# Which option expresses the solubility equilibrium that operates for Ni(OH)_2? 1. K_"sp"=[Ni^(2+)][HO^-] 2. K_"sp"=[Ni^(2+)][HO^-]^2 3. K_"sp"=[Ni^(2+)]xx2[HO^-] 4. K_"sp"=[Ni^(2+)]^2[HO^-]

May 27, 2017

$\text{Option 2 is correct..........}$

#### Explanation:

We interrogate the solubility equilibrium:

$N i {\left(O H\right)}_{2} \left(s\right) r i g h t \le f t h a r p \infty n s N {i}^{2 +} + 2 H {O}^{-}$

This is clearly an equilibrium reaction, and as with any equilibrium we write the equilibrium constant,

${K}_{\text{eq"="concentration of products"/"concentration of reactants}}$

Of course, there is a catch. The reactant, $N i {\left(O H\right)}_{2} \left(s\right)$, as a solid CANNOT express a concentration, and cannot appear in the expression..........

And so ${K}_{\text{eq"=}} \left[N {i}^{2 +}\right] {\left[H {O}^{-}\right]}^{2}$ (note the exponent on the hydroxide term). Nickel hydroxide would thus be LESS soluble in a basic solution.