Question

What is the Nickel ion consentration in a 2.5x10^-5 M solution of Ni(IO₃)₂ ? k_sp=4.71x10^-5

(answer is not 2.28x10^-2 M, please explain)

Answer 1

Nickel Iodate dissociates in aqueous solution according to the followoing equation

       Ni(IO₃)₂ (s) = Ni²⁺ (aq) + 2 IO₃^- (aq)

The K_sp of Ni(IO₃)₂ is 4.71x10^-5 .

So, maximum solubility of Ni(IO₃)₂ is

        

(This is where you have arrived and this is the maximum permissible concentration)

But the concentration of Ni(IO₃)₂ is 2.5 x 10^-5 M.

Assuming complete dissociation the concentration of Ni²⁺ is 2.5 x 10^-5 M.