Question

For the following question, enter the correct numerical value up to TWO decimal places. If the numerical value has more than two decimal places, round-off the value to TWO decimal places. (For example: Numerical value 5 will be written as 5.00 and 2.346 will be written as 2.35) 20.4 g of \( \mathrm{H_2O_2} \) solution on decomposition gives 1.68 L of \( \mathrm{O_2} \) at STP. Percentage strength by weight of the solution is _____

Hint:

Use the decomposition reaction of hydrogen peroxide to relate the volume of oxygen evolved to the mass of \( H_2O_2 \).

Answer 1

Correct Answer: 25

Step 1: Calculate moles of oxygen liberated at STP: \[ \text{Moles of } O_2 = \frac{1.68}{22.4} = 0.075 \,\text{mol} \]
Step 2: Decomposition reaction: \[ 2H_2O_2 \rightarrow 2H_2O + O_2 \] From the equation, 1 mol of \( O_2 \) is produced from 2 mol of \( H_2O_2 \). \[ \text{Moles of } H_2O_2 = 2 \times 0.075 = 0.15 \,\text{mol} \]
Step 3: Mass of \( H_2O_2 \): \[ \text{Mass} = 0.15 \times 34 = 5.10 \,\text{g} \]
Step 4: Percentage strength by weight: \[ %\text{ by weight} = \frac{5.10}{20.4} \times 100 = 25.00 \] Hence, the percentage strength of the solution is \[ \boxed{25.00} \]