Le Chatelier's Principle


Answer the pre-lab questions seen below on your Report Sheet.

1. Which describes a solution that contains a system at equilibrium? Explain your answer.
One in which the color of the solution is changing slowly, or one in which the color is not changing.

2. The following equilibrium is established when copper ions and bromide ions are placed in solution.

heat + Cu(H2O)6+2 + 4 Br- 6 H2O + CuBr4-2

The tube on the left contains only copper sulfate dissolved in solution. The tube on the right is the result of adding some potassium bromide solution. Given that the Cu(H2O)6+2 ion is blue and that the CuBr4-2 ion is green, answer the questions below.


a. What happened to the concentration of each of the ions when the KBr was added?

b. Explain why the solution changed color.

c. Would the tube feel hot or cold when the KBr was added?


3. Consider the following equilibrium.

Mg(OH)2(s) Mg+2 + 2 OH-

The tube on the left contains Mg(OH)2(s) and water. A chemical has been added to cause the change shown in the tube on the right. Suggest a possibility for what chemical could have been added.


4. Methanol has the formula CH3OH and can be produced by the reaction of carbon monoxide with hydrogen gas.

CO + 2 H2 CH3OH + heat

In an attempt to maximize the yield of methanol (amount of methanol produced), a chemist would try to shift the equilibrium as far to the right as possible. Which of the following would accomplish this?
    a. heating the mixture
    b. adding an excess of carbon monoxide
    c. removing the methanol as it is formed
    d. adding a substance that reacts with carbon monoxide

This completes the pre-lab. You may begin the experiment.

Report Sheet

pre-lab experiment post-lab

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