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ScrubsFan
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69. Calculate the Ksp for each of the salts whose solubility is listed below.
a) CaSO4 = 3.3 x 10-3 mol/L
b) MgF2 = 2.7 x 10-3 mol/L
Answers:
a) Solution
1. Write the dissociation reaction and the Ksp expression for the equilibrium reaction. Thus,
CaSO4(s) <---> Ca2+ (aq) + SO42- (aq)
Ksp = [Ca2+][SO42-]
2. Calculate the concentrations of the ions at equilibrium from the stoichiometric information provided in the equilibrium equation. The equation shows that 1 mol of CaSO4 produces 1 mol of Ca2+ and 1 mol of SO42- at equilibrium. Therefore,
[Ca2+] = 3.3 x 10-3 mol/L
[ SO42-] = 3.3 x 10-3 mol/L
3. Substitute the concentrations into the Ksp expression:
Ksp = (3.3 x 10-3)( 3.3 x 10-3)
= 1.2 x 10-5
b) MgF2 <---> Mg2+ (aq) + F22+ (aq)
Ksp = [Mg2+][F22+]
[Mg2+] = 2.7 x 10-3
[F22+] = 2.7 x 10-3
Ksp = (2.7 x 10-3)(2.7 x 10-3)
= 7.3 x 10-6
a) CaSO4 = 3.3 x 10-3 mol/L
b) MgF2 = 2.7 x 10-3 mol/L
Answers:
a) Solution
1. Write the dissociation reaction and the Ksp expression for the equilibrium reaction. Thus,
CaSO4(s) <---> Ca2+ (aq) + SO42- (aq)
Ksp = [Ca2+][SO42-]
2. Calculate the concentrations of the ions at equilibrium from the stoichiometric information provided in the equilibrium equation. The equation shows that 1 mol of CaSO4 produces 1 mol of Ca2+ and 1 mol of SO42- at equilibrium. Therefore,
[Ca2+] = 3.3 x 10-3 mol/L
[ SO42-] = 3.3 x 10-3 mol/L
3. Substitute the concentrations into the Ksp expression:
Ksp = (3.3 x 10-3)( 3.3 x 10-3)
= 1.2 x 10-5
b) MgF2 <---> Mg2+ (aq) + F22+ (aq)
Ksp = [Mg2+][F22+]
[Mg2+] = 2.7 x 10-3
[F22+] = 2.7 x 10-3
Ksp = (2.7 x 10-3)(2.7 x 10-3)
= 7.3 x 10-6