Question

The magnesium and calcium ions present in seawater ([Mg2+] = 0.059 M and [Ca2+] = 0.011 M) can be separated by selective precipitation with KOH.

If the concentration of Mg2+ in the solution were 0.039 M, what minimum [OH−] triggers precipitation of the Mg2+ ion? (Ksp=2.06×10−13.)

Answer 1

the minimum [OH−] triggers precipitation = 2.3x10^-6 M

Step-by-step explanation:

Mg2+ + 2OH- --> Mg(OH)2(s)

Ksp = [Mg2+][OH-]^2

(2.06x10^-13) = (0.039*x^2)

x = [OH-] = 2.3*10^-6 M

the minimum [OH−] triggers precipitation = 2.3x10^-6 M