91Ó°ÊÓ

The Qsp-ion-product expression is obtained by multiplying the concentrations of ions generated by the dissolution of a chemical. When a solution is saturated, the Qsp value is referred to as the Ksp value (solubility-product constant).

${\mathbf{\text{MX}}}_{\mathbf{\text{2}}}{\mathbf{\text{> >M}}}^{\mathbf{\text{2 +}}}{\mathbf{\text{+ 2X}}}^{\mathbf{\text{-}}}$

We do not include the solid and liquid states in the equations

role="math" localid="1663285791272" $\mathbf{\text{Ksp =}}\left[{\text{M}}^{\text{2 +}}\right]{\left[{\text{X}}^{\text{-}}\right]}^{\mathbf{\text{2}}}$

a.) Let us obtain the ion-product expression for calcium chromate

Calcium chromate's formula is ${\text{CaCrO}}_{\text{4}}$.

$$\begin{gathered} {\text{CaCrO}}_4\left(s\right)⇔{\text{Ca}}^{2+}\left(aq\right)+{\text{CrO}}_4^{2-}\left(aq\right) \\ \text{Ksp =}\left[{\text{Ca}}^{\text{2 +}}\right]\left[{\text{CrO}}_{\text{4}}^{\text{2 -}}\right] \end{gathered}$$

Therefore, the ion-product expression for calcium chromate is $\left[{\text{Ca}}^{\text{2 +}}\right]\left[{\text{CrO}}_{\text{4}}^{\text{2 -}}\right]$.

b.) Let us obtain the ion-product expression for silver cyanide.

The formula for silver cyanide is $AgCN$.

$$\begin{gathered} AgCN\left(s\right)⇔A{g}^{+}\left(aq\right)+C{N}^{-}\left(aq\right) \\ \text{Ksp =}\left[{\text{Ag}}^{\text{+}}\right]\left[{\text{CN}}^{\text{-}}\right] \end{gathered}$$

Therefore, the ion-product expression for silver cyanide is$\left[{\text{Ag}}^{\text{+}}\right]\left[{\text{CN}}^{\text{-}}\right]$

Let us obtain the ion-product expression for Nickelsulphide.

The formula for silver cyanide is NiS.

$NiS\left(s\right)⇔N{i}^{2+}\left(aq\right)+S^{2-}\left(aq\right)$

role="math" localid="1663287004709" $$\begin{gathered} \left(\text{a}\right)\text{Calcium chromate: Ksp =}\left[{\text{Ca}}^{\text{2 +}}\right]\left[{\text{CrO}}_{\text{4}}^{\text{2 -}}\right] \\ \left(\text{b}\right)\text{Silver cyanide: Ksp =}\left[{\text{Ag}}^{\text{+}}\right]\left[{\text{CN}}^{\text{-}}\right] \\ \left(\text{c}\right)\text{Nickel}\left(\text{II}\right)\text{sulfide: Ksp =}\left[{\text{Ni}}^{\text{2 +}}\right]\left[{\text{S}}^{\text{2 -}}\right] \end{gathered}$$

Therefore, the ion-product expression for silver cyanide is $\left[{\text{Ni}}^{\text{2 +}}\right]\left[{\text{S}}^{\text{2 -}}\right]$.