Chemistry Class-X 1 Question Bank

Question Bank

Sulphur Dioxide and Sulphuric Acid

1. Write equations for the preparation of sulphur dioxide gas from : (i) sodium sulphite (ii) sodium bisulphite [2] Ans. (i) Na2SO3 + H2SO4 (dil.) ⎯⎯→ Na2SO4 + H2O + SO2 (ii) 2NaHSO3 + H2SO4 (dil.) ⎯⎯→ Na2SO4 + 2H2O + 2SO2 2. Write equation for the preparation of sulphur dioxide from conc. sulphuric acid and copper. [1] Ans. When copper turnings are boiled with conc. sulphuric acid, sulphur

dioxide gas is evolved. Cu + 2H2SO4 (conc) boiled⎯⎯⎯→ CuSO4 + 2H2O + SO2 (g) 3. State with reasons how sulphur dioxide gas dried. Ans. Sulphur dioxide gas is dried by passing it through conc. sulphuric acid.

It is because conc. sulphuric acid has a very strong affinity for water and reacts with it to form sulphuric hydrate.

H2SO4 + H2O –→ H2SO4. H2O 4. How can you obtain sulphur dioxide from (i) sulphur (ii) ZnS and (iii) FeS2 [3] Ans. (i) By burning sulphur in air or oxygen, sulphur dioxide gas is

formed. S + O2

burning⎯⎯⎯→ SO2 (ii) By roasting zinc sulphide in air, sulphur dioxide gas in formed. 2ZnS + 3O2 roasting⎯⎯⎯→ 2ZnO + 2SO2 (iii) By roasting FeS2 in air sulphur dioxide gas is formed 4FeS2 +11O2 roasting⎯⎯⎯→ 2Fe2O3 + 8SO2 5. State two properties of sulphur dioxide which lead to its storage in

large volumes. Ans. (i) It liquifies at –10°C (ii) It liquefies under a pressure of two atmospheres.

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6. By writing the chemical equations, name the acid obtained when (a)

sulphur dioxide (b) sulphur trioxide is dissolved in water. [2] Ans. (a) Sulphurous acid is obtained SO2 + H2O —→ H2SO3

(b) Sulphuric acid obtained SO3 + H2O —→ H2SO4

7. Name a gas which is called acid anhydride of sulphurous acid. Give one reason.

Ans. The gas is sulphur dioxide. It is because when sulphurous acid loses water it forms sulphur dioxide

gas. H2SO3 — H2O —→ SO2 8. How will you obtain (a) normal salt (b) an acid salt, starting from

sodium hydroxide and sulphur dioxide? Ans. (a) When limited amount of SO2 gas is passed through sodium

hydroxide solution normal salt (sodium sulphite) is formed 2NaOH + SO2 Na2SO3 + H2O (b) When excess of SO2 gas is formed through sodium hydroxide

solution an acid salt (sodium bisulphite) is formed. NaOH + SO2 –→ NaHSO3 9. Name two gas which on passing through lime water, trun it milky. Write chemical equations in support of your answer. [3] Ans. (i) CO2 : Ca(OH)2 + CO2 —→ CaCO3 + H2O (ii) SO2 : Ca(OH)2 + SO2 —→ CaSO3 + H2O 10. By stating type of reaction and chemical equation, state, how sulphur dioxide gas reacts with (i) dry chlorine (ii) chlorine water. [4] Ans. (i) Sulphur dioxide reacts with moist chlorine to form sulphuryl

chloride. It is an addition reaction. SO2 + Cl2 —→ SO2Cl2

(ii) Sulphur dioxide reacts with moist chlorine to form a mixture of sulphuric acid and hydrochloric acid. It is a reduction reaction of sulphur dioxide.

SO2 + Cl2 + 2H2O —→ 2HCl + H2SO4

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11. By writing equations, state two oxidising reactions of sulphur dioxide.

Name the product of oxidation. Ans. (i) Sulphur dioxide reacts with burnning magnesium to form

magnesium oxide and sulphur. The product of oxidation is magnesium oxide.

2Mg + SO2 burning⎯⎯⎯→ 2MgO + S (ii) Sulphur dioxide oxidises hydrogen sulphide solution to form

water and sulphur. 2H2S + SO2 —→ 2H2O + 3S

12. Write chemical equations for the reaction of sulphur dioxide with (i) Fe2 (SO4)3 sol. (ii) FeCl3 (sol) Ans. (i) Fe2(SO4)3 + SO2 + 2H2O —→ 2FeSO4 + 2H2SO4 (ii) 2FeCl3 + SO2 + 2H2O —→ 2FeCl2 + H2SO4 + 2HCl 13. State what will you observe and write chemical equations when sulphur dioxide gas is passed through aqueous and acidified

solution of (a) KMnO4 (b) K2Cr2O7. [4] Ans. (a) The pink coloured KMnO4 solution is decolourised

2KMnO4 + 2H2O + 5SO2 —→ K2SO4 +2MnSO4 + 2H2SO4 (b) The orange coloured K2Cr2O7 solution changes to green colour due to the formation of Cr2(SO4)3

K2Cr2O7 + H2SO4 + 3SO2 —→ K2SO4 + Cr2(SO4)3 + H2O 14. Why is bleaching of colouring matter by sulphur dioxide is termed as reduction reaction? Ans. Sulphur dioxide reacts with water (moisture) to form nascent hydrogen, which removes oxygen atoms from colouring matter and hence the bleaching is a reduction reaction.

2H2O + SO2 —→ H2SO4 + 2(H) Colouring matter + 2(H) —→ colourless product + water

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15. State two differences between the bleaching action of sulphur dioxide and chlorine. [2] Ans. (i) Bleaching done by sulphur dioxide is due to the reduction process, whereas bleaching done by chlorine is due to oxidation process. (ii) Bleaching done by sulphur dioxide is temporary in nature, whereas bleaching done by chlorine is permanent in nature. 16. Write fully balanced equations when : (i) FeS2 (iron pyrites) is heated in air. (ii) Copper turnings are heated with concentrated sulphuric acid. (iii) Potassium bisulphite is treated with dilute hydrochloric acid. (iv) Sulphur is burnt in air or oxygen. [4] Ans. (i) 4FeS2 + 11O2 burning⎯⎯⎯→ 2Fe2O3 + 8SO2 (ii) Cu + 2H2SO4 heat⎯⎯⎯→ CuSO4 + 2H2O + SO2 (iii) KHSO3 + HCl (dil.) —→ KCl + H2O + SO2 (iv) S + O2 —→ SO2 (main reaction) 2S + 3O2 —→ 2SO3 (minor reaction) 17. When sulphur is burnt in air, the gas so formed strongly fumes in

moist air. Explain your answer. Write chemical equations. [2] Ans. Sulphur on burning in air forms sulphur dioxide and traces of sulphur trioxide. Sulphur trioxide dissolves in the water vapour present in air to form sulphuric acid mist which appears in the form of fumes.

2S + 3O2 —→ 2SO3 SO3 + H2O (water vapour) —→ H2SO4 (sulphuric acid mist)

18. Why is bleaching done by sulphur dioxide temporary in nature? [2] Ans. The sulphur dioxide brings about bleaching by reduction, i.e., it removes oxygen atoms. The lost oxygen atoms are regained from atmosphere, over the passage of time, and hence the bleached clothes tend to regain colour.

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19. Write chemical equations for obtaining the following from dil. sulphuric acid. (a) Hydrogen (b) Carbon dioxide (c) sulphur dioxide (d) Hydrogen sulphide (e) a normal salt (f) an acid salt [6] Ans. (a) Zn + dil. H2SO4 –→ ZnSO4 + H2S (b) Na2CO3 + dil. H2SO4 –→ Na2SO4 + H2O + CO2 (c) Na2SO3 + dil. H2SO4 –→ Na2SO4 + H2O + SO2 (d) FeS + dil. H2SO4 –→ FeSO4 + H2S (e) 2NaOH + dil. H2SO4 –→ Na2SO4 + 2H2O (f) NaOH + dil. H2SO4 –→ NaHSO4 + H2O 20. Write chemical equations for the conc sulphuric acid when the products of oxidation are : (i) carbon dioxide (ii) sulphur dioxide (iii) copper sulphate (iv) sulphur

Ans. (i) C + 2H2SO4(conc.) heat⎯⎯⎯→ CO2 + 2H2O + 2SO2 (ii) S + 2H2SO4 (conc.) heat⎯⎯⎯→ 2SO2 + 2H2O (iii) Cu + 2H2SO4 (conc.) heat⎯⎯⎯→ CuSO4 +2H2O + SO2 (iv) H2S + H2SO4 –→ 2H2O + SO2 + S

21. State, how barium chloride solution and lead nitrate solution is used for testing the presence of sulphate ion in sulphuric acid. Write

relevant chemical equation. [5] Ans. (i) Barrium chloride solution on treating with dilute sulphuric acid

forms white ppt. of barium sulphate, which is insoluble in all acids.

BaCl2 + H2SO4 –→ 2HCl + BaSO4 (white ppt) (ii) Lead nitrate on treating with dilute sulphuric acid forms white

ppt of lead sulphate, which is insoluble in all acids. Pb (NO3)2 + H2SO4 (dil.) –→ 2HNO3 + PbSO4 (white ppt)

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22. How does hydrogen sulphide forms the following : (i) Lead sulphide (ii) zinc sulphide (iii) silver sulphide

(iv) copper sulphide Give the colour of sulphides and write relevant chemical equations. [8] Ans. (i) When hydrogen sulphide gas is passed through acidified lead

nitrate solution it forms black ppt of lead sulphide. Pb(NO3)2 + H2S –→ 2HNO3 + PbS (Black ppt) (ii) When hydrogen sulphide gas in passed through ammonical zinc

sulphate solution, it forms white gelatin like ppt. of zinc sulphide.

ZnSO4 + H2S –→ H2SO4 + ZnS (white ppt.) (iii) When hydrogen sulphide gas is passed through acidified silver

nitrate solution, it forms black ppt. of silver sulphide. 2AgNO3 + H2S –→ 2HNO3 + Ag2S (black ppt.) (iv) When hydrogen sulphide gas is passed through acidified copper

sulphate solution, it forms black ppt. of copper sulphide CuSO4 + H2S –→ H2SO4 + CuS (black ppt.) 23. Select the correct answer from choices in brackets. (i) The reduced product obtained when hydrogen sulphide reacts

with conc. sulphuric acid is __________ [SO2 /S/H2O]. (ii) The dehydrated product obtained when sugar reacts with conc.

sulphuric acid is __________ [CO2 /CO/C]. (iii) The salt which reacts with dil. sulphuric acid to form insoluble

ppt is __________ [Pb(NO3 )2 /NaNO3 /Cu(NO3 )2 ]. (iv) The oxidised product obtained when sulphur reacts with conc. sulphuric acid is __________ [H2 SO3 /H2 S/SO2 ]. (v) The type of salt formed when excess of caustic soda reacts with sulphuric acid is __________ [normal salt/acid salt]. [5]

Ans. (i) Sulphur (S) (ii) Carbon (iii) Lead nitrate [Pb(NO3)2] (iv) Sulphur dioxide (SO2) (v) Normal salt

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24. Write balanced equations for the following reactions. (i) Formation of an acid salt from sulphuric acid by a sodium salt. (ii) Formation of black spot on a piece of wood due to conc.

sulphuric acid. (iii) Formation of sulphur dioxide gas using a metal below hydrogen

in activity series. (iv) Oxidation of a fowl smelling gas by conc. sulphuric acid. (v) Formation of CO and CO2 by using conc. sulphuric acid. Ans. (i) NaCl + H2SO4 200 °C<⎯⎯⎯⎯→ NaHSO4 + HCl (ii) (C6H10O5)n + 5(H2SO4)n –→ 6Cn + 5(H2SO4.H2O) (iii) Cu + 2H2SO4 (conc.) heat⎯⎯⎯→ CuSO4 + 2H2O + SO2 (iv) H2SO4 + H2S –→ 2H2O + SO2 + S COOH (v) | +H2SO4 –→ CO +CO2 + H2SO4.H2O COOH 25. State whether the following reactions are

addition/reduction/oxidation/reactions : (i) Acidified potassium dicromate to chromium sulphate. (ii) Chlorine to sulphuryl chloride. (iii) Hydrogen sulphide to sulphur. (iv) Iron (III) sulphate to iron (II) sulphate. (v) Chlorine water to hydrochloric acid. Ans. (i) Reduction reaction (ii) Addition reaction (iii) Oxidation reaction (iv) Reduction reaction (v) Oxidation reaction. 26. (a) How is sulphuric acid prepared industrially by contact process?

Support your answer by writing fully balanced chemical equations.

(b) Why is sulphur trioxide formed in this process not absorbed directly in water?

(c) Why is vanadium pentoxide considered a better catalyst than platinised asbestos?

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(d) Why is heating of catalyst discontinued the moment when the

oxidation of sulphur dioxide takes place? [2 each] Ans. (a) Contact process for the manufacture of sulphuric acid : (i) Pure sulphur is burnt in excess of oxygen in sulphur burners

to form a mixture of sulphur dioxide and oxygen. The mixture is cooled and then washed with water to remove any dust particles as impurity.

S + O2 —→ SO2 The moist mixture is dried in conc. sulphuric acid and then

passed through arsenic purifier, so as to remove any arsenious oxide present in it. The purified mixture is then passed through testing box.

(ii) The purified mixture is finally introduced into catalytic oxidation chamber which contains a series of vertical tubes filled with vanadium pentoxide or platinised asbestos. Sulphur dioxide on coming in contact with catalyst is oxidised to sulphur trioxide.

2SO2 + O2 2 5V Oat 450 °C⎯⎯⎯⎯→ 2SO3

(iii) The sulphur trioxide gas is then absorbed in conc. sulphuric acid to form pyrosulphuric acid or oleum.

SO3 + H2SO4 (conc.) —→ H2S2O7 (iv) The pyrosulphuric acid is treated with calculated amount of

water to form conc. sulphuric acid. H2S2O7 + H2O —→ 2H2SO4

(b) It is because sulphur trioxide dissolves in water, producing a large amount of heat which changes sulphuric acid to sulphuric acid mist. The latter is very difficult to liquefy.

(c) Vanadium pentoxide does not get poisoned easily as compared to platinised asbestos, if the mixture of sulphur dioxide and oxygen is slightly impure.

(d) The reaction between sulphur dioxide and oxygen is exothermic in nature. Thus, once the reaction starts, it proceeds with its own heat.

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27. Explain the following : (1) Why are the wooden shelves on which concentrated sulphuric

acid bottles kept, stained black? [2] (2) Why is concentrated sulphuric acid always added to water and

not the water to concentrated sulphuric acid? Why does the mixture get hot? [3]

Ans. (1) Sulphuric acid (concentrated) is a very powerful dehydrating agent. It removes atoms of hydrogen and oxygen in the form of water from the cellulose [(C6H10O5)n], leaving behind carbon. It is black carbon which appears in the form of black stains. (2) In former case, the heat liberated is absorbed by large amount of water, as water has the highest specific latent heat capacity. Thus, no spurting takes place.

However, in the latter case, the small amount of water on entering in large amount of conc. sulphuric acid produces very large amount of heat which changes water into steam. Thus, sulphuric acid spurts. The heat is produced because water reacts with conc. sulphuric acid and the reaction is exothermic.

H2SO4 + H2O → H2SO4·H2O + Heat 28. What will you observe when concentrated sulphuric acid is poured on (i) sugar crystals (ii) copper sulphate crystals? [2] Ans. (i) The sugar crystals initially turn brown and the reaction mixture

starts frothing. It gives off large amount of steam and leaves behind a black porous spongy mass.

(ii) The blue coloured copper sulphate crystals gradually crumbles to form white powdery mass. The reaction mixture gets hot and sometimes starts boiling giving large amount of heat.

29. (a) An important industrial reaction is represented by the equation 2SO2 + O2 → 2SO3. The formation of sulphur trioxide is exothermic. State the conditions of temperature and state the name of catalyst required for the above reaction to take place. [3]

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(b) Describe the change you would observe : (i) When concentrated sulphuric acid is added to sugar. (ii) When concentrated sulphuric acid is added to formic acid,

HCOOH, and warmed. (iii) When burning magnesium is introduced into a gas jar

containing sulphur dioxide. Name the products formed and write an equation for the reaction.

(iv) In what capacity is sulphur dioxide acting? [4] Ans. (a) (i) The mixture of SO2 and O2 should be in the ratio of 2 : 1 by

volume and free from all impurities. (ii) A catalyst should be used. Platinised asbestos or

vanadium pentoxide are the catalysts. (iii) The temperature should be maintained at 450 °C. (b) (i) A porous black mass is formed.

C12H22O11 + 11H2SO4 → 12C + 11H2SO4.H2O (ii) Formic acid gets dehydrated with the liberation of carbon

monoxide gas. The reaction mixture gets hot. HCOOH + H2SO4 (conc.) → CO + H2SO4·H2O + Heat

(iii) Magnesium continues burning with the formation of a mixture of magnesium oxide and magnesium sulphide.

3Mg + SO2 → MgS + 2MgO + Heat (iv) In the above reaction, sulphur dioxide is acting as an

oxidising agent. 30. (a) A mixture of iron dust (iron fillings) and sulphur was heated.

The black solid residue M reacts with dilute sulphuric acid to give a foul smelling gas N. N when ignited burned with a blue flame and deposited a yellow residue O. On passing N into lead (II) nitrate solution, it gave a black precipitate P and a colourless solution Q. Name the substances M, N, O, P and Q and write an equation for each. [5]

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(b) Concentrated sulphuric acid (i) has a great affinity for water (ii)

is an oxidising agent (iii) is least volatile acid (iv) is dibasic acid. Give one reaction each with equation to show these properties of sulphuric acid. [5]

Ans. (a) M is iron (II) sulphide Fe + S —→ FeS N is hydrogen sulphide gas FeS + H2SO4 (dil.) → FeSO4 + H2S O is sulphur 2H2S + O2 —→ 2H2O + 2S P is lead sulphide Pb (NO3)2 + H2S —→ 2HNO3 + PbS (Black) Q is dilute nitric acid (b) (i) Conc. sulphuric acid dehydrates sugar. C12H22O11 + 11H2SO4 —→ 12C + 11H2SO4·H2O (ii) Conc. sulphuric acid oxidises carbon to CO2. C + 2H2SO4 —→ CO2 + 2H2O + 2SO2 (iii) Conc. sulphuric acid liberates nitric acid on boiling with

KNO3. 2KNO3 + H2SO4 —→ K2SO4 + 2HNO3 (iv) Dilute sulphuric acid forms two series of salts. NaOH + H2SO4 —→ NaHSO4 + H2O 2NaOH + H2SO4 —→ Na2SO4 + 2H2O 31. How would you distinguish between sulphur dioxide gas and

hydrochloric acid gas? [2] Ans. (i) Test each of the gases with acidified potassium dichromate

solution. In case of SO2, potassium dichromate solution turns green, but no action takes place in case of HCl gas.

(ii) Test each of the gases, with a rod dipped in ammonia solution. In case of HCl gas, dense white fumes are formed, but no action takes place in case of sulphur dioxide gas.

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32. (a) Both ammonia and sulphur trioxide are manufactured by

catalysed reaction of gases. Give an equation for each of these reactions and name the catalyst used in each case. [2]

(b) Give two household uses of ammonia. [2] (c) Describe in outline the chemistry of the manufacture of sulphuric

acid from sulphur by contact process. (No technical details required but equations should be given for each stage of process.) [3]

(d) What property of sulphuric acid is made use in each of the following cases? Give an equation for reaction in each case :

(i) Production of hydrogen chloride gas when it reacts with a chloride (say sodium chloride).

(ii) In the preparation of carbon monoxide gas from formic acid. (iii) As a source of hydrogen by diluting it and adding a strip of

magnesium. (iv) In the preparation of sulphur dioxide by warming a mixture

of concentrated sulphuric acid and copper turning. [4] Ans. (a) N2 + 3H2

Fe + Mo at 450 °C

200 atms – 900 atms⎯⎯⎯⎯⎯⎯→←⎯⎯⎯⎯⎯ 2NH3

Iron is the catalyst. 2SO2 + O2 2 5V O – 450 °C⎯⎯⎯⎯⎯→ 2SO3 V2O5 is the catalyst. (b) (i) Ammonia is used as a smelling liquid during common cold. (ii) Ammonia is used to remove grease stains from woollens. (c) Contact process for the manufacture of sulphuric acid : (i) Pure sulphur is burnt in excess of oxygen in sulphur burners

to form a mixture of sulphur dioxide and oxygen. The mixture is cooled and then washed with water to remove any dust particles as impurity.

S + O2 —→ SO2 The moist mixture is dried in conc. sulphuric acid and then

passed through arsenic purifier, so as to remove any arsenious oxide present in it. The purified mixture is then passed through testing box.

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(ii) The purified mixture is finally introduced into catalytic

oxidation chamber which contains a series of vertical tubes filled with vanadium pentoxide or platinised asbestos. Sulphur dioxide on coming in contact with catalyst is oxidised to sulphur trioxide.

2SO2 + O2 2 5V Oat 450 °C⎯⎯⎯⎯→ 2SO3

(iii) Sulphur trioxide gas is then absorbed in conc. sulphuric acid to form pyrosulphuric acid or oleum.

SO3 + H2SO4 (conc.) —→ H2S2O7 (d) (i) Least volatile acid : 2NaCl + H2SO4 (conc.) —→ Na2SO4 + 2HCl (g) (ii) Dehydrating agent : HCOOH + H2SO4 (conc.) —→ CO(g) + H2SO4.H2O (iii) Acts as an acid : Mg + H2SO4 (dil.) —→ MgSO4 + H2(g) (iv) Acts as an oxidising agent : Cu + 2H2SO4 (conc.) —→ CuSO4 + 2H2O + SO2 (g) 33. (a) Both chlorine and sulphur dioxide bleach moist litmus paper.

How would you distinguish between these two gases by a chemical test?

(b) “Sulphur trioxide and water react to form sulphuric acid.” Sulphuric acid may act as each of the following :

(1) An acid, forming sulphates which are soluble in water. (2) A compound, forming sulphates which are insoluble in

water. (3) A dehydrating agent. (4) A drying agent. (5) An oxidising agent. Which ONE of the above properties 1 to 5 are shown by

sulphuric acid when : (i) concentrated sulphuric acid is added to sugar? (ii) dilute sulphuric acid reacts with lead nitrate? (iii) dilute sulphuric acid is added to sodium hydroxide solution?

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(iv) hydrogen sulphide gas is passed through concentrated sulphuric

acid? (c) “Sulphur dioxide acts as an oxidising agent and a reducing

agent.” Give one balanced equation for the reaction in which sulphur dioxide acts as :

(i) an oxidising agent (ii) a reducing agent. Ans. (a) Test each of the gases with moist acidified potassium

dichromate paper. In case of sulphur dioxide, paper turns green, but not in case of chlorine.

(b) (i) It acts as a dehydrating agent. (ii) It acts as a compound, forming sulphates which are insoluble

in water. (iii) It acts as an acid, forming sulphates which are soluble in

water. (iv) It acts as an oxidising agent. (c) (i) Oxidising agent :

SO2 (sol.) + 2H2S —→ 2H2O + 3S (ii) Reducing agent :

Fe2 (SO4)3 + 2H2O + SO2 —→ 2H2SO4 + 2FeSO4 34. (a) In contact process, sulphur dioxide can be oxidised to sulphur

trioxide in the presence of platinised asbestos, which acts as a catalyst. The reaction is exothermic. Explain what is meant by the terms in bold italics.

(b) Give examples of the use of sulphuric acid. (1) As an electrolyte in everyday use. (2) As non-volatile acid.

(3) As an oxidising agent. (c) Why is a black spongy mass formed when concentrated sulphuric

acid is added to sugar? (d) Silver cannot be used to prepare hydrogen from hydrochloric acid

or sulphuric acid. Why?

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Ans. (a) (i) Catalyst : It is a substance which alters the rate of chemical

reaction, without itself undergoing any chemical change. (ii) Oxidised : When a substance gains oxygen or electronegative

radical, it is said to be oxidised. (iii) Exothermic : A chemical reaction which proceeds with the

evolution of heat energy is called a exothermic reaction. (b) (1) Electrolyte for lead acid accumulators. (2) In the preparation of nitric acid and hydrochloric acid gas. (3) In the preparation of SO2 gas from copper turnings. (c) Sulphuric acid is a powerful dehydrating agent. It removes

hydrogen and oxygen atoms from the structure of sugar molecule (C12H22O11) in the form of water, leaving behind carbon, which appears in the form of black spongy mass.

(d) It is because the position of silver is lower in metal activity series in comparison to hydrogen. Thus, it cannot displace hydrogen from sulphuric acid or hydrochloric acid.

35. Explain, briefly how you will obtain sulphur dioxide gas from sodium sulphite.

Ans. Sodium sulphite is treated with dilute sulphuric acid, the reaction takes place at room temperature with the formation of sulphur dioxide gas.

Na2SO3 + H2SO4 (dil.) —→ Na2SO4 + SO2 + H2O The gas is dried by passing it through conc. sulphuric acid and

collected by downward displacement of gas. 36. (a) When blue copper sulphate crystals are added to concentrated

sulphuric acid, they turn white. Explain. [2] (b) Name a catalyst used in contact process for the manufacture of sulphuric acid. [2] (c) By describing one chemical test in each case explain, how you

will distinguish between sulphur dioxide gas and hydrochloric acid gas. [2]

(d) Give the formula of the substance which is responsible for tarnish on silver spoon. [1]

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(e) What is the name given to the salts of sulphurous acid? [1] (f) The contact process for making sulphuric acid can be outlined

with four equations. Write them down in order. [4] (g) Give two uses of sulphur dioxide. [2] (h) Sulphuric acid can behave : [2]

(i) as an acid; (ii) as a less volatile acid; (iii) as an oxidising agent; (iv) as a drying agent for certain gases. State in words, an example of each case.

Ans. (a) Refer to answer 28 (ii) — Section C. (b) Platinised asbestos or vanadium pentoxide. (c) Refer to answer 31 — Section C. (d) Silver (I) sulphide. [Ag2S]. (e) Sulphites and hydrogen sulphites (bisulphites). (f) S + O2 —→ SO2 2SO2 + O2 Pt – 450 °C⎯⎯⎯⎯→ 2SO3 SO3 + H2SO4 —→ H2S2O7 H2S2O7 + H2O —→ 2H2SO4 (g) Uses of sulphur dioxide : 1. It is used for bleaching delicate objects such as wool, silk,

feathers, etc. 2. It is used in bleaching cane juice in sugar mills. 3. It is used in the refining of kerosene oil. 4. It is used in the manufacture of sulphuric acid. 5. It is used in making industrial sulphites such as, sodium

hydrogen sulphite. (h) (i) Sulphuric acid acts as an acid because it reacts with metallic

hydroxides to form salt and water only. (ii) Sulphuric acid acts as less volatile acid because on heating

with potassium nitrate, the nitric acid distils over, but not sulphuric acid.

(iii) Sulphuric acid acts as an oxidising agent because on boiling with sulphur, it forms sulphur dioxide gas.

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(iv) Sulphuric acid acts as a drying agent, because it is a powerful

hygroscopic agent. 37. (a) Write down the word equations for each of the following

reactions : (i) Conc. sulphuric acid + Copper —→ (ii) Conc. sulphuric acid + Sodium chloride —→ (iii) Conc. nitric acid + Copper —→ (iv) Conc. hydrochloric acid + Manganese dioxide —→ (v) Sodium hydroxide solution + Zinc —→ [5] (b) What is the formula for anhydride of sulphuric acid ?

Ans. (a) (i) Conc. sulphuric acid + Copper —→ Copper sulphate + Water + Sulphur dioxide gas.

(ii) Conc. sulphuric acid + Sodium chloride —→ Sodium sulphate + HCl gas.

(iii) Conc. nitric acid + Copper —→ Copper nitrate + Nitrogen dioxide + Water.

(iv) Conc. hydrochloric acid + Manganese dioxide —→ Manganese chloride + Water + Chlorine.

(v) Sodium hydoxide solution + Zinc —→ Sodium zincate + Hydrogen.

(b) Acid anhydride of sulphuric acid is sulphur trioxide (SO3). 38. (a) State one similarity and three differences between bleaching

action of chlorine and sulphur dioxide gas. [5] (b) Sulphuric acid acts as (i) an acid (ii) an oxidising agent (iii) a

dehydrating agent (iv) less volatile acid. Give one reaction each to illustrate the above properties of

sulphuric acid. [5] Ans.(a) Both bleach animal and vegetable colouring matter when moist.

Differences : (i) Bleaching in case of chlorine is due to oxidation, whereas in

case of sulphur dioxide is due to reduction. (ii) Bleaching done by chlorine is permanent in nature, whereas that

of sulphur dioxide is temporary in nature.

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(iii) Bleaching done by chlorine damages delicate fibres like wool

and silk, but bleaching by sulphur dioxide does not cause damage.

(b) Refer to answer 32 (d) — Section C. 39. (a) Give one large scale use of sulphur. [2]

(b) Write balanced molecular equations for the laboratory preparation of :

(i) Sulphur dioxide from sodium sulphite. (ii) Chlorine by the oxidation of hydrochloric acid. (iii) Nitrogen from ammonium nitrite. [3] (c) (i) “Sulphur dioxide is a powerful reducing agent. But it also acts

as an oxidising agent”. State in words or give balanced equations of two such reactions in which it acts as an oxidising agent. [2]

(ii) Sulphurous acid is said to be a dibasic acid. What is meant by the term “dibasic”?

(d) (i) Calculate the vapour density of sulphur dioxide gas. (S = 32; O = 16)

(ii) Explain bleaching action of sulphur dioxide. (e) Distinguish between a drying agent and dehydrating agent. [2]

Ans. (a) It is used in the manufacture of sulphuric acid. (b) (i) Na2SO3 + H2SO4 (dil.) —→ Na2SO4 + H2O + SO2 (g) (ii) MnO2 + 4HCl (conc.) heat⎯⎯⎯→ MnCl2 + 2H2O + Cl2 (g) (iii) NH4NO2

Warm⎯⎯⎯→ N2 (g) + 2H2O (c) (i) 2H2S + SO2 (sol.) —→ 2H2O + 3S 3Mg + SO2 —→ 2MgO + MgS (ii) It means a molecule of sulphuric acid in aqueous solution can

furnish two hydrogen ions.

Chemistry Class-X 19 Question Bank

(d) (i) V.D. of SO2 = Molecular wt. ÷ 2 = 64 ÷ 2 = 32. (ii) Bleaching properties of sulphur dioxide are based on the fact

that, it easily liberates nascent hydrogen when treated with water. The nascent hydrogen reacts with oxygen atoms present in vegetable colouring matter and hence bleaches it.

SO2 + 2H2O —→ H2SO4 + 2 [H] Veg. colouring matter + 2 [H] —→ Colourless product + Water (e) Drying agent removes superfluous moisture sticking to a

substance, whereas dehydrating agent removes hydrogen and oxygen atoms in the form of molecules of water from the composition of a substance.

40. (a) Name all the products formed when : (i) copper is heated with conc. sulphuric acid. (ii) chlorine gas is passed through sulphurous acid. [2] (b) Write a balanced equation when sulphur dioxide gas is passed

through iron (III) chloride solution. [1] (c) What is the function of concentrated sulphuric acid in the

preparation of carbon monoxide from oxalic acid? [1] Ans. (a) (i) Products formed are copper sulphate, sulphur dioxide gas and

water. (ii) Products formed are sulphuric acid and hydrochloric acid. (b) 2FeCl3 + SO2 + H2O —→ H2SO4 + 2FeCl2 + 2HCl (c) Sulphuric acid acts as a dehydrating agent.

41. (a) In the manufacture of sulphuric acid by contact process, great care is taken to purify the mixture of air and sulphur dioxide, especially to free it from arsenic impurities. Explain. [2]

(b) Write balanced equations of the reactions in the preparation of the following : [3]

(i) ammonia from ammonium chloride. (ii) chlorine from bleaching powder. (iii) sulphur dioxide from sodium sulphite. (c) Give two large scale uses of sulphur dioxide [2]

Chemistry Class-X 20 Question Bank

(d) Whenever water is added to concentrated sulphuric acid or

concentrated sulphuric acid is added to water, a large amount of heat is liberated. But the acid dangerously spurts out only when water is added to the concentrated acid. Explain the above observation giving a reason. [4]

Ans. (a) It is because the catalyst gets poisoned in the presence of impurities like As2O3, H2S and dust particles. Thus, oxidation of SO2 gas does not take place.

(b) (i) 2NH4Cl + Ca(OH)2 —→ CaCl2 + 2H2O + 2NH3 (ii) CaOCl2 + 2HCl —→ CaCl2 + H2O + Cl2 (iii) Na2SO3 + H2SO4 (dil.) —→ Na2SO4 + H2O + SO2 (c) Uses of sulphur dioxide : 1. It is used for bleaching delicate objects such as wool, silk,

feathers, etc. 2. It is used in bleaching cane juice in sugar mills. (d) Refer to answer 27(2) — Section C.

42. (a) Concentrated sulphuric acid should be kept in air-tight bottles. [2] (b) Write a balanced equation for the preparation of sulphur dioxide

by the action of hot conc. sulphuric acid on sulphur. [1] (c) Give two large-scale uses of sulphur dioxide. [2] Ans. (a) Conc. sulphuric acid is highly hygroscopic in nature. Thus, it

absorbs large amount of moisture from air and changes to dilute form. Thus, it must be kept in air-tight bottles.

(b) S + 2H2SO4 (conc.) heat⎯⎯⎯→ 3SO2 (g) + 2H2O (c) Uses of sulphur dioxide : 1. It is used in the refining of kerosene oil. 2. It is used in the manufacture of sulphuric acid.

43. (a) A compound X is warmed with dil. sulphuric acid. It gives off a colourless gas which turns acidified potassium dichromate paper green. Name the anion present in the compound. [1]

Chemistry Class-X 21 Question Bank

(b) The following statements are correct only, under certain

conditions. Rewrite each of the statement, including appropriate condition (s) and underline them.

(i) Sulphur dioxide is a bleaching agent. (ii) Oxalic acid and sulphuric acid react to produce carbon

monoxide and carbon dioxide. [2] (c) Write an equation to show sulphur dioxide is an oxidising agent. [1] (d) 1. What is contact process employed for? 2. Name two gases which combine during the contact process. 3. Name the catalyst used in the contact process. 4. Write an equation between zinc and final product of the

contact process. [4] Ans. (a) Anion present is sulphite. (b) (i) Moist sulphur dioxide is a bleaching agent. (ii) Oxalic acid crystals and conc. sulphuric acid react to

produce carbon monoxide and carbon dioxide on heating. (c) 2H2S + SO2 (sol.) —→ 2H2O + 3S (d) 1. In the oxidation of sulphur dioxide to sulphur trioxide for the

manufacture of sulphuric acid. 2. Sulphur dioxide gas and oxygen gas. 3. Platinised asbestos or vanadium pentoxide. 4. Zn + H2SO4 (dil.) —→ ZnSO4 + H2 (g)

44. (a) (i) State your observations when a crystal of CuSO4· 5H2O is placed in concentrated sulphuric acid. State one reason for your observation.

(ii) Describe another way by which the same effect can be produced as in 44 (a).

(iii) What is the meaning of term “water of crystallisation?” [3] (b) (i) Name two acids which can be prepared by using sulphuric

acid? (ii) Which property of sulphuric acid is used in preparing acids,

named by you. [2]

Chemistry Class-X 22 Question Bank

(c) Write balanced equations for obtaining the following gases from

dilute sulphuric acid. (i) hydrogen (ii) carbon dioxide (iii) sulphur dioxide. [3] (d) (i) Write four balanced equations for the chemical reactions

taking place during contact process and name the catalyst. (ii) Name the another metal sulphide [excluding Iron pyrites]

which on roasting produces sulphur catalyst. [5] Ans. (a) (i) Refer to answer 28 (ii) — Section C (ii) By heating copper sulphate crystals strongly the same effect

is produced. (iii) The number of water molecules which crystallise with one

molecule of a salt from its saturated solution is called water of crystallisation.

(b) (i) Hydrochloric acid and nitric acid. (ii) Sulphuric acid is the least volatile acid. (c) (i) Mg + dil. H2SO4 —→ MgSO4 + H2 (g) (ii) Na2CO3 + dil. H2SO4 —→ Na2SO4 + H2O + CO2 (g) (iii) Na2SO3 + dil. H2SO4 —→ Na2SO4 + H2O + SO2 (g) (d) (i) S + O2 —→ SO2

2SO2 + O2 V O2 5at 450 °C

⎯⎯⎯⎯⎯→ 2SO3

SO3 + H2SO4 (conc.) —→ H2S2O7 H2S2O7 + H2O —→ 2H2SO4

(ii) Lead sulphide : 2PbS + 3O2 —→ 2PbO + 2SO2