Question

$MY$ and $N{Y}_3$, 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 regards to $MY$ and $N{Y}_3$?

• A. The molar solubilities of $MY$ and $N{Y}_3$ in water are identical.
• B. The molar solubility of $MY$ in water is less than that of $N{Y}_3$.
• C. The salts $MY$ and $N{Y}_3$ are more soluble in $0.5MKY$ than in pure water.
• D. The addition of the salt of KY to solution of $MY$ and $N{Y}_3$ will have no effect on their solubilities.

Answer 1

Answer: (B)

The molar solubility of $MY$ in water is less than that of $N{Y}_3$.

The statement (B) is true.
The molar solubility of $MY$ in water is less than that of $N{Y}_3$

$MY\to M^{+}+Y^{-}$

$N{Y}_3\to N^{3+}+3Y^{-}$

For MY, the molar solubility $=\sqrt{Ksp}=\sqrt{6.2\times {10}^{-13}}=7.88\times {10}^{-7}M$

For $N{Y}_3$, the molar solubility $=(\frac{Ksp}{27}{)}^{\left(1/4\right)}=(\frac{6.2\times {10}^{-13}}{27}{)}^{\left(1/4\right)}=3.9\times {10}^{-4}M$