What is the solubility of La(IO₃)₃ in a solution that contains 0.400 M IO₃⁻ ions? (Ksp of La(IO₃)₃ is 7.5 × 10⁻¹²)

Question

I got 8.85 × 10⁻⁵ M but it said that was wrong not sure what I did wrong

Answer 1

This is a common ion problem.

La(IO₃)₃(s) <==> La³⁺(aq) + 3IO₃^-(aq) ... Ksp = 7.5x10^-12

Write the Ksp expression:

Ksp = [La³⁺] [IO₃^-]³

Substitute and solve for [La3+]

7.5x10^-12 = [La³⁺][0.400]³

[La³⁺] = 1.17x10^-10 M = solubility of La(IO₃)₃ in 0.400 M IO₃^-