CAIE IGCSE Chemistry Molecular Mass and Gas Diffusion

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

Exam points

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

[Maximum number: 3]

Concentrated ammonia solution gives off ammonia gas. Concentrated hydrochloric acid gives off hydrogen chloride gas. Ammonia, $\mathrm{NH}_{3}$ , and hydrogen chloride, HCl , are both colourless gases. Ammonia reacts with hydrogen chloride to make the white solid ammonium chloride.

Apparatus is set up as shown.

Figure for Question 1.2.2—Effect of relative molecular mass on question 1 — CAIE IGCSE Chemistry

After ten minutes a white solid forms in the tube where the gases meet.

At which point, A, B, C or D, does the white solid form? Explain why the white solid forms at that point.
the solid forms at
explanation

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1.2.2—Effect of relative molecular mass on question 1