Sulphuric acid $(H_{2} {SO}_{4})$ is a strong acid and is extremely useful both in the industry and in the laboratory. It forms two types of salts on reacting with a base. These are acid salts and normal salts. Care must be taken while diluting the acid with water. It is done by adding acid drop wise to water taken in a beaker and not water to the acid. If water is added to the acid taken in the beaker. How will you account for this observation?

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Solution

The observation when water is added to water is the production of a lot of heat accompanied by splashing out of the solution.
This observation can be explained as:-
Dilution of an acid is a highly exothermic reaction.
When water is added to the acid, all the acid is diluted simultaneously which produces a lot of heat.
Thus, always acid should be added dropwise in water.

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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. Indicate if the following statements are true or false.
(a) Oxides of non-metals dissolve in water to form some acids.
(b) Sulphites are salts formed from sulphuric acid.
(c) Phosphoric acid is tribasic.
(d) Nitric acid can only form normal salts.
(e) Hydrochloric acid can form both carbonates and bicarbonate.
(f) Carbonic acid can form both carbonates and bicarbonates.
(g) Water of crystallisation is found in anhydrous salts.
(h) Litmus turns red in the presence of alkalis.
(i) An acid reacts with a carbonate to form a salt, and hydrogen gas is obtained.
(j) Acid taste sweet.
(k) When the metal zinc reacts with hydrochloric acid, a salt called zinc chloride is formed.
(l) when metals react directly with acids, the reaction is called a displacement reaction.
(m) Sulphuric acid has the formula H₂SO₃.
(n) Carbon dioxide gas is given off as a result of displacement reactions between acids and metals.

Suppose, in your lab, you have run out of dilute Sulphuric acid. You require dilute $H_{2} S O_{4}$ for an important synthesis but only have concentrated Sulphuric acid, water and a glass beaker. How will you synthesize dilute $H_{2} S O_{4}$ ?

While diluting concentrated sulphuric acid, the water should be added to acids and not acid to the water.

Account for the following :
While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

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