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AP® Chemistry

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Sea Water

APCHEM-4SIQ1X

Sea water is 0.060 M magnesium ions and 0.010 M calcium ions. The $K_{sp}$ of magnesium hydroxide is $2.1 × 10^{-13}$ and $K_{sp}$ of calcium hydroxide is $4.7 × 10^{-6}$.

What is the concentration of magnesium ions when the concentration of hydroxide is high enough to precipitate out both magnesium and calcium ions?

A

$2.2 × 10^{-11} \ \text{M}$

B

$4.9 × 10^{-10} \ \text{M}$

C

$4.7 × 10^{-6} \ \text{M}$

D

$2.1 × 10^{-2} \ \text{M}$