Question

What is the solubility of La(IO₃)₃ in a solution that contains 0.100 M IO₃⁻ ions? (Ksp of La(IO₃)₃ is 7.5 × 10⁻¹²)

Answer 1

Solution and Explanation:

[La3+] = 0.1 M

At the equilibrium:

La(IO3)3 <---->     La3+     +         3 IO3-  

                    0.1 +s             3s      

$\mathrm{Ksp}=[\mathrm{La} 3+][\mathrm{IO} 3-]^{\wedge} 3$

$7.5 * 10^{\wedge}-12=(0.1+s) *(3 s)^{\wedge} 3$

Since Ksp is small, s can be ignored as compared to the 0.1

The above shown expression thus becomes:

$7.5 * 10 \wedge-12=(0.1) *(3 s) \wedge 3$

$7.5 * 10^{\wedge}-12=0.1 * 27(\mathrm{s})^{\wedge} 3$

$s=1.406 * 10^{\wedge}-4 \mathrm{M}$

Answer: 1.4*10^-4 M