AP Chemistry
Name: ___________________________
Group Members:
___________________________
___________________________
___________________________
Relating Equilibrium, pH,
and Solubility Product
Constant
Purpose and Objectives
Chemistry is presented often as a series of isolated topics having no relationship. In this lab you will
use a simple procedure for determining the pH of a saturated solution of a base as a means of
calculating an equilibrium constant (in this case, a solubility product constant) from your data. The
objective of this lab is to be able to obtain results in good agreement with published values.
Safety and Disposal
Normal laboratory precautions, including wearing goggles and aprons at all times, should be taken to
protect you at all times. The calcium and magnesium hydroxides can be rinsed down the sink with an
excess of water. Other metal hydroxides are more toxic and should be precipitated as solids. Solid waste
should be disposed of according to local regulations.
Equipment
100 mL beaker
Spatula or Scoop
balance
Stirring Rod
distilled water
pH meter/paper (0.2-0.3 pH)
Hot plate (optional)
thermometer (optional)
Samples: Ca(OH)2 , Mg(OH)2, Ba(OH)2, and other metal doubly charged hydroxides
AP Chemistry
Procedure
1. You will prepare saturated solutions of the metal hydroxides by dissolving 1 g of the base in
50 mL of distilled water.
2. After brief stirring, the solution is allowed to stand 3 to 5 minutes and the pH of the
solutions. The pH should be measured within 5 minutes to minimize the effect of dissolving
atmospheric CO2.
3. To determine pH, place a drop or two of the solution off a stirring rod onto the pH paper.
4. Using the value of the pH of the solution, determine Ksp.
5. Repeat using other metal hydroxides as time permits.
6. (Optional) If time permits, you may vary the temperature and determine pH and solubility
for several temperatures.
AP Chemistry
Name: ___________________________
RELATING EQUILIBRIUM, pH, AND SOLUBILITY PRODUCT CONSTANT
PRE-LAB DATA SHEET
1. Write the equilibrium equation and the Ksp expressions for the following:
a. Calcium hydroxide
b. Aluminum hydroxide
c. Lead sulfate
d. Barium phosphate
2. Calculate the pH, [H3O+] and [OH-] of the following:
a. 0.1 M NaOH
b. 0.01 M CH3COOH (Ka = 1.8 x 10 -5)
c. 1 M HCl
d. 0.1 M CH3NH2 (Kb = 4.4 x 10-5)
3. The solubility of lead chromate, PbCrO4, in water is 4.4 x 10-5 g/L. Calculate the solubility in
moles/L and calculate Ksp.
4. The pH of a saturated solution of manganese hydroxide, Mn(OH)2, is 9.1. Write the
equilibrium equation expression for Ksp. Calculate [H3O+], [OH-], and [Mn2+] and then
calculate Ksp.
5. In a saturated solution of cadmium sulfide, CdS, the [Cd2+] is 8.0 x 10-15 M. Calculate Ksp.
AP Chemistry
Name: ___________________________
Group Members:
___________________________
___________________________
___________________________
RELATING EQUILIBRIUM, pH, AND SOLUBILITY PRODUCT CONSTANT
LAB REPORT FORM
Data
You will need to construct data tables to display values. Your data tables will depend on the
proposed procedure used in class.
Data Analysis
1. What effect would the dissolving of large amounts of atmospheric carbon dioxide have on
the measured pH? On the calculated Ksp? Why?
2. The solubility product constant for Pb(OH)2 is 2.8 x 10-16. Write the Ksp expression, calculate
the pH, [H3O+] and [OH-] of a saturated solution of Pb(OH)2. Suggest a reason you did not
use this compound.
3. Suppose that instead of using distilled water, you had mistakenly used 1 x 10-4 M NaOH.
How would that have affected the solubility of the bases used? What effect would that have
had on the calculated values of Ksp?
Conclusion
You will need to write a proper conclusion relating what you saw in the lab and how it relates to the
topics covered in class. Be specific in your relation of observations to the results. Be sure to include
any possible sources of error with a discussion of how that error could have affected the results.