Q38 · Practice questionSimple familiar4 marks
QUESTION 38 (4 marks)
A saturated solution is in contact with excess . Some sodium hydroxide is added, with negligible volume change.
a) Use an equation to explain the change in dissolved magnesium-ion concentration. [3 marks]
b) State whether the solubility product changes at constant temperature. [1 marks]
WORKED SOLUTION
4 marksPractice marking scheme
a) Magnesium-ion concentration decreases as magnesium hydroxide precipitates. b) Ksp is unchanged.
. Added hydroxide favours the reverse reaction. Dissolved magnesium is removed into solid while the product of ion concentrations returns to Ksp.
- Writes correct equilibrium equation. [1 marks]
- Identifies added OH⁻ as a common ion and reverse shift. [1 marks]
- Explains decreased dissolved Mg²⁺/increased precipitate. [1 marks]
- States Ksp remains constant at constant temperature. [1 marks]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusHow many marks did you earn?
Compare your working with the guide above.