AP Chemistry Practice Test 38

1. At constant temperature, a change in the volume of the system will NOT affect the moles of the substances present in which of the following?

Questions 2-6 refer to the following information.

pH versus volume of titrant added

Ascorbic acid (vitamin C), H2C6O6, is a diprotic acid used as a dietary supplement. As with all dietary supplements, it is important to analyze samples for purity. The vitamin C may be extracted from natural sources or synthesized. The extraction vitamin C may contain additional extracted ingredients to which some people are allergic. Synthetic vitamin C may contain other forms of the vitamin; however, modern synthetic methods do not generate this contaminate. The above titration curve is an idealized graph for a diprotic acid. On this graph, E and F represent the pH at the endpoints with the possibility that E may shift slightly and one or the other may not be present. H is the volume of base required to titrate the first hydrogen ion and G is the quantity of base necessary to titrate both hydrogen ions. G is twice H.

2. What is the approximate pH at ½ H?

3. If G were not twice H, what would this indicate?

4. Which of the following bases would be the best choice for the titration?

5. In the titration of a sample of vitamin C, what is the approximate value of F?

6. While the titration of a diprotic acid to produce a curve similar to the idealized one above is useful in many analyses, ascorbic acid is not a good candidate for this type of analysis. Why?

7. Which of the following CANNOT behave as both a Brønsted base and a Brønsted acid?

8. A student mixes 50.0 mL of 0.10 M potassium chromate, K2CrO4, solution with 50.0 mL of 0.10 M AgNO3. A red precipitate of silver chromate forms and the concentration of the silver ion becomes very small. Which of the following correctly places the concentrations of the remaining ions in order of decreasing concentration?

9. There are a number of experiments for the determination of the molecular mass of a gas. One method begins by heating a solid or liquid in a flask to produce a gaseous product. The gas passes through a tube and displaces water in an inverted, water-filled bottle. The mass of the starting material is measured, along with the volume of the displaced water and the temperature of the system. The pressure in the inverted water-filled bottle is equal to the external pressure. Once the barometric pressure has been recorded, what other information is needed to finish the experiment?


Using the information given above, calculate the enthalpy change for the following reaction:

2 C(s) + H2(g) → C2H2(g)

11. Cerium(III) sulfate, Ce2(SO4)2, is less soluble in hot water than it is in cold. Which of the following conclusions may be related to this?