Question

Which one of the following oxoacids of phosphorus can reduce AgNO₃ to metallic silver ?

• A. H₃PO₂
• B. H₄P₂O₇
• C. H₄P₂O₆
• D. H₃PO₄

Answer 1

The Correct Option is A

The correct answer is Option 1: H₃PO₂.

To reduce AgNO₃ to metallic silver, the oxoacid of phosphorus must have a reducing property. Let's analyze the given options:

• H₃PO₂ (Hypophosphorous acid): This acid is a strong reducing agent.
• H₄P₂O₇ (Pyrophosphoric acid): This acid is not a strong reducing agent.
• H₄P₂O₆ (Hypophosphoric acid): This acid is not a strong reducing agent.
• H₃PO₄ (Phosphoric acid): This acid is not a strong reducing agent.

H₃PO₂ (Hypophosphorous acid) has the strongest reducing ability because it contains the highest number of P-H bonds. These P-H bonds can easily donate electrons, making it a good reducing agent. This characteristic allows it to reduce AgNO₃ to metallic silver.

Therefore, the oxoacid of phosphorus that can reduce AgNO₃ to metallic silver is H₃PO₂.

The correct answer is Option 1: H₃PO₂.

Answer 2

Hypophosphorous Acid as a Reducing Agent 

Hypophosphorous acid (H₃PO₂) is a strong reducing agent that can effectively reduce Ag⁺ ions to Ag, while itself getting oxidized to phosphoric acid (H₃PO₃) as shown in the following reaction:

\[ 3 \, \text{AgNO}_3 + 4 \, \text{H}_3\text{PO}_2 + \text{H}_2\text{O} \rightarrow 3 \, \text{Ag} + 4 \, \text{H}_3\text{PO}_3 + 3 \, \text{HNO}_3 \]

In this reaction, Hypophosphorous acid reduces silver nitrate (AgNO₃) to metallic silver (Ag), while being oxidized to phosphoric acid (H₃PO₃). The nitric acid (HNO₃) is a byproduct of the reaction.