Question

13. a) A generic salt, AB, has a molar mass of 321 g/mol and a solubility of 8.80 g/L at 25 °C. What is the Ksp of this salt at 25 °C?

b) The Ksp of manganese(II) hydroxide, Mn(OH)2, is 2.00 × 10-13. Calculate the molar solubility of this compound.

c) Above what Fe2 concentration will Fe(OH)2 precipitate from a buffer solution that has a pH of 9.73? The Ksp of Fe(OH)2 is 4.87×10-17.

d) What concentration of SO32– is in equilibrium with Ag2SO3(s) and 2.90 × 10-3 M Ag ? The Ksp of Ag2SO3 can be found here.

In a saturated aqueous solution of CaF2, the calcium ion concentration is 0.000215 M and the fluoride ion concentration is 0.000431 M. Calculate the solubility product, Ksp, for CaF2.

e) The Ksp of lanthanum fluoride, LaF3, is 2.00 × 10-19. Calculate the molar solubility of this compound.

f) The Ksp of cadmium carbonate, CdCO3, is 1.0 × 10-12. Calculate the solubility of this compound in g/L.

Answer 1

Q13

a

For solubility comparisson:

AB <-> A+ + B-;

Ksp = [A+][B-]

Ksp = S*S

Ksp = S^2 -->

S = sqrt(Ksp)

get S

S = mol/V = (mass/MW)/L = (8.8/321) = 0.0274 mol / L

Ksp = (0.0274^2)

Ksp = 0.00075076

Ksp = 7.5*10^-4

b)

if

Mn(OH)2 --> Mn+2 + 2OH-

this is type:

AB2 <--> A+2 + 2B- ;

Ksp = [A+2][B-]^2 = S* (2S)^2

Ksp = 4*S^3 -->

S = (Ksp/4)^(1/3)

S = ((2*10^-3)/4)^(1/3)

S = 0.07937 mol of Mn(OH)2 per liter

c)

get pOH, from [OH-]

pOH = 14-pH = 14-9.73 = 4.27

[OH-] = 10^-pOH = 10^-4.27 = 0.0000537

now,

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

4.87*10^-17 = ([Fe+2]) ( 0.0000537 ^2)

[Fe+2] < (4.87*10^-17) / ( 0.0000537 ^2)

[Fe+2] = < 1.688*10^-8 M