Question

$MY$ and $NY_3$, two nearly insoluble salts, have the same $K_{SP}$ values of $6.2 \times 10^{-13}$ at room temperature. Which statement would be true in regard to $MY$ and $NY_3$ ?

• A. The molar solubility of MY in water is less than that of $NY_3$
• B. The salts $MY$ and $NY_3$ are more soluble in 0.5 M KY than in pure water
• C. The addition of the salt of KY to solution of $MY$ and $NY_3$ will have no effect on their solubilities
• D. The molar solubilities of $MY$ and $NY_3$ in water are identical

Answer 1

Answer: (A)

The molar solubility of MY in water is less than that of $NY_3$

Answer 2

For MY $K_{SP} = S^{2}$ $S= \sqrt{K_{SP}}$ $= \sqrt{6.2 \times10^{-13}}$ $= \sqrt{62 \times10^{-14}}$ $\approx8 \times10^{-7}$ for ${NY_3}$, $K_{SP} = 27S^{4}$ {NY_3 <=>\underset{\text{ S}}{ { N^{+3} }}$+$\underset{\text{ 3S}}{ { 3Y^{-}}} } $S = \left( \frac{6.2 \times 10^{-13}}{27}\right)^{1/4} = \left(0.2296 \times 10^{-13}\right)^{1/4}$ $S = 3.89 \times10^{-4}$