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CAIE A-Level Chemistry 25.1.10 Common-Ion Effect and Solubility

Practise explaining and calculating reduced solubility when a solution already contains one dissolution ion.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • identify the ion shared by the added electrolyte and the sparingly soluble solid’s equilibrium
  • use Le Chatelier’s principle to explain a shift towards solid and lower molar solubility
  • include the pre-existing common-ion concentration in Ksp and solve only for the additional dissolved amount

25.1.10—Common ion effect and solubility question 1

[Maximum number: 2]

Calcium iodate (V),Ca(IO3)2(\mathrm{V}), \mathrm{Ca}\left(\mathrm{IO}_{3}\right)_{2}, is sparingly soluble in water.

The concentration of its saturated solution is 5.6×10−3 moldm−35.6 \times 10^{-3} \mathrm{~mol} \mathrm{dm}^{-3} at 298 K .

When a few cm3\mathrm{cm}^{3} of concentrated Ca(NO3)2(aq)\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) is added to a saturated solution of Ca(IO3)2\mathrm{Ca}\left(\mathrm{IO}_{3}\right)_{2} a white precipitate forms.

Identify the white precipitate and give an explanation for this observation.

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