CAIE IGCSE Chemistry Diffusion Question Bank

Practise explaining diffusion through random particle motion and predict relative gas diffusion rates from temperature and relative molecular mass.

Syllabus
2026–2028
Topic
1.2
Level
—

Exam points

  • describe particles spreading randomly from higher to lower concentration until evenly distributed
  • predict faster diffusion at higher temperature because particles have more kinetic energy and move faster
  • calculate or compare relative molecular masses and identify the lighter gas as diffusing faster

Covered syllabus points

1.2.1—Diffusion using kinetic particle1.2.2—Effect of relative molecular mass on

1.2 Diffusion question 1

[Maximum number: 7]

Concentrated ammonia solution gives off ammonia gas. Concentrated hydrochloric acid gives off hydrogen chloride gas. Ammonia, NH3\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 Diffusion question 1 — CAIE IGCSE Chemistry

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

Question (a)

(a)

Name the process by which the ammonia and hydrogen chloride gases move in the tube.

[ 1 ]

Question (b)

(b)

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

[ 3 ]

Question (c)

(c)

The experiment was repeated at a higher temperature.

Predict how the results of the experiment would be different. Explain your answer.

[ 3 ]
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