Question

Which of the saturated solutions below would have the highest [OH- ]? a. M(OH)2 Ksp = 4.25 x 10-6 b. M(OH)2 Ksp = 7.39 x 10-4 c. M(OH)2 Ksp = 2.64 x 10-3 d. M(OH)2 Ksp = 8.52 x 10-8

Answer 1

M(OH)2 Ksp = 2.64 x 10-3

Step-by-step explanation:

Recall that for M(OH)2, its dissolution in water gives;

M(OH)2(s) ----> M^2+(aq) + 2OH^-(aq)

Ksp= x × (2x)^2

Ksp= 4x^3

a)

Ksp= 4.25 x 10^-6

Ksp= 4x^3

x= 3√Ksp/4

x= 3√4.25 x 10^-6/4

x= 1.02 ×10^-2 moldm-3

For 2 OH^- = 2 × 1.02 ×10^-2 moldm-3 = 2.04 ×10^-2 moldm-3

b)

Ksp= 7.39 x 10^-4

Ksp= 4x^3

x= 3√Ksp/4

x= 3√7.39 x 10^-4/4

x= 5.7 ×10^-2 moldm-3

For 2 OH^- = 2 × 5.7 ×10^-2 moldm-3= 11.4 ×10^-2 moldm-3

c)

Ksp= 2.64 x 10^-3

Ksp= 4x^3

x= 3√Ksp/4

x= 3√2.64 x 10^-3/4

x= 8.7 ×10^-2 moldm-3

For 2 OH^- = 2 × 8.7 ×10^-2 moldm-3 = 17.4 ×10^-2 moldm-3

d)

Ksp= 8.52 x 10^-8

Ksp= 4x^3

x= 3√Ksp/4

x= 3√8.52 x 10^-8/4

x= 2.77 ×10^-3 moldm-3

For 2 OH^- = 2 × 2.77 ×10^-3 moldm-3 = 5.54 ×10^-3 moldm-3

Hence, M(OH)2 Ksp = 2.64 x 10-3 has the highest [OH- ].