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CAIE IGCSE Chemistry Molecular Mass and Gas Diffusion

CAIE IGCSE Chemistry Molecular Mass and Gas Diffusion
Cambridge IGCSE Chemistry 0620 syllabus for exams in 2026, 2027 and 20282026–2028

Practise calculating relative molecular mass to rank gas diffusion rates and predict where reacting gases meet or which indicator changes first.

How this is tested

  • calculate M_r from each gas formula and identify the lower-M_r gas as diffusing faster
  • predict a reaction ring nearer the heavier, slower gas because the lighter gas travels further
  • use indicator-change time or distance travelled to compare diffusion rates under equal conditions

Question 1

[Maximum number: 1]

Which gas has the slowest rate of diffusion?

A

H2\mathrm{H}_{2}

B

NH3\mathrm{NH}_{3}

C

CH4\mathrm{CH}_{4}

D

CO2\mathrm{CO}_{2}