Ans. When zinc oxide is treated with carbon as a reducing agent, zinc oxide isreduced to zinc and carbon is oxidized to carbon monoxide.ZnO(s) + C(s) Zn(s) + CO(g)

Zinc oxide Carbon Zinc Carbon monoxide34. Manganese dioxide is heated with aluminium powder.

Ans. When manganese dioxide is heated with aluminium powder, Al displacesMn. The reduction of manganese dioxide takes place by aluminium andaluminium gets oxidized to aluminium oxide. Since this reaction is a highlyexothermic reaction, manganese is obtained in molten form.3MnO2(s) + 4Al(s) 3Mn(l) + 2Al2O3(s) + HeatManganese Aluminium Manganese Aluminiumdioxide powder metal oxide

*35. Iron oxide reacts with aluminium.Ans. When iron oxide and aluminium powder is heated, aluminium reduces

iron oxide to produce iron metal and aluminium gets oxidized to form


SCHOOL SECTION196

aluminium oxide. Since this reaction is a highly exothermic reaction, ironmetal is obtained in molten form.Fe2O3(s) + 2Al(s) 2Fe(l) + Al2O3(s) + HeatIron oxide Aluminium molten Iron Aluminium oxide

36. When cinnabar is heated in excess of air (roasting).Ans. When cinnabar is heated is roasted in air, it gives mercuric oxide and

sulphur dioxide gas is liberated.2HgS(s) + 3O2(g) 2HgO(s) + 2SO2(g)

Mercuric sulphide Oxygen Mercuric oxide Sulphur dioxide37. Mercuric oxide is heated.

Ans. When mercuric oxide is heated, it decomposes to form mercury metal.

2HgO(s) 2Hg(s) + O2

Mercuric oxide Mercury Oxygen

MEMORISE :Metal + Oxygen Metal oxideMetal + Water Metal hydroxide+ HydrogenMetal + Steam Metal oxide + HydrogenMetal + Dilute HCl Metal salt (metal chloride) + HydrogenAbove metal is above hydrogen in reactivity series.Reactivity decreases in the order, Mg > Al > Zn > Fe and copper does notreact with HCl at all.Metal + Dil. H2SO4 Metal sulphates and hydrogen gasMetal + Dilute HNO3 Metal nitrate + Hydrogen gasSalt solution of metal B + Metal A Salt solution of metal A + Metal B.



SCHOOL SECTION 197

ACTIVITY BASED QUESTIONS

ACTIVITY : 8.1

• Take sample pieces of copper, iron, aluminium, charcoal, sulphur powder,pencil lead (graphite).

• Identify and classify the above samples as metals and non-metals.Q. Which features did you consider to classify them ?

Ans. Metals : Copper, iron, aluminium, lead.Non metals : Sulphur.The chemical and physical properties of metals and non metals wereconsidered such as physical state, melting point, boiling point density, ,malleability, ductility, hardness conduction of heat.

ACTIVITY : 8.2

• Take samples of metals like iron, copper, aluminium and magnesium.• Note the appearance of each sample.• Clean the surface of each sample with sand paper and note their

appearance again.Ans. Iron, copper, aluminium and magnesium are all metals. Metals in their

pure state have a shine and after they are polished they show highlyreflective surface.

ACTIVITY : 8.3

• Take a lid of a cold drink bottle, a coin, a thick aluminium wire.• Strike it with a hammer several times.

Q. What do you observe ? Record the change in the shapes of these metals.Ans. The lid of cold drink bottle, coin and aluminium wire all are made up of

metals.Metals have the ability to withstand hammering and can be made into thinsheets which is called as malleability.

ACTIVITY : 8.4

Q. Observe the zari borders of pure silk sarees eg. paithani - what is thiszari made up of ? Why do you think intricate designs with zari can bewoven in a saree ?

Ans. The zari borders of pure silk sarees eg. paithani are made up of gold,silver, copper. The intricate designs with zari can be woven in a sareebecause gold, silver, copper are metals. Metals have the ability to be drawninto thin wires i.e. ductility and gold and silver are most ductile metals.

Q. Remove the insulation of an electric wire what do you observe ?Ans. If we remove the insulation of an electric wire we can observe thin wires

made up of the metal copper.Q. Observe the gold and silver jewellery.

Ans. Gold and silver jewellery as intricate designs which is possible only becausegold and silver are the most ductile metals.


SCHOOL SECTION198

ACTIVITY : 8.5

• Take an aluminium or a copper wire, clampthis wire on a stand as shown in figure8.1.

• Keep a wedge of butter on free end of wire.• Heat the wire with a spirit lamp or a

burner near the place where it is clamped.Q. Does the butter melt ?Q. Note your observations.

Ans. When an aluminium or copper wire clamped on a stand and a wedge ofbutter is kept on free end of the wire. When we heat the wire the butterstarts melting because metals like copper and aluminium are goodconductors of heat.

ACTIVITY : 8.6

• Set up an electrical circuit as shown in figure 8.2.• Place the metal to be tested in the circuit between the terminals, A and B.

Q. Does the bulb glow ? What does this indicate ?Ans. The electric circuit is set as shown in the diagram and metal is placed

between terminal A and B. The bulb glows indicating metals are goodconductors of electricity.

Q. What is the inside and outside material of an electric wire ?Ans. The electric wires are made up of (inside material) copper and outer coating

or outside material of an electric wire is of polyvinyl chloride (PVC).

ACTIVITY : 8.7

• Take samples of iron nail, thick copper and aluminium wire and magnesiumribbon.

• Take a piece of sodium metal in a watch glass. (handle sodium metalcarefully strictly under supervision)

Q. Try to cut these samples with a sharp knife and note your observations.Ans. Metals are generally hard and the hardness differs from metals to metals.

The iron nail, thick copper are hard metal and cannot be cut with help ofknife but aluminium wire, magnesium wire, sodium metal are soft metalwhich can be cut with a sharp knife.

ACTIVITY : 8.8

• Take the samples of coal, graphite, sulphur, iodine and bromine.Q. Carry out the above activities with these non metals and record your

observations.Ans. Coal, graphite, sulphur, iodine and bromine are all non metals.

All these elements do not have lusture except iodine.They are not hard, malleable or ductile.They cannot conduct electricity except graphite.

ACTIVITY : 8.9

The following activity to be done under teacher’s supervision :• Hold any of the samples taken above with a pair of tongs over a flame.

Repeat with the other metal samples except sodium.

Stand Butter

Burner

Metal wire


SCHOOL SECTION 199

• Collect the product formed.• Let the product and the metal surface cool down.• Which metals burn easily ?

Ans. Aluminium, magnesium, zinc and iron burns easily.• How does the metal surface appear after burning ?

Ans. After burning they get coated with different coloured layers.Eg. copper after burning gets coated with black coloured layer.

• Are the products soluble in water ?Ans. The products are insoluble in water.

ACTIVITY : 8.10

• Take the samples of the same metals as in activity 8.9 to perform theactivities given below.

• Put some pieces of samples separately in beakers half filled with coldwater.

Q. Which metals reacted with cold water ?Ans. Metals like sodiium reacted with cold water.

Q. Did any metal catch fire in water ?Ans. Yes, sodium catches fire immediately because sodium reacts with water

and hydrogen gas is evolved which produces lot of heat.Q. Does any metal start floating after some time ?

Ans. Magnesium starts floating after some time because of hydrogen gas stickto its surface.

ACTIVITY : 8.11

• Take the metal samples of iron, zinc, aluminium, copper, lead, etc., inseparate test tubes.

• Add dilute hydrochloric acid in each of them.• Observe the formation of bubbles carefully.

Q. Which metals reacted vigorously with dilute hydrochloric acid ?Ans. Magnesium, aluminium, zinc and iron react vigorously with dilute

hydrochloric acid to form metal chloride and hydrogen gas.Lead and copper do not react with dilute hydrochloric acid.

ACTIVITY : 8.12

• Take a clean copper wire and an iron nail.• Put the copper wire in a solution of magnesium chloride and an iron nail

in the solution of copper sulphate.Q. Record your observation after sometime.

Ans. The iron nail immersed in copper sulphate solution gets coated with reddishbrown colour copper and blue colour of copper sulphate fades out becausein this more reactive iron displaces copper which is less reactive from thecopper sulphate solution. There is no change when copper wire is immersedin magnesium chloride because copper is less reactive and magnesium ismore reactive and therefore less reactive metal cannot displace morereactive element. Sodium chloride, potassium iodide, barium chloride aresolid.Sample is soluble in water but insoluble in kerosene and petroleum.In all the above examples when current is passed bulb glows, proving theyare electrolytes.


SCHOOL SECTION200

HOTS QUESTIONS & ANSWERS

1. A metal X does not burn even on strong heating but its fillings burnvigorously when sprinkled in the flame of the burner. Name the metaland the compound formed in the process.

Ans. Metal X is iron and the compound formed is ferrous oxide.

2. My friend says that diamond is a substance which has luster and is veryhard to break. Therefore it belongs to the family of metal. Do you agreewith the view ? Why ?

Ans. Diamond is a form of carbon which is a non-metal. Although characteristicslike having luster and being hard to break resemble to those in the familyof metals other aspects such as malleability, ductility etc. are not presentin diamond thus making it a non-metal.

3. Why does sodium combine with chlorine and not with sulphur ?Ans. Atomic number of sodium is 11. Chlorine is 17 and sulphur is 16. The

electronic configuration of sodium is (2, 8, 6). The electron lost by sodiumis taken up by chlorine to make sodium chlorine whereas sulphur needs 2electrons which sodium does not have. Thus sodium does not combinewith sulphur.

4. Create chemical equations for the following statement :(a) Iron reacts with hydrochloric acid to give iron chloride and hydrogen

gas.Ans. Fe + 2HCl FeCl

2 + H

2

(b) Aluminium powder was brought in the contact of steam it formedaluminium oxide and hydrogen gas.

Ans. 2Al + 3H2O Al

2O

3 + 3H

2

(c) Zinc is separated from zinc oxide in presence of carbon and carbonmonoxide is produced in the process.

Ans. ZnO + C Zn + CO

5. What interpretation could be made from the reaction given below ?2HgO heat 2Hg + O2

Ans. Mercuric oxid is reduced to mercury on heating. This process is called asreduction in which oxygen is separated from the compound.

6. In the reactions given below, identify the process of prevention ofcorrosion.(a) Copper and zinc are mixed together in definite proportion to produce

brass.Ans. Allaying.

(b) Spoon made up of stailess steel is plated with silver usingelectrolysis.

Ans. Electroplating.(c) Iron nails are shining due to a coating of thing layer of zinc.

Ans. Galvanizing.(d) Copper is electrically coated with thin strong film of copper oxide.

Ans. Anodizing.(e) Cooking vessels made out of copper and brass are given kalhai

(coating of molten tin).Ans. Tinning.


SCHOOL SECTION 201

Air becomes liquid at about minus 190 degrees Celsius. Dynamite contains peanuts as an ingredient.

AMAZING FACTS

GLOSSARY

Element : It is a substance that cannot be broken downfurther into simpler substances.

Compound : When two or more elements combine in a fixedproportion.

Mixture : Combination of two or more substances thatare not chemically united and do not exist infixed proportions to each other.

PVC (polyvinyl chloride) : The electric wires that carry current in ourhomes have a covering of plastic called as PVC.

Electrostatic force of attraction : A strong force of attraction between particlesof opposite charges.

Tensile strength : It is the maximum stress that a material canwithstand while being stretched or pulled.

Density : Mass per unit volume.Melting point : The melting point of a solid is the temperature

at which it changes state from solid to liquid.Boiling point : The temperature at which the vapour pressure

of the liquid equals the environmentalpressure surrounding the liquid.

Alkali : Soluble bases which produce OH– ions inwater.

Oxidation : Addition of oxygen to a substance or removalof hydrogen from a substance.

Reduction : Addition of hydrogen to a substance or removalof oxygen from a substance.

Oxidising agent : The substance that gives oxygen for oxidationOR the substance that removes hydrogen.

Reducing agent : The substance that gives hydrogen forreduction or the substance that removesoxygen.

Inorganic : Considered to be of a mineral, not biologicalorigin.

Electrolytic reduction : Electrolytic reduction is the process ofreducing the oxides of metals to their pureform as metals.

Ion : Ion is an atom or group of atoms which is eitherpositively charged or negatively chargedformed due to loss or gain of electrons.

Cations : Positively charged ions are cations.Anions : Negatively charged ions are called as anions.

Q.I [A] Fill in the blanks : 11. ....................... is the only non-metal in liquid state.2. Aluminium oxide is ....................... in nature.

Q.I [B] Match the columns : 2Column A Column B

1. Sodium meta aluminate (a) NaAlO2 or Na2Al2O4

2. Sodium oxide (b) Ca(OH)2

3. Calcium hydroxide (c) Na2O4. Copper sulphate (d) CuSO4

Q.I [C] State whether True or False : 11. Silver and gold react with dilute acids.2. Most metal oxides are insoluble in water.

Q.I [D] Find odd man out : 11. K2O, Na2O, Al2O3, CaO.2. Brass, Bronze, Steel, Antimony.

Q.I [E] Give the configurations of the following : 11. Chlorine.2. Potassium.

Q.II [A] Give scientific reasons : (Any Two) 41. Sodium and potassium is stored under kerosene.2. Sodium and chlorine are poisonous substances but sodium chloride

is edible.3. Elements like gold, silver are used to make jewellery.

Q.II [B] Distinguish between : 21. Metals and Non-metals.2. Calcination and Roasting.

CHAPTER 8 : UNDERSTANDING METALS AND NON METALS

S.S.C.

SCIENCE

Marks : 30

Duration : 1 hr.

Q.III Explain the following chemical reactions with the help of 6balanced equation : (Any Three)

1. Aluminium reacts with steam.2. Iron filings are sprinkled in the flame of the burner.3. Sodium reacts with oxygen.4. Magnesium reacts with dilute hydrochloric acid.5. Zinc carbonate is heated in limited supply of air.

Q.IV [A] Draw neat and labelled diagram : (Any One) 21. Electrolytic reduction of alumina.2. Formation of sodium chloride.

Q.IV [B] Answer the following in one sentence each : : (Any Four) 41. Name the element that has the highest melting point.2. Name some metals used for cooking purposes.3. Name the metals that can be cut easily with a knife.4. Name the non-metal that is a good conductor of electricity.5. Name the metals that are the best conductors of heat.

Q.V [A] Answer the following in brief : (Any One) 41. What is corrosion and explain the methods to prevent corrosion.2. Explain the properties of ionic compounds.

Q.V [B] Answer the following in short : (Any One) 21. Metal A has electronic configuration of 2, 8, 1 and metal B has 2, 8,

8, 2 which is more reactive. Identify these metals and give theirreactions with dil. HCl.

2. What is an alloy and give two examples.

... 2 ...

Best Of Luck

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Understanding Metals 8. and Non Metalsmt-iconnect.com/MTE_Content/MTE/Notes_Question... · Silver is the best conductor of electricity and next in order is copper. ... They react