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

The Correct Option is A

Solubility Calculations 

For MY (where MY is a salt):

\(K_{SP} = S^{2}\)

\(S = \sqrt{K_{SP}}\)

\(S = \sqrt{6.2 \times 10^{-13}}\)

\(S = \sqrt{62 \times 10^{-14}}\)

\(S \approx 8 \times 10^{-7}\)

For \({NY_3}\):

\(K_{SP} = 27S^{4}\)

\({NY_3 \rightleftharpoons N^{+3} + 3Y^{-}}\)

\(S = \left( \frac{6.2 \times 10^{-13}}{27} \right)^{1/4} = \left( 0.2296 \times 10^{-13} \right)^{1/4}\)

\(S = 3.89 \times 10^{-4}\)