Question

When oleum (${H_2}{S_2}{O_7}$) is completely hydrolyzed, then how many acidic hydrogens are present in the final product?
A.$2$
B.$3$
C.$4$

Answer 1

Hint:The contact process is the method to produce sulphuric acid at the high concentrations needed for industrial processes. Platinum was initially used as the catalyst for this reaction but vanadium (V) oxide (${V_2}{O_5}$) is now preferred.

Complete step by step solution:
Mostly sulphuric acid is formed by contact process.
The whole reaction is divided into five steps which are first conversion of sulphur into sulphur dioxide the sulphur dioxide to sulphur trioxide then sulphur trioxide to oleum and then at last oleum to sulphuric acid.
Complete steps to form sulphuric acid by Contact process is as follows:
Step (i) Solid sulphur is burned in air to form sulphur dioxide gas. The reaction is as follows:
$S + {O_2} \to S{O_2}$
Step (ii) The sulphur dioxide gas formed by the burning of sulphur in air is mixed with more air and then it is cleaned to remove the impurities.
Step (iii) The sulphuric acid with air is heated at high temperature i.e. ${450^ \circ }C$ and at pressure of $1 - 2atm$ in the presence of catalyst (which do not take part in the reaction but enhance the rate of reaction) vanadium ${V_2}{O_5}$. The product of this reaction is sulphur trioxide gas. The reaction is as follows: $2S{O_2} + {O_2} \to 2S{O_3}$
Step (iv) The formed sulphur trioxide gas is then reacted with sulphuric acid to form oleum also known as disulphuric acid. The reaction of sulphuric hydroxide wit sulphuric acid is as:
$S{O_3} + {H_2}S{O_4} \to {H_2}{S_2}{O_7}$.
Sulphuric acid is used in the reaction because if we use water instead of sulphuric acid then the reaction will produce sulphuric acid but the rate of this reaction is very slow. So to increase the rate of reaction we use sulphuric instead of water.
Step (v) Water is added to disulphuric acid or oleum which forms sulphuric acid as a product. The reaction is:
${H_2}{S_2}{O_7} + {H_2}O \to 2{H_2}S{O_4}$.
Here in the product we get two moles of sulphuric acid. And also we know that one mole of sulphuric acid has two acidic hydrogen hence the product will have four acidic hydrogens.

Hence, option C is correct.

Note:
Catalyst: these are those molecules or atoms which do not take part in the reaction but can enhance (either increase or decrease) the rate of reaction. The catalysts which increase the rate of reaction are known as positive catalysts and the catalysts which decrease the rate of reaction are known as negative catalysts.