Question

Ignoring activities, determine the molar solubility of copper(I) azide (CuN3) in a solution with a pH of 11.35. The Ksp for CuN3 is 4.9 × 10–9. The Ka for HN3 is 2.2 × 10–5.

Answer 1

pH = 11.35

[H+] = 10^-11.35 = 4.47 x 10^-12 M

HN3 (aq) ----------------> H+ (aq)   +   N3- (aq)

[H+] = [N3-] = 4.47 x 10^-12 M

CuN3 (s)   ---------------> Cu+    +   N3-

                                        S          4.47 x 10^-12 + S

Ksp = [Cu+][N3-]

4.9 × 10^–9 = S x (4.47 x 10^-12 + S )

4.9 × 10^–9 = 4.47 x 10^-12 S + S^2

S = 7.00 x 10^-5

solubility = 7.00 x 10^-5 M