1. 9.3 Solubility Gout primarily affects adult men over the age of 40.
Attacks of gout may occur when the concentration of uric acid in blood plasma exceeds its solubility of 7 mg/100 mL of plasma at 37 °C.
Learning Goal Define solubility; distinguish between an unsaturated and a saturated solution. Identify an ionic compound as soluble or insoluble.

2. Solubility
Solubility is
the maximum amount of solute that dissolves in a specific amount of solvent.
temperature sensitive for solutes.
expressed as grams of solute in 100 grams of solvent, usually water.

3. Unsaturated Solution Unsaturated solutions
contain less than the maximum amount of solute.
can dissolve more solute.

4. Saturated Solution Saturated solutions
contain the maximum amount of solute that can dissolve.
have undissolved solute at the bottom of the container.
contain solute that dissolves as well as solute that recrystallizes in an equilibrium process.

5. Saturated Solution
More solute can dissolve in an unsaturated solution but not in a saturated solution.

6. Study Check
Identify each of the following solutions as saturated or unsaturated.
A. Salt disappears when put in water.
B. Sugar added to a cup of water does not disappear, but sits at the bottom of the cup.

7. Solution
Identify each of the following solutions as saturated or unsaturated.
A. Unsaturated: Salt disappears when put in water.
B. Saturated: Sugar added to a cup of water does not disappear, but sits at the bottom of the cup.

8. Study Check
At 40 C, the solubility of KBr is 80 g/100 g of H2O. Identify the following solutions as either saturated or unsaturated. Explain.
A. 60 g KBr added to 100 g of water at 40 C
B g KBr added to 200 g of water at 40 C
C. 25 g KBr added to 50 g of water at 40 C

9. Solution
At 40 C, the solubility of KBr is 80 g/100 g of H2O. Identify the following solutions as either saturated or unsaturated. Explain.
A. Unsaturated: 60 g KBr/100 g of water at 40 C is less than the solubility of KBr in water (80 g KBr/100 g water).
B. Saturated: 200 g KBr/200 g of water at 40 C is greater than the solubility of KBr in water (80 g KBr/100 g water).
C. Unsaturated: 25 g KBr/50 g of water at 40 C is less than the solubility of KBr in water (80 g KBr/100 g water).

10. Effect of Temperature on Solubility
depends on temperature.
of most solids increases as the temperature increases.
of gases decreases as the temperature increases.
In water, most common solids are more soluble as the temperature increases.

11. Effect of Temperature on Solubility
The solubility of gases decreases as the temperature of the solution increases.

12. Study Check
1. Why could a bottle of carbonated drink possibly burst (explode) when it is left out in the hot sun?
2. Why do fish die in water that is too warm?

13. Solution
1. The pressure in a bottle increases as the gas leaves solution when it becomes less soluble at higher temperatures. As pressure increases, the bottle could burst.
2. Because O2 gas is less soluble in warm water, fish cannot obtain the amount of O2 required for their survival.

14. Solubility and Pressure
Henry’s law states that
the solubility of a gas in a liquid is directly related to the pressure of that gas above the liquid.
at higher pressures, more gas molecules dissolve in the liquid.
When the pressure of a gas above a solution decreases, the solubility of that gas in the solution also decreases.

15. Soluble vs. Insoluble Ionic Compounds
Only ionic compounds that contain a soluble cation or anion are soluble in water.
In an insoluble ionic compound, the ionic bonds are too strong for the polar water molecules to break. We can use the solubility rules to predict whether an ionic compound would be expected to dissolve in water.

16. Soluble vs. Insoluble Ionic Compounds
Mixing certain aqueous solutions produces insoluble ionic compounds.
If an ionic compound contains a combination of a cation and an anion that are not soluble, that ionic compound is insoluble. For example, combinations of cadmium and sulfide, iron and sulfide, lead and iodide, and nickel and hydroxide do not contain any soluble ions. Thus, they form insoluble ionic compounds.
Core Chemistry Skill Using Solubility Rules

17. Soluble vs. Insoluble Ionic Compounds
Sulfates, SO42−, are soluble unless combined with Ba2+, Pb2+, Ca2+, Sr2+, or Hg22+.
Barium sulfate, BaSO4, an insoluble ionic compound, is used to enhance X-rays.
Core Chemistry Skill Using Solubility Rules

18. Using Solubility Rules

19. Study Check
Predict if the following compounds are soluble or insoluble. Explain why.
A. CdS
B. Na2SO4
C. PbI2
D. Ni(NO3)2

20. Solution
Predict if the following compounds are soluble or insoluble. Explain why.
A. CdS Insoluble; S2− compounds are generally insoluble.
B. Na2SO4 Soluble; Na+ compounds are always soluble.
C. PbI2 Insoluble; I− is soluble unless combined with Pb2+.
D. Ni(NO3)2 Soluble; NO3− compounds are always soluble.

21. Guide to Writing an Equation for the Formation of a Solid
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.

22. Study Check
We can use solubility rules to predict whether a solid, called a precipitate, forms when two solutions of ionic compounds are mixed.
What precipitate forms when solutions of Pb(NO3)2 and K2SO4 are mixed?

23. Solution
We can use solubility rules to predict whether a solid, called a precipitate, forms when two solutions of ionic compounds are mixed.
What precipitate forms when solutions of Pb(NO3)2 and K2SO4 are mixed?
STEP 1 Write the ions of the reactants.
Reactants, initial combinations:
Pb2+(aq) NO3−(aq)
K+(aq) SO42−(aq)

24. Solution
We can use solubility rules to predict whether a solid, called a precipitate, forms when two solutions of ionic compounds are mixed.
What precipitate forms when solutions of Pb(NO3)2 and K2SO4 are mixed?
STEP 2 Write combinations of ions and determine if any are insoluble.
Mixture Product Soluble

25. Solution
We can use solubility rules to predict whether a solid, called a precipitate, forms when two solutions of ionic compounds are mixed.
What precipitate forms when solutions of Pb(NO3)2 and K2SO4 are mixed?
STEP 3 Write the ionic equation including any solid.
Pb2+(aq) + SO42−(aq) + 2K+(aq) + 2NO3−(aq) 
PbSO4(s) + 2K+(aq) + 2NO3−(aq)

26. Solution
We can use solubility rules to predict whether a solid, called a precipitate, forms when two solutions of ionic compounds are mixed.
What precipitate forms when solutions of Pb(NO3)2 and K2SO4 are mixed?
STEP 4 Write the net ionic equation.
Remove the spectator ions Pb2+(aq) + SO42−(aq) + 2K+(aq) + 2NO3−(aq) 
PbSO4(s) + 2K+(aq) + 2NO3−(aq)
Pb2+(aq) + SO42−(aq)  PbSO4(s)