Review the following concepts if necessary:

- Concentration Units for AP Chemistry
- Electrolytes and Nonelectrolytes for AP Chemistry
- Colligative Properties for AP Chemistry
- Colloids for AP Chemistry

### Questions

### First Free-Response Question

You have 20 minutes to answer the following questions. You may not use a calculator. You may use the tables at the back of the book.

Five beakers each containing 100.0 mL of an aqueous solution are placed on a lab bench. The solutions are all at 25°C. Solution 1 contains 0.20 M KNO_{3}. Solution 2 contains 0.10 M BaCl_{2}. Solution 3 contains 0.15 M C_{2}H_{4}(OH)_{2}. Solution 4 contains 0.20 M (NH_{4})_{2}SO_{4}. Solution 5 contains 0.25 M KMnO_{4}.

- One of the solutions could oxidize two of the other solutions. Which solution is it? Which solutions could it oxidize?
- Which solution has the lowest pH? Explain.
- Which pair of solutions would give a precipitate if they are mixed? What is the formula for this precipitate?
- Which solution would be the poorest conductor of electricity? Explain.
- Rank the solutions in order of increasing boiling point. Explain.

### Second Free-Response Question

You have 20 minutes to answer the following questions. You may not use a calculator. You may use the tables in the back of the book.

Five beakers are placed in a row on a countertop. Each beaker is half filled with a 0.20 M aqueous solution. The solutes, in order, are: (1) potassium sulfate, (2) methyl alcohol, (3) sodium carbonate, (4) ammonium chromate, and (5) barium chloride. The solutions are all at 25°C.

Answer the following questions with respect to the five solutions listed above.

- Which solution will form a precipitate when ammonium chromate is added to it? Give the formula of the precipitate.
- Which solution is the most basic? Explain.
- Which solution will exhibit the lowest boiling-point elevation? Explain.
- Which solution is colored?
- Which of the other solutions will not react with solution (5), barium chloride?

### Answers and Explanations

### First Free-Response Question

- 1 point for picking solution 5, and 1 point for picking solutions 2 and 3.
- 1 point for picking solution 4, and 1 point for saying the ammonium ion (NH
_{4}^{+}) is a weak acid, or that it undergoes hydrolysis. - 1 point for picking solutions 2 and 4, and 1 point for BaSO
_{4}. - 1 point for picking solution 3, and 1 point for saying it is a non-electrolyte or that it does not ionize.
- 1 point for the order: 3 < 2 < 1 < 5 < 4, and 1 point for the explanation. The explanation must relate the order to the number (concentration) of solute particles in the solution.

There is a total of 10 points possible.

### Second Free-Response Question

- Solution (5) barium chloride will give a precipitate. The formula of the precipitate is BaCrO
_{4}. - Solution (3) sodium carbonate is the most basic. Since the carbonate ion is the conjugate base of a weak acid, it will undergo significant hydrolysis to produce a basic solution.
- Solution (2) methyl alcohol will show the least boiling point elevation. Methyl alcohol is the only nonelectrolyte.
- Solution (4) ammonium chromate is yellow.
- Solution (2) methyl alcohol is the only solution that will not form a precipitate with barium chloride.

You get 1 point for picking the correct solution, and 1 point for the correct formula for the precipitate.

You get 1 point for picking the correct solution, and 1 point for the correct explanation.

You get 1 point for picking the correct solution, and 1 point for the correct formula for the explanation.

You get 1 point for picking the correct solution.

You get 1 point for picking the correct solution.

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