Chapter 17.3, Problem 26PP

Interpretation Introduction

Interpretation:

Whether the precipitate will form or not needs to be determined.

Concept introduction:

When the Q_sp of a solution becomes greater than the K_sp a precipitate will form.

Answer to Problem 26PP

A precipitate will form.

Explanation of Solution

$\text{Concentration of Mg in solution}=\frac{0.20\times 250}{1000}=0.05M$ ’

${\text{Concentration of OH}}^{\text{-}}\text{ in solution}=\frac{0.0025\times 750}{1000}=0.001875M$ ’

$\begin{array}{l}{Q}_{sp}=[M{g}^{2+}]{[}^O\\ Q_{sp}=0.05\times {0.001875}^2\\ Q_{sp}=1.76\times {10}^{-7}\end{array}$

Which is greater than the K_sp so precipitate will form.

Conclusion

A precipitate of magnesium hydroxide will form.