Question 1

Which of the following statements best explains why a carboxylic acid (pK$$_a = 4.5) is $$more acidic than a phenol (pK$$_a = 10$$)?

Accepted Answer

Carboxylic acids have a lower pK$$_a$$ because their conjugate base is stabilized by resonance and inductive effects.

Question 2

A pharmacist is preparing a solution of a weak acid drug (pK$$_a = 5.0). At $$which pH will the drug be MOST water-soluble?

Accepted Answer

pH 7.0

Question 3

Which of the following functional groups is expected to have the highest pK$$_a$$ value?

Accepted Answer

Phenol

Question 4

A drug contains an aniline group (pK$$_a$$ ≈ 5). At physiological pH (7.4), what is the expected charge state of this group?

Accepted Answer

Mostly uncharged (neutral)

Question 5

Which of the following substituents will INCREASE the acidity of a benzoic acid derivative?

Accepted Answer

A nitro group at the para position

Question 6

Using the Henderson-Hasselbalch equation, calculate the ratio of ionized to unionized form for a weak acid (pK$$_a = 4) at pH 6.$$

Accepted Answer

$$\frac{[A^-]}{[HA]} = 100$$

Question 7

Which of the following best describes the membrane permeability of a weak base (pK$$_a = 8) in $$the stomach (pH = 2)?

Accepted Answer

Low permeability due to high ionization

Question 8

A solution contains a weak base (pK$$_a = 9). $$What percent of the base is ionized at pH 7?

Accepted Answer

99%

Question 9

Which of the following is TRUE regarding the solubility of a weak acid drug as pH increases above its pK$$_a$$?

Accepted Answer

Total solubility increases due to increased ionization

Question 10

A zwitterionic ampholyte has pK$$_a($$acid) = 2.5 and pK$$_a($$base) = 9.5. At pH 7, what is the net charge of the molecule?

Accepted Answer

Zero (zwitterion dominates)

Question 11

Which of the following is a correct application of the Henderson-Hasselbalch equation for a weak base?

Accepted Answer

$$pH = pK_a + \log \frac{[B]}{[BH^+]}$$

Question 12

A drug with a sulfonamide group (pK$$_a = 10) is $$administered orally. In which part of the GI tract will it be MOST unionized?

Accepted Answer

Stomach (pH = 2)

Question 13

Which of the following is NOT a reason to use a salt form of a drug?

Accepted Answer

To increase the drug's chemical reactivity

Question 14

A weak base drug (pK$$_a = 8) is $$formulated as its hydrochloride salt. What is the main reason for this choice?

Accepted Answer

To increase water solubility in acidic environments

Question 15

How many stereoisomers are possible for a molecule with three chiral centers?

Accepted Answer

8

Question 16

Which of the following best describes enantiomers?

Accepted Answer

Non-superimposable mirror images

Question 17

Which of the following is a geometric (cis/trans) isomerism example?

Accepted Answer

2-butene

Question 18

A patient is prescribed a racemic mixture of a chiral drug. Which statement is TRUE?

Accepted Answer

The mixture contains equal amounts of both enantiomers.

Question 19

Which of the following is a property that differs between diastereomers?

Accepted Answer

Physical properties such as melting point

Question 20

A weak acid drug (pK$$_a = 4) is 99$$% ionized at pH 6. What is the percent unionized at this pH?

Accepted Answer

1%

Acidity and Basicity of Functional Groups & The Henderson-Hasselbalch Equation

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