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178 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 17
The molar solubility of PbF 2 in water at 25°C is
2.0 ϫ 10 Ϫ3 mol/L.
b. As shown above, the fluoride ion concentration in a saturated
solution of PbF 2 at 25°C is as follows.
[F Ϫ ] ϭ 2s ϭ 2(2.0 ϫ 10 Ϫ3 mol/L) ϭ 4.0 ϫ 10 Ϫ3 mol/L
Practice Problems
12. Use the data in Table 17-3 in your textbook to calculate the
solubility in mol/L of these ionic compounds at 298 K.
a. MgCO 3
b. AlPO 4
c. Ag 2 SO 4
d. Al(OH) 3
13. Use the data in Table 17-3 in your textbook to calculate the
following ion concentrations at 298 K.
a. [Ba 2ϩ ] in a saturated solution of BaCrO 4
b. [CO 3
2Ϫ ] in a solution of ZnCO 3 at equilibrium
c. [Cl Ϫ ] in a solution of PbCl 2 at equilibrium
d. [Mg 2ϩ ] in a saturated solution of Mg 3 (PO 4 ) 2
Predicting precipitates The solubility product constant expression can also be used to predict whether a precipitate will form
when two solutions of ionic compounds are mixed. The molar
concentrations of the ions in a solution are used to calculate the ion
product, Q sp . If Q sp Ͼ K sp , a precipitate will form, reducing the
ion concentrations until the system reaches equilibrium and the
solution is saturated. If Q sp Ͻ K sp , no precipitate forms. The
following example problem demonstrates how to use Q sp and K sp
to determine whether a precipitate will form.
Example Problem 17-6
Predicting a Precipitate
Predict whether a precipitate will form if 200 mL of 0.030M CaCl 2
is added to 200 mL of 0.080M NaOH.
A double-replacement reaction might occur according to this
equation.
CaCl 2 ϩ 2NaOH 3 2NaCl ϩ Ca(OH) 2
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