Question

X, Y are oxoacids of phosphorous. The number of P – OH bonds in X, Y respectively is:

• A. 1, 4
• B. 4, 1
• C. 2, 4
• D. 1, 1

Hint:

Phosphorous acid (\( H_3PO_3 \)) has two P–OH bonds, whereas Phosphoric acid (\( H_3PO_4 \)) has four P–OH bonds.

Answer 1

The Correct Option is C

Step 1: Identifying X and Y 
- Given reactions: \[ P_2O_3 + H_2O \rightarrow X \] \[ Red \, P_4 + Alkali \rightarrow Y \] - The compounds formed are: 
- \( X \) is Phosphorous acid (\(H_3PO_3\)) 
- \( Y \) is Hypophosphorous acid (\(H_3PO_2\))

Step 2: Identifying P–OH bonds in each acid - The structure of Phosphorous acid (\( H_3PO_3 \)) contains two P–OH bonds. 
- The structure of Hypophosphorous acid (\( H_3PO_2 \)) contains one P–OH bond.

Step 3: Correcting the order 
- The given reactions indicate that \( X = H_3PO_3 \) and \( Y = H_3PO_4 \) (Phosphoric acid).
- Phosphoric acid (\( H_3PO_4 \)) has four P–OH bonds.
- Thus, the number of P–OH bonds in \( X, Y \) are \(2, 4\).

Final Answer: (2,4)

Answer 2

We are given two chemical reactions involving phosphorus compounds and are asked to find the number of P–OH bonds in the resulting oxoacids X and Y.

1. Reaction 1: P₂O₃ + H₂O → X
2. Reaction 2: Red P₄ + alkali → Y

Let us analyze both reactions one by one.

1. Formation of X:
P₂O₃ is also known as diphosphorus trioxide or phosphorus(III) oxide. When it reacts with water, it forms phosphorous acid (H₃PO₃).
The structure of H₃PO₃ can be written as:
O=P(OH)₂ with one additional P–H bond.
So, the structure contains:
- One P=O bond
- One P–H bond
- Two P–OH bonds

Only the P–OH bonds are responsible for the acidic nature of the molecule and can donate protons. The P–H bond is not ionizable in aqueous solution.
Therefore, the number of P–OH bonds in X (phosphorous acid) is 2.

2. Formation of Y:
When red phosphorus reacts with an alkali like NaOH or KOH, it forms hypophosphoric acid, which has the formula H₄P₂O₆.
This acid consists of two phosphorus atoms joined by a P–P bond. Each phosphorus atom in the molecule has two hydroxyl (–OH) groups attached.
Thus, the total number of P–OH bonds in hypophosphoric acid is:
2 (from one phosphorus) + 2 (from the other phosphorus) = 4

Therefore:
- X is phosphorous acid with 2 P–OH bonds
- Y is hypophosphoric acid with 4 P–OH bonds

Final answer:
Number of P–OH bonds in X and Y respectively is: 2, 4