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CAIE IGCSE Chemistry Aqueous Cation Tests

Practise identifying aqueous cations from precipitate colours, solubility in excess reagent and the ammonia released by an ammonium salt.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • add sodium hydroxide or aqueous ammonia and record the precipitate colour for the named cation
  • use solubility in excess reagent to distinguish ions such as aluminium, zinc and copper
  • identify ammonium ions by warming with sodium hydroxide and testing the released ammonia gas

12.5.2—Cation tests using aqueous sodium question 1

[Maximum number: 3]

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 12.5.2—Cation tests using aqueous sodium question 1 — CAIE IGCSE Chemistry

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

Some of the white solid is removed from the tube and dissolved in water.

Describe how the white solid could be tested to show it contains,

ammonium ions,
test
result

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