Concept Test 6

Question 1

can be thought of as the conjugate base of the strong acid from HCl. If equal amounts of and ( = ) are added together this mixture will:

a. be a buffer.
b. be a buffer whose pH = [H^+].
c. not be a buffer.

The three questions below refer to these four qualitative pictures of pH vs. volume of acid or base added.

1.

2.

3.

4.

Question 2

The appropriate diagram showing what happens to pH vs. added volume as HCl is added to pure water is:

1.
2.
3.
4.

Reason for Answer:

Question 3

The appropriate diagram showing what happens to pH vs. added volume as HCl is added to an acetate/acetic acid mixture whose concentration ratio is about 1 is:

1.
2.
3.
4.

Reason for Answer:

Question 4

The appropriate diagram showing what happens to pH vs. added volume as strong base, OH^-, is added to an acetate/acetic acid mixture whose concentration ratio is about 1 is:

1.
2.
3.
4.

Reason for Answer:

Question 5

We are asked by a chemistry student at Yale to prepare a buffer in the range pH = 7 using lactic acid (pKa = 3.86). After due consideration we tell them they should be able to figure this out themselves but that:

a. This is a good idea because the ratio [lactate]/[lactic acid] is around 1.
b. This is a poor idea because the ratio [lactate]/[lactic acid] is a large number.
c. This is a poor idea because the ratio [lactate]/[lactic acid] is a small number.

Question 6

The buffering capacity, the total number of moles of acid the buffer can control, depends on

a. the ratio of conjugate base to weak acid.
b. the pKa of the weak acid.
c. the amount of weak acid and conjugate base present.

Question 7

The transfer of fron arterial blood to venous blood increases by 0.00169M. From for each bicarbonate there is one hydrogen ion. Therefore, the expected pH of the venous blood serum is:

a. pH > 2.8.
b. pH = 2.8.
c. pH < 2.8

Reason for Answer:

Question 8

The following table shows the acidic components of Colombian Dark Roast coffee. The pH of the coffee is found to be pH = 5.23. Assuming that the taste of the coffee is due to the amount of conjugate base present from natural acids, which component do you think provides the majority of the taste (the majority concentration of conjugate base of these weak acids)?

ACID	Citric	Malic	Lactic	Pyruvic	Acetic
% Composition	0.018	0.018	0.077	0.051	0.072
pKa1	3.09	6.26	3.86	2.50	4.76

Citric
Malic
Lactic
Pyruvic
Acetic

Reason for Answer:

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