1. Chapter 13 Reaction Rates and Chemical Equilibrium
13.6 Equilibrium in Saturated Solutions
Learning Goal Write the solubility product expression for a slightly soluble salt and calculate the Ksp; use Ksp to determine the solubility.
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2. Equilibrium Systems in Solutions
Equilibrium systems also include aqueous saturated solutions between solid solutes of slightly soluble salts and their ions, such as
a slightly soluble salt such as calcium phosphate Ca3(PO4)2, found in bones
Ca3(PO4)2(s) Ca2+(aq) + 2PO43−(aq)
a slightly soluble salt such as calcium oxalate CaC2O4, found in kidney stones
CaC2O4(s) Ca2+(aq) + C2O42−(aq)
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3. In a saturated solution
Solubility Product
In a saturated solution
a solid, slightly soluble salt is in equilibrium with its ions
at constant temperature, the concentration of the ions in the saturated solution is constant
Calcium oxalate, a slightly soluble salt, produces small amounts of Ca2+ and C2O42− in aqueous solution.
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4. CaC2O4(s) Ca2+(aq) + C2O42−(aq) Ksp = [Ca2+][C2O42−]
Solubility Product
The solubility of a salt is the quantity that dissolves to form a saturated solution, represented by Ksp.
CaC2O4(s) Ca2+(aq) + C2O42−(aq)
Ksp = [Ca2+][C2O42−]
Ca3(PO4)2(s) Ca2+(aq) + 2PO43−(aq)
Ksp = [Ca2+]3[PO43−]2
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5. Write a Ksp expression for the slightly soluble salt, Ag2CO3(s).
Learning Check
Write a Ksp expression for the slightly soluble salt, Ag2CO3(s).
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6. Write a Ksp expression for the slightly soluble salt, Ag2CO3(s).
Solution
Write a Ksp expression for the slightly soluble salt, Ag2CO3(s).
Write the solid salt on the left and the aqueous ions on the right:
Ag2CO3(s) Ag+(aq) + CO32− (aq)
The solubility product expression is written as the product of the molar concentration of the ions.
Ksp = [Ag+]2[CO32−]
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7. Solubility Product Constant
The numerical value of the solubility product expression is the solubility product constant, Ksp.
Solubility is expressed as the molar solubility, which is the moles of solute that dissolve in 1 liter of saturated solution.
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8. Guide to Calculating Ksp
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9. Learning Check
We can make a saturated solution of CaCO3 by adding solid CaCO3 to water and stirring until equilibrium is reached.
What is the numerical value of Ksp for CaCO3 if the equilibrium mixture contains and
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10. What is the numerical value of Ksp for CaCO3 if
Solution
What is the numerical value of Ksp for CaCO3 if
the equilibrium mixture contains
Step 1 State the given and needed quantities.
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11. What is the numerical value of Ksp for CaCO3 if
Solution
What is the numerical value of Ksp for CaCO3 if
the equilibrium mixture contains
Step 2 Write the equilibrium equation for the dissociation of the slightly soluble salt.
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12. What is the numerical value of Ksp for CaCO3 if
Solution
What is the numerical value of Ksp for CaCO3 if
the equilibrium mixture contains
Step 3 Write the solubility product expression (Ksp).
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13. What is the numerical value of Ksp for CaCO3 if
Solution
What is the numerical value of Ksp for CaCO3 if
the equilibrium mixture contains
Step 4 Substitute the molar concentration of each ion into the Ksp expression and calculate.
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14. Solubility Product Constants
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15. The molar solubility, S, of a slightly soluble salt
is the number of moles of solute that dissolves in 1 liter of solution
for example, the molar solubility of CdS, is found experimentally to be
If we know the Ksp, we can determine the molar solubility.
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16. Guide to Calculating Molar Solubility from Ksp
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17. Calculate the molar solubility, S, of CdS if it has a
Learning Check
Calculate the molar solubility, S, of CdS if it has a
Cadmium sulfide is a slightly soluble salt.
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18. Calculate the molar solubility, S, of CdS if it has a
Solution
Calculate the molar solubility, S, of CdS if it has a
Step 1 State the given and needed quantities.
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19. Calculate the molar solubility, S, of CdS if it has a
Solution
Calculate the molar solubility, S, of CdS if it has a
Step 2 Write the equilibrium equation for the dissociation of the slightly soluble salt.
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20. Calculate the molar solubility, S, of CdS if it has a
Solution
Calculate the molar solubility, S, of CdS if it has a
Step 3 Write the solubility product expression, Ksp, using S.
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21. Calculate the molar solubility, S, of CdS if it has a
Solution
Calculate the molar solubility, S, of CdS if it has a
Step 4 Calculate the molar solubility S.
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22. Solubility, Adding a Common Ion
When MgCO3, a slightly soluble salt, dissolves in water, small amounts of Mg2+ and CO32− ions are produced in equal amounts.
The Ksp and molar solubility for MgCO3 are:
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23. Solubility, Adding a Common Ion
When we add a soluble salt, MgCl2 to the solution, it dissolves into Mg2+ and 2Cl− ions,
increases the concentration of Mg2+ in the solution, and shifts the equilibrium of the reaction to the left, decreasing the amount of ions produced.
MgCO3(s) Mg2+(aq) + CO32−(aq)
Mg2+ added
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24. Solubility, Adding a Common Ion
When we add a soluble salt, Na2CO3 to the solution, it dissolves into 2Na+ and CO32− ions, increases the concentration of CO32− in the solution, and shifts the equilibrium of the reaction to the left, decreasing the amount of ions produced.
MgCO3(s) Mg2+(aq) + CO32−(aq)
CO32− added
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25. Indicate the shift in equilibrium of each change:
Learning Check
Indicate the shift in equilibrium of each change:
PbSO4(s) Pb2+(aq) + SO42−(aq)
toward products 2) toward reactants
adding SO42−
adding Pb2+
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26. Indicate the shift in equilibrium of each change:
Solution
Indicate the shift in equilibrium of each change:
PbSO4(s) Pb2+(aq) + SO42−(aq)
toward products 2) toward reactants
adding SO42− ) toward reactants
adding Pb ) toward reactants
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27. A. increases the solubility of the salt
Learning Check
Adding a common ion to a saturated solution of a slightly soluble salt has what effect on the solubility product expression, Ksp?
A. increases the solubility of the salt
B. does not change the solubility of the salt
C. decreases the solubility of the salt
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28. C. decreases the solubility of the salt
Solution
Adding a common ion to a saturated solution of a slightly soluble salt has what effect on the solubility product expression, Ksp?
C. decreases the solubility of the salt
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29. Concept Map
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