FRQ — Equilibrium

Case study·Hard exam skill (4/5)·Calculator allowed

Difficulty guide

The label describes the problem, not your ability.

1/5 - Foundational

Warm-up setup; checks one basic idea.

2/5 - Routine exam skill

Normal syllabus skill; usually one main rule or interpretation.

3/5 - Standard multi-step

Exam-style problem with multiple steps or a common trap.

4/5 - Hard exam skill

High-end exam problem; combines methods carefully.

5/5 - Challenge

Stretch problem beyond normal exam pressure.

Question

A lab tests precipitation of

\mathrm{Mg(OH)_2}

with

K_{sp}=1.0\times10^{-11}

. Three solutions have

[\mathrm{Mg^{2+}}]=1.0\times10^{-3}\,\mathrm{M}

and hydroxide concentrations

1.0\times10^{-5}\,\mathrm{M}

1.0\times10^{-4}\,\mathrm{M}

and

1.0\times10^{-3}\,\mathrm{M}

respectively.

Total: 5 marks

(a) Find $Q_{sp}$ for the first solution. (1 mark)

(b) Find $Q_{sp}$ for the second solution. (1 mark)

(d) State in which solutio $n(s) precipitation begins$ . (2 marks)

Your response (optional — you can also work on paper)

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