Question

4 mL of 'X volume' \( \text{H}_2\text{O}_2 \) on heating gives 80 mL of oxygen at STP. The value of X is

• A. 10
• B. 20
• C. 15
• D. 40

Hint:

- The "volume strength" of an \( \text{H}_2\text{O}_2 \) solution (e.g., 'X volume') refers to the volume of \( \text{O}_2 \) gas (at STP) liberated from one unit volume of the \( \text{H}_2\text{O}_2 \) solution upon complete decomposition. - For example, '10 volume' \( \text{H}_2\text{O}_2 \) means 1 mL of this solution will produce 10 mL of \( \text{O}_2 \) at STP. - Decomposition: \( 2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2 \).

Answer 1

The Correct Option is B

'X volume' of \( \text{H}_2\text{O}_2 \) means that 1 volume (e.
g.
, 1 mL or 1 L) of the \( \text{H}_2\text{O}_2 \) solution gives X volumes (X mL or X L) of oxygen gas (\( \text{O}_2 \)) at STP upon decomposition.
The decomposition reaction is: \( 2\text{H}_2\text{O}_2 \text{(aq)} \longrightarrow 2\text{H}_2\text{O(l)} + \text{O}_2\text{(g)} \).
Given: 4 mL of 'X volume' \( \text{H}_2\text{O}_2 \) solution gives 80 mL of \( \text{O}_2 \) at STP.
According to the definition of 'X volume': 1 mL of \( \text{H}_2\text{O}_2 \) solution gives X mL of \( \text{O}_2 \) at STP.
So, 4 mL of \( \text{H}_2\text{O}_2 \) solution gives \( 4 \times X \) mL of \( \text{O}_2 \) at STP.
We are given that this volume of oxygen is 80 mL.
Therefore, \[ 4X = 80 \] \[ X = \frac{80}{4} = 20 \] So, the value of X is 20.
The solution is '20 volume' \( \text{H}_2\text{O}_2 \).
This matches option (2).