AP Chemistry 7.11 A Calculate the Solubility of a Salt Based on the Value of Ksp for the Salt Questions

Practice AP Chemistry questions on writing Ksp expressions and calculating molar solubility, ion concentrations, or dissolved mass for saturated salts.

Exam points

Explain how reaction rates depend on concentration, collisions, activation energy and reaction pathways.
Apply rate laws and experimental data to determine reaction order, constants and mechanisms.

[Maximum number: 2]

Strontium hydroxide dissolves in water according to the following equation. The $K_{s p}$ expression for strontium hydroxide is provided.

\mathrm{Sr}(\mathrm{OH})_{2}(s) \rightleftarrows \mathrm{Sr}^{2+}(a q)+2 \mathrm{OH}^{-}(a q) \quad K_{s p}=\left[\mathrm{Sr}^{2+}\right]\left[\mathrm{OH}^{-}\right]^{2}

Figure for Question AP Chemistry 7.11 A Calculate the Solubility of a Salt Based on the Value of Ksp for the Salt Questions question 1 — AP Chemistry

(a)

The student prepares a saturated solution by adding excess $\mathrm{Sr}(\mathrm{OH})_{2}(s)$ to distilled water and stirring until no more solid dissolves. The student then determines that $\left[\mathrm{Sr}^{2+}\right]=0.043 M$ in the solution.

[ 2 ]

(i) For the correct calculated value: 1 point

\frac{0.043 \mathrm{~mol} \mathrm{Sr}^{2+}}{1 \mathrm{~L}} \times \frac{2 \mathrm{~mol} \mathrm{OH}^{-}}{1 \mathrm{~mol} \mathrm{Sr}^{2+}}=0.086 M \mathrm{OH}^{-}

(i)

Calculate the value of $\left[\mathrm{OH}^{-}\right]$ in the solution.

[ 1 ]

(i) For the correct calculated value: 1 point

\frac{0.043 \mathrm{~mol} \mathrm{Sr}^{2+}}{1 \mathrm{~L}} \times \frac{2 \mathrm{~mol} \mathrm{OH}^{-}}{1 \mathrm{~mol} \mathrm{Sr}^{2+}}=0.086 M \mathrm{OH}^{-}

(ii)

Calculate the value of $K_{s p}$ for $\mathrm{Sr}(\mathrm{OH})_{2}$ .

[ 1 ]

For the correct calculated value, consistent with (b)(i): 1 point

K_{s p}=\left[\mathrm{Sr}^{2+}\right]\left[\mathrm{OH}^{-}\right]^{2}=(0.043)(0.086)^{2}=3.2 \times 10^{-4}

Total for part (b) 2 points

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AP Chemistry 7.11 A Calculate the Solubility of a Salt Based on the Value of Ksp for the Salt Questions question 1

Question (a)

Question (i)

Question (ii)