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2021 O Level Chem P1 Q4 — Diffusion / Kinetic Particle Theory Solution

Diffusion / Kinetic Particle Theory 2021 O Level Pure Chemistry · Paper 1 · Q4

Question

The rate of diffusion of five gases is measured. The gases are CO, CO₂, C₂H₄, C₃H₈ and N₂. The list gives four pairs of gases. 1: CO and C₂H₄. 2: CO and N₂. 3: CO₂ and C₃H₈. 4: C₂H₄ and C₃H₈. In which pairs would both gases diffuse at the same rate, under the same conditions of temperature and pressure?

A1, 2 and 3
B1 and 2 only
C1 only
D3 and 4

Correct answer: A

Video Solution

Explanation

Answer: A (1, 2 and 3). The rate of diffusion of a gas depends on its relative molecular mass: lighter molecules diffuse faster. Two gases diffuse at the same rate, under the same temperature and pressure, only if they have the same relative molecular mass (Mᵣ).

Mᵣ values: CO = 28, C₂H₄ = 28, N₂ = 28, CO₂ = 44, C₃H₈ = 44.

Pair 1 (CO and C₂H₄): 28 = 28 ✓. Pair 2 (CO and N₂): 28 = 28 ✓. Pair 3 (CO₂ and C₃H₈): 44 = 44 ✓. Pair 4 (C₂H₄ and C₃H₈): 28 ≠ 44 ✗. So pairs 1, 2 and 3 diffuse at the same rate.

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