The ksp of al (oh) 3 is 2 x 10-32. at what ph will a 0.4 m al3 + solution begin to show precipitation of al (oh) 3?

At pH = 6.19, solution begin to show precipitation

Explanation:

Ksp of Al (OH) ₃ is:

Al (OH) ₃ (s) ⇄ Al³⁺ (aq) + 3 OH⁻ (aq)

At equilibrium:

Ksp = 2x10⁻³² = [Al³⁺] [OH⁻]³

0.4M Al (OH) ₃ produce:

[Al³⁺] = X

[OH⁻] = 3X

Replacing:

2x10⁻³² = [X] [3X]³

2x10⁻³² = 27X⁴

7.41x10⁻³³ = X⁴

5.217x10⁻⁹ = X

Thus:

[OH⁻] = 3X = 3*5.217x10⁻⁹

[OH⁻] = 1.565x10⁻⁸M

pOH = - log [OH⁻] = 7.805

pH = 14 - pOH

pH = 6.19

Thus, at pH = 6.19, solution begin to show precipitation.