AP Chemistry Unit 8.11: pH and Salt Solubility

Practice AP Chemistry Unit 8.11 questions on predicting pH effects on salt solubility using Ksp equilibria and Le Châtelier reasoning.

Covered syllabus points

8.11.A—Identify the qualitative effect of changes in pH on the solubility of a salt

[Maximum number: 1]

Answer the following questions about magnesium.

In a separate experiment, the student adds $\mathrm{HNO}_{3}(a q)$ to decrease the pH of a saturated

solution containing undissolved $\mathrm{Mg}(\mathrm{OH})_{2}(s)$ . Does the amount of undissolved $\mathrm{Mg}(\mathrm{OH})_{2}(s)$

increase, decrease, or remain the same as the $\mathrm{HNO}_{3}(a q)$ is added? Justify your answer.

F For the correct answer and justification:

Point 10

Decrease. The $\mathrm{H}^{+}$ from $\mathrm{HNO}_{3}(a q)$ will react with $\mathrm{OH}^{-}$ , decreasing [ $\mathrm{OH}^{-}$ ] and

causing $Q<K_{s p}$ . As a result, more $\operatorname{Mg}(\mathrm{OH})_{2}(s)$ will dissolve until equilibrium is

reestablished, resulting in less $\mathrm{Mg}(\mathrm{OH})_{2}(s)$ .

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Covered syllabus points

8.11 pH and Solubility question 1