Question

Upto what ph must a solution containing a precipitate of cr(oh)3 be adjusted so that all of precipitate dissolves when cr3+ = 0.1 mol/l ksp= 6*10^-31

Answer 1

pH should be up to 4.0.

Explanation:

Given : Cr3+ = 0.1 mol/l ksp = 6*10^-31

Find: Upto what ph must a solution containing a precipitate of cr(oh)3 be adjusted so that all of precipitate dissolves.

Solution:

K(sp) = [Cr2+] [OH-]^3

 [OH]^-3 = K(sp)  Cr3+ = 6 * 10^-31 / 1*10 = 6 * 10^-30

 [OH-] = 1.8 * 10^-10

 p(OH) = log1.8 + log10^10

   = 10 + 0.25 + 1

   = 11.25

p(H) = 14 - 11.25 = 2.75

So the answer is the pH should be up to 4.0.