a) The solubility of silver sulfate, Ag 2 SO 4 , in water has been determined to

Question

a)

The solubility of silver sulfate, Ag2SO4, in water has been determined to be 8.0 g/L. What is the solubility of silver sulfate in 0.800M of sodium sulfate, Na2SO4?

= _____g/L

b)

Calculate the solubility of strontium sulfate, SrSO4, in 7.90E-2M of sodium sulfate, Na2SO4. Solve the equation exactly. Ksp(SrSO4) = 2.5E-7

=_____g/L

c)

Magnesium sulfate, MgSO4, is added to 449 mL of 8.50E-2M sodium hydroxide, NaOH, until precipitate just forms. How many grams of magnesium sulfate were added? Assume that the volume of the solution is not changed significantly by the addition of magnesium sulfate.
Ksp Mg(OH)2 = 1.8E-11

= _____g

Explanation / Answer

a) Ksp for Ag2SO4 = [Ag+]^2[SO4^2-]

Ksp for Na2SO4 = [Na+]^2[SO4]

The molar mass of Ag2SO4 is: 311.8 g/mol. Hence, 8.0 g/L is equivalent to (8.0/311.8) M or 0.02566 M concentration.
Ksp = [Ag+]^2[SO4--] = (2*0.02566)^2*0.02566 = 6.756*10^-5 (M^3)

Let the solubility of silver sulfate, Ag2SO4, in 0.8 M sodium sulfate, Na2SO4, be X M. We have:
Ksp = 6.756*10^-5 = (2*X)^2(0.8+X)
or: X = 0.0038 (M)
Hence the solubility of silver sulfate, Ag2SO4, in 0.8 M sodium sulfate, Na2SO4, is:
0.00380*311.8 = 1.18 (g/L)

b) Ksp Na2SO4 = 1.1968 x 10^ -3 = [Na+]^2[SO4]

2.5 x 10^-7 = x^2

x = 5 x 10^-4 M = [SO4^2-]

1.1968 x 10^-3 = (2 x 7.9 x 10^-2)^2(5x10^-4+x)

0.048 = 5x10^-4+x

x = 0.0475 g/M

c) Ksp = [Mg2+][OH-]^2

1.8 x 10^-11 = [Mg2+](0.085)^2

[Mg2+] = 2.49 x 10^-5 M

moles of MgSO4 = 0.449 x 2.49 x 10^-5 = 1.118 x 10^-5 moles

grams of MgSO4 = 1.118 x 10^-5/120.366 = 9.29 x 10^-8 g

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