JEE Main 2023 · 30 January · evening · Numerical answer · +4 / −0
The strength of 50 volume solution of hydrogen peroxide is ______ g / L (Nearest integer).
Given:
Molar mass of H₂ O₂ is 34 g mol⁻¹
Molar volume of gas at STP=22.7 L
Answer and solution
Answer 150
Solution
Chemistry ma’am · 4 steps
Volume strength tells you how much oxygen comes out. Work back to the peroxide through the 2 : 1 ratio.
- What 50 volume means. 1 L of this solution releases 50 L of O₂ at STP when it decomposes. So find how much H₂O₂ is needed to give 50 L of oxygen.
2H₂O₂ → 2H₂O + O₂
- Moles of oxygen. n(O₂) = 50/22.7 = 2.203 mol. The equation shows 2 mol of H₂O₂ give 1 mol of O₂, so n(H₂O₂) = 2 × 2.203 = 4.405 mol in 1 L.
- Convert to grams. Mass in 1 L = 4.405 × 34 = 149.8 g. In one line: (68 × 50)/22.7 = 149.8 g L⁻¹.
- So. The strength is 149.8 g L⁻¹, which rounds to 150.
The common slip: 152. Using the memorised 22.4 L instead of the given 22.7 L gives (68 × 50)/22.4 = 151.8, which rounds to 152, not 150.
The idea to keep. Volume strength is litres of O₂ per litre of solution. Divide by the molar volume, double it for H₂O₂, then multiply by 34. Always use the molar volume the question gives you.
Answer from the NTA final answer key. Solution by PrepWiser.