JEE Main 2020 · 3 September · evening · Single correct · +4 / −1
The strengths of 5.6 volume hydrogen peroxide (of density 1 g/mL) in terms of mass percentage and molarity (M), respectively, are: (Take molar mass of hydrogen peroxide as 34 g/mol)
- (a) 0.85 and 0.5
- (b) 0.85 and 0.25
- (c) 1.7 and 0.25
- (d) 1.7 and 0.5
Answer and solution
Answer (d) 1.7 and 0.5
Solution
Chemistry ma’am · 4 steps
Read 5.6 volume as 5.6 L of oxygen from 1 L of solution, then work back to the peroxide.
- Meaning of volume. 5.6 volume H₂O₂ means 1 L of the solution releases 5.6 L of O₂ at STP when it decomposes. At STP, 1 mol of gas occupies 22.4 L, so this is 5.6/22.4 = 0.25 mol of O₂.
2H₂O₂ → 2H₂O + O₂
- Moles of peroxide. 2 mol of H₂O₂ give 1 mol of O₂. So 0.25 mol of O₂ comes from 2 × 0.25 = 0.5 mol of H₂O₂, all in 1 L. The molarity is 0.5 M.
- Mass percentage. Mass of H₂O₂ is 0.5 × 34 = 17 g. With density 1 g mL⁻¹, 1 L of solution weighs 1000 g. So the mass percentage is 17/1000 × 100 = 1.7.
- So. The strengths are 1.7 (mass percentage) and 0.5 M, which is option (d).
The idea to keep. Volume strength of H₂O₂ is 11.2 × molarity, because 2 mol of peroxide give 1 mol of O₂. Never forget that 2 : 1 ratio.
Answer from the NTA final answer key. Solution by PrepWiser.