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

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Answer 1 · 2017-05-27T06:21:47

$"Option 2 is correct.........."$

We interrogate the solubility equilibrium:

$Ni(OH)_2(s) rightleftharpoonsNi^(2+) + 2HO^-$

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

$K_"eq"="concentration of products"/"concentration of reactants"$

Of course, there is a catch. The reactant, $Ni(OH)_2(s)$ , as a solid CANNOT express a concentration, and cannot appear in the expression..........

And so $K_"eq"="[Ni^(2+)][HO^-]^2$ (note the exponent on the hydroxide term). Nickel hydroxide would thus be LESS soluble in a basic solution.

Which option expresses the solubility equilibrium that operates for Ni(OH)_2Ni(OH)_2? 1.1. K_"sp"=[Ni^(2+)][HO^-]K_"sp"=[Ni^(2+)][HO^-] 2.2. K_"sp"=[Ni^(2+)][HO^-]^2K_"sp"=[Ni^(2+)][HO^-]^2 3.3. K_"sp"=[Ni^(2+)]xx2[HO^-]K_"sp"=[Ni^(2+)]xx2[HO^-] 4.4. K_"sp"=[Ni^(2+)]^2[HO^-]K_"sp"=[Ni^(2+)]^2[HO^-]