Question

What is the solubility of La(IO₃)₃ in a solution that contains 0.100 M La³⁺ ions? (Ksp of La(IO₃)₃ is 7.5x10^-12)

Answer 1

[La3+] = 0.1 M

At equilibrium:
La(IO3)3 <---->     La3+     +         3 IO3-  
                     0.1 +s             3s      
Ksp = [La3+][IO3-]^3
7.5*10^-12=(0.1 + s)*(3s)^3
Since Ksp is small, s can be ignored as compared to 0.1
Above expression thus becomes:
7.5*10^-12=(0.1)*(3s)^3
7.5*10^-12= 0.1 * 27(s)^3
s = 1.406*10^-4 M
Answer: 1.4*10^-4 M