Question

The number of non-ionisable hydrogen atoms present in the final product obtained from the hydrolysis of PCl\(_5\) is :

• A. 1
• B. 2
• C. 3
• D. 0

Hint:

For phosphorus oxyacids, remember the rule for basicity (number of ionisable H atoms):
H\(_3\)PO\(_4\) (Phosphoric acid): All 3 H are on O atoms. Basicity = 3.
H\(_3\)PO\(_3\) (Phosphorous acid): 2 H are on O atoms, 1 H is on P.
Basicity = 2.
H\(_3\)PO\(_2\) (Hypophosphorous acid): 1 H is on an O atom, 2 H are on P. Basicity = 1.
Only hydrogens attached to oxygen are acidic.

Answer 1

The Correct Option is D

To solve the problem, we need to understand the hydrolysis reaction of phosphorus pentachloride (PCl\(_5\)).

PCl\(_5\) when hydrolyzed generates phosphorus oxychloride (POCl\(_3\)) initially as an intermediate and then further reacts to form orthophosphoric acid (H\(_3\)PO\(_4\)). The complete hydrolysis reaction can be written as follows:

\text{PCl}_5 + 4\text{H}_2\text{O} \rightarrow \text{H}_3\text{PO}_4 + 5\text{HCl}

Orthophosphoric acid, H\(_3\)PO\(_4\), is the final product obtained in this reaction. In order to find the number of non-ionisable hydrogen atoms, let's look at the structure and ionization of phosphoric acid:

• The molecular structure of H\(_3\)PO\(_4\) consists of three hydroxyl groups (-OH) attached to the phosphorus atom.
• All hydrogen atoms in the hydroxyl groups are ionisable in the form of releasing protons (H\(^+\)).

Thus, when examining the structure of ortho-phosphoric acid (H\(_3\)PO\(_4\)), all hydrogen atoms are positioned such that they can be released in solution as ions. Therefore, there are no non-ionisable hydrogen atoms in orthophosphoric acid.

Therefore, the number of non-ionisable hydrogen atoms present in the final product of the hydrolysis of PCl\(_5\) is:

• 0

This confirms the correct answer is indeed: 0.