Question

Sulphuryl chloride $S{{O}_{2}}C{{l}_{2}}$ reacts with water to get a mixture of ${{H}_{2}}S{{O}_{4}}$ and HCl. Number of moles of NaOH required to neutralize the solution formed by adding 1mol of $S{{O}_{2}}C{{l}_{2}}$ to excess water is:
[A] 1
[B] 2
[C] 3
[D] 4

Answer 1

Hint: A neutral solution means it will have equal number of hydrogen ions and hydroxyl ions. By finding the number of moles of acid formed after the reaction, we can find the number of hydrogen ions in the solution and hence the same number of hydroxyl ions needed to neutralize the solution.

Complete step-by-step answer: As the question says, sulphuryl chloride reacts with water and gives us a mixture of sulphuric acid and hydrochloric acid. We can write the reaction after balancing as-
\[S{{O}_{2}}C{{l}_{2}}+2{{H}_{2}}O\to {{H}_{2}}S{{O}_{4}}+2HCl\]
One mole of sulphuric chloride reacts with two moles of water and gives us one mole of sulphuric acid and two moles of hydrochloric acid.
As we know, acids are proton donors i.e. they can donate their hydrogen ions to bases in a reaction.
Sodium hydroxide is a base which means it will accept the protons.
As we know, to neutralize a solution we need to have an equal number of hydrogen ions, ${{H}^{+}}$ and hydroxyl ions, $O{{H}^{-}}$. When these two are equal, the solution is neutral which means that the solution is neither acidic nor basic.
In the above reaction as we can assume from their formulas, sulphuric acid is a dibasic acid which means it has two hydrogen ions to donate to a base whereas hydrochloric acid is monobasic acid as it has only one hydrogen ion to donate to a base.
In the reaction, we have one mole of sulphuric acid and two moles of hydrochloric acid.
Therefore, we have one mole of sulphuric acid which gives us two hydrogen ions in the reaction and two moles of hydrochloric acid which gives us one hydrogen ion each i.e. two more hydrogen ions in the solution.
Therefore, there are a total of four hydrogen ions in the solution.
To neutralize this solution, we have to add equal moles of hydroxyl ions
And one mole of sodium hydroxide will give us one hydroxyl ion.
Therefore, to neutralize four hydrogen ions, we need four hydroxyl ions and therefore, four moles of sodium hydroxide i.e. 4 moles of NaOH required to neutralize the solution formed by adding 1 mol of $S{{O}_{2}}C{{l}_{2}}$ to excess water.
Therefore, the correct answer is option [D] 4.

Note: A solution having excess hydroxyl ions is a base and a solution having excess hydrogen proton is an acid. Having equal numbers of hydroxyl ions and hydrogen ions will make it neutral because it will have no electrical charge.