(a) When carbon is heating with concentrated sulphuric acid, carbon dioxide is formed. Why?
(b) Why the wooden shelves on which concentrated sulphuric acid bottles are kept are stained black? [4 MARKS]

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Solution

Each option: 2 Marks

(a) Hot concentrated sulphuric acid acts as a powerful oxidising agent and decomposes giving nascent oxygen which helps in oxidation of carbon dioxide and in turn gets itself reduced to $S O_{2}$ .
(b) The wooden shelves on which concentrated $H_{2} S O_{4}$ acid bottles are kept become black because cellulose present in wood reacts with concentrated $H_{2} S O_{4}$ forming a charred black spongy mass of carbon.

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Give reasons for the following:
(i) In the contact process, sulphur trioxide formed is dissolved in 98% sulphuric acid and not in water.
(ii) When solution of sulphur dioxide is exposed to air, it gets converted to sulphuric acid.
(iii) When diluting concentrated sulphuric acid, the acid should be added to water and not water to the acid.
(iv) When concentrated sulphuric acid is exposed to air, its volume increases and it becomes slightly dilute.
(v) Sulphuric acid can form two kinds of salts with sodium chloride.
(vi) When barium chloride is added to dilute sulphuric acid, a white precipitate is formed.
(vii) When carbon is heated with concentrated sulphuric acid, carbon dioxide is formed.
(viii) Ammonia gas cannot be dried by passing through concentrated sulphuric acid.
(ix) When concentrated sulphuric acid is added to sugar/glucose, a black mass is left behind.
(x) Concentrated sulphuric acid should not be added to oxalic acid or formic acid in the open laboratory.
(xi) When concentrated sulphuric acid is added to blue crystalline copper sulphate, it turns powdery white.
(xii) Concentrated sulphuric acid must be stored in airtight bottles.
(xiii) Cotton clothes get burnt with concentrated sulphuric acid.
(xiv) H₂SO₄ cannot be prepared by heating sodium sulphate with conc. HCl or HNO₃.

Q. Explain why [4 MARKS]
(a) Only all-glass apparatus should be used for the preparation of nitric acid by heating concentrated sulphuric acid and potassium nitrate.
(b) Nitric acid, when kept in a reagent bottle for a long time, turns yellow.

Q. Give reasons for the following:
(a) Sulphuric acid forms two types of salts with NaOH.
(b) Red-brown vapours are produced when concentrated sulphuric acid is poured on it
(c) A piece of wood becomes black when concentrated sulphuric acid is poured on it.
(d) Brisk effervescence is seen when oil of vitriol is added to sodium carbonate.
[4 MARKS]

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(ii) What property of sulphuric acid is shown by the reaction of concentrated sulphuric acid when heated with
(A) potassium nitrate (B) carbon? [5 MARKS]

Q. Why does sulphur on reacting with concentrated nitric acid gives sulphuric acid instead of sulphur dioxide?

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(a) When carbon is heating with concentrated sulphuric acid, carbon dioxide is formed. Why? (b) Why the wooden shelves on which concentrated sulphuric acid bottles are kept are stained black? [4 MARKS]

(a) When carbon is heating with concentrated sulphuric acid, carbon dioxide is formed. Why?
(b) Why the wooden shelves on which concentrated sulphuric acid bottles are kept are stained black? [4 MARKS]