Question

$C{a}_3\left(P{O}_4{)}_2\right(s)\rightleftharpoons 3C{a}^{2+}(aq)+2P{O}_4^{3-}(aq)$
What is the equilibrium expression for the dissolution of $C{a}_3(P{O}_4{)}_2$ where the above is true?

• A. $K_{sp}=\left[C{a}^{2+}{]}^3\right[{P{O}_4}^{3-}{]}^2$
• B. $K_{sp}=\left[C{a}^{2+}{]}^2\right[{P{O}_4}^{3-}{]}^3$
• C. $K_{sp}=\left[C{a}^{2+}\right]\left[{P{O}_4}^{3-}\right]/\left[C{a}_3\right(P{O}_4{)}_2]$
• D. $K_{sp}=\left[C{a}^{2+}{]}^3\right[{P{O}_4}^{3-}{]}^2/\left[C{a}_3\right(P{O}_4{)}_2]$

Answer 1

The correct option is A $K_{sp}=\left[C{a}^{2+}{]}^3\right[{P{O}_4}^{3-}{]}^2$

$C{a}_3\left(P{O}_4{)}_2\right(s)\leftrightharpoons 3C{a}^{2+}(aq)+2P{O}_4^{3-}(aq)$

$K_{sp}=\frac{\left[C{a}^{2+}{]}^3\right[P{O}_4^{3-}{]}^2}{\left[C{a}_3\right(P{O}_4{)}_2]}$

Since, $C{a}_3(P{O}_3{)}_2$ is solid, its concentration is taken to be $1$.

Hence, $K_{sp}=\left[C{a}^{2+}{]}^3\right[P{O}_4^{3-}{]}^2$