REVIEW EXERCISES

General Review

Write a brief and clear answer to each question. Be sure to show your work.

Question 1

1. Write the reversible reactions for these processes.

  1. Chlorine gas becomes liquid chlorine.

  2. Nitrogen dioxide becomes dinitrogen tetroxide.

  3. Silver chloride precipitates from aqueous solution. Water evaporates.

Question 2

2. Write the equilibrium-constant equations for the processes in Exercise 1.

Question 3

3. Write two statements that are always true of a system at equilibrium.

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Question 4

4. When a dissolving and precipitation process is at equilibrium, the solution is saturated. Explain why this is true.

Question 5

5. What is the concentration of copper ion, Cu2+, in an aqueous solution of copper (II) carbonate, CuCO3, if Ksp = 1.4 × 10−10 at 25 ºC?

Question 6

6. What does an acid-base indicator have to do with equilibrium?

Question 7

7. The chemical equation for the dissolution of lead chloride, PbCl2(s), in water is given here.

PbCl2(s) ↔ Pb2+(aq) + 2Cl−(aq)

Determine the concentration of Pb2+ ions in a saturated PbCl2 solution if Ksp = 1.7 × 10−5.

Question 8

8. Solid lead (II) sulfate, PbSO4, is dissolved in water to form a solution with excess undissolved solute at the bottom of the container. The value of Ksp for lead sulfate is 2.5 × 10−8.

  1. How can you tell that this solution is saturated?

  2. Is the solution at equilibrium? How do you know?

  3. Write the chemical equation for the reversible change that is taking place.

  4. What is the equilibrium-constant equation for this equilibrium?

  5. What is the equilibrium concentration of each ion?

  6. Dissolving lead (II) sulfate is an endothermic change. Predict what will happen to the value of [Pb2+] and [SO42−] if the solution is heated.

  7. What would happen if you added more sulfate ions to the solution?

Question 9

9. The value of Ksp for cadmium sulfide, CdS, is 8.0 × 10−27. Compare this value with the Ksp for lead (II) sulfate given in Exercise 8.

  1. Which compound will have a higher concentration of ions in solution at equilibrium? Explain your reasoning.

  2. Calculate the concentration of cadmium ions in solution at equilibrium.

Question 10

10. For the acid-base indicator litmus, the molecule, HIn(aq), is red and the anion, In−(aq), is blue.

  1. Write a reaction for the dissociation of the HIn molecule in solution.

  2. Why is litmus purple when you dissolve it in water? Explain your reasoning.

  3. What color do you think litmus is in a basic solution? Use Le Châtelier’s principle to explain your thinking.