Why does a piece of cotton cloth get charred when immersed in concentrated sulphuric acid?

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Solution

Concentrated sulphuric acid is a very strong dehydrating agent. It dehydrates the cellulose fibers in cotton cloth, thereby charring them.

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Similar questions

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

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 added to hydrogen bromide,

(d) Brisk effervescence is seen when oil of vitriol is added to sodium carbonate.

Q. When ethanol is heated with excess of concentrated sulphuric acid at

170^{o} C

, it gets converted to ethene. In this reaction, concentrated sulphuric acid acts as:

Q. (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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