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.