5 Steps to a 5 AP Chemistry 2019

AP Chemistry Practice Exam 1 ❮ 313

Use the following information for questions 10–12.

Acid Ka, Acid Dissociation Constant

HIO 3 1.7 × 10 -^1

HIO 4 2.8 × 10 -^2

HNO 2 4.5 × 10 -^4

HCN 6.2 × 10 -^10

10. A buffered solution with a pH near 5 is needed
    for an experiment. Using the above information,
    which of the combinations would be the best
    choice to prepare the buffer?
    (A) HIO 3 + KIO 3
    (B) HCN + KCN
    (C) HNO 2 + KNO 2
    (D) HIO 4 + NaIO 4


11. A student wishes to measure the pH of a 0.10 M
    solution of the sodium salt of each of the acids
    in the table. These salts are NaIO 3 , NaIO 4 ,
    NaNO 2 , and NaCN, respectively. Which of the
    four salt solutions will have the highest pH?
    (A) NaIO 3
    (B) NaIO 4
    (C) NaNO 2
    (D) NaCN


12. Which of the acids in the table would be the
    easiest to titrate with a weak base like ammonia
    (Kb = 1.8 × 10 –5)?
    (A) HIO 3
    (B) HIO 4
    (C) HNO 2
    (D) HCN

Use the following information to answer questions

13 - 17.

pH versus volume of titrant added

0H G

F

pH

Volume strong acid added

E

H 2 C 6 O 6 Ka1 = 8.0 × 10 -^5 Ka2 = 1.6 × 10 -^12

Ascorbic acid (vitamin C), H 2 C 6 O 6 , 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 addi-

tional 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 shown 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 pres-

ent. 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.

13. What is the approximate pH at ½ H?
    (A) 7
    (B) 5
    (C) 2
    (D) Impossible to predict


14. If G were not twice H, what would this indicate?
    (A) There is a contaminant that is either an acid
    or a base.
    (B) The other form of vitamin C is present.
    (C) The vitamin C was extracted from a plant.
    (D) The vitamin C is synthetic.


15. Which of the following bases would be the best
    choice for the titration?
    (A) Al(OH) 3
    (B) Na 2 CO 3
    (C) NH 3
    (D) KOH


16. In the titration of a sample of vitamin C, what is
    the approximate value of F?
    (A) < 7
    (B) > 7
    (C) = 7
    (D) Unknown

GO ON TO THE NEXT PAGE

20-Moore_PE01_p307-340.indd 313 31/05/18 1:58 pm