# The solubility of an ionic compound, MX (molar mass of 346g) is 4.63*10^-3 g/L. What is Ksp for the compound?

Jun 20, 2016

${K}_{s p} \cong 1.8 \times {10}^{-} 10$

#### Explanation:

$M X \left(s\right) r i g h t \le f t h a r p \infty n s {M}^{+} + {X}^{-}$

This is an equilibrium reaction, and as usual we write the equilibrium expression:

${K}_{s p} = \left[{M}^{+}\right] \left[{X}^{-}\right]$

$\left[M X\right]$ does not appear in the expression inasmuch as we cannot speak of the concentration of a solid.

Now $S$ $=$ $4.63 \times {10}^{- 3} \cdot g \cdot {L}^{-} 1$.

$=$ $\frac{4.63 \times {10}^{- 3} \cdot g}{346 \cdot g \cdot m o l \cdot {L}^{-} 1}$ $=$ $1.34 \times {10}^{-} 5 \cdot m o l \cdot {L}^{-} 1$ with respect to $M X$.

Since $\left[M X\right]$ $=$ $\left[{M}^{+}\right]$ $=$ $\left[{X}^{-}\right]$,

${K}_{s p} = \left[{M}^{+}\right] \left[{X}^{-}\right]$ $=$ ${\left(1.34 \times {10}^{-} 5\right)}^{2}$