a) Ammonia, NH 3 , is a base that ionizes to give NH 4 + and OH - (K b = 1.8E-5)

Question

a)

Ammonia, NH3, is a base that ionizes to give NH4+ and OH- (Kb = 1.8E-5). You add magnesium sulfate to an ammonia solution. Calculate the concentration of Mg2+ ion when magnesium hydroxide, Mg(OH)2, just begins to precipitate from 0.220 M NH3. The Ksp for Mg(OH)2 is 1.8E-11.

[Mg2+] = _____M

b)

You add 50.0 mL of 0.116 M HCl to 50.0 mL of 0.116 M AgNO3. What are the final concentrations of H3O+ and Cl- in the solution? (Ksp(AgCl) = 1.8E-10)

[H3O+] = _____M

[Cl-] = _____M

c)

A researcher found the solubility of lead(II) chloride in 0.430 M NaCl to be 2.41E-2 g/L. What is the solubility product of lead(II) chloride?

Ksp = _____

Explanation / Answer

a) Kb = [NH4+][OH-]/[NH3]

1.8 x 10^-5 = x^2/0.22

x = [OH-] = 1.99 x 10^-3 M

Ksp = [Mg2+][OH-]^2 = [Mg2+][1.99 x 10^-3 x 2]^2

[Mg2+] = 1.131 x 10^-6 M

b) M of HCl in 100 ml of solution = 0.05 x 0.116 / 0.1 = 0.058 M

M og AgNO3 in 100 mL of solution = 0.05 x 0.116 / 0.1 = 0.058 M

Ksp = [Ag+][Cl-] = 1.8 x 10^-10 = (0.058)[Cl-]

[Cl-] = 3.1 x 10^-9 M

[H3O+] = 0.058 M

c) A researcher found the solubility of lead(II) chloride in 0.430 M NaCl to be 2.41E-2 g/L. What is the solubility product of lead(II) chloride.

Ksp = [Pb2+][Cl-]^2

[Cl-] = 0.43 M

[Pb2+] = 2.41 x 10^-2 g/L = 2.41 x 10^-2/58.44 = 4.12 x 10^-4 M

Ksp of PbCl2 = (4.12 x 10^-4)(0.43)^2 = 7.62 x 10^-5

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