Q: If the $$K_b of $$ammonia is $$1.8 \times 10$$^{-5}$$ at 25°C, what is the pK_b$?

$$pK_b = -\log(1.8 \times 10$$^{-5}$$) = 4.74$$

Question 1

Which of the following statements best explains why most pharmaceutical drugs are formulated as salts?

Accepted Answer

Salt forms improve the drug's solubility and stability, making them easier to formulate and absorb.

Question 2

A buffer solution is prepared by mixing 25 mL of 0.2 M benzoic acid and 45 mL of 0.1 M sodium benzoate. The pKa of benzoic acid is 4.22. What is the pH of the solution?

Accepted Answer

pH = 4.22 + $$\log\left(\frac{5}{4.5}\right) = 4.26$$

Question 3

Which of the following is NOT a factor that can cause pH drift in a pharmaceutical solution?

Accepted Answer

Increasing the temperature of the solution to 25°C

Question 4

Which buffer system would be most appropriate for a drug that is unstable at acidic pH and needs to be formulated near neutral pH?

Accepted Answer

Phosphate buffer (pH near 7)

Question 5

A solution contains 25 mL of 1 M acetic acid and 40 mL of 1 M sodium acetate. The pKa of acetic acid is 4.76. What is the pH of the solution?

Accepted Answer

pH = 4.76 + $$\log\left(\frac{40}{25}\right) = 5.02$$

Question 6

Which of the following best describes an amphoteric substance?

Accepted Answer

A substance that can act as either an acid or a base depending on the environment

Question 7

What is the physiological pH range of human blood?

Accepted Answer

7.35 - 7.45

Question 8

Which of the following equations correctly relates the acid dissociation constant ($$K_a) to $$its $$pK_a$$?

Accepted Answer

$$pK_a = -\log(K_a)$$

Question 9

A pharmacist is preparing a buffer for a drug that is sensitive to pH changes. Which property of the buffer is most important to consider?

Accepted Answer

The buffer's capacity to resist changes in pH

Question 10

Which of the following is a common misconception about weak acids?

Accepted Answer

Weak acids are strong electrolytes.

Question 11

If the $$K_b of $$ammonia is $$1.8 	imes 10$$^{-5}$$ at 25°C, what is the pK_b$?

Accepted Answer

$$pK_b = -\log(1.8 	imes 10$$^{-5}$$) = 4.74$$

Question 12

Which of the following would most likely cause an acidic shift in the pH of a solution over time?

Accepted Answer

Absorption of CO$$_2$$ from the atmosphere

Question 13

Why is it important for a pharmacist to know the pH of maximum stability for a drug before preparing a solution?

Accepted Answer

To maximize the drug's stability and efficacy in solution

Question 14

Which of the following buffer systems should never be injected due to safety concerns?

Accepted Answer

Sodium borate-boric acid buffer

Question 15

A patient is experiencing metabolic acidosis. Which of the following best describes this condition?

Accepted Answer

There is too much acid in the blood, lowering the pH.

Question 16

Which of the following is true regarding the relationship between $$pK_a$$ and acid strength?

Accepted Answer

A lower $$pK_a$$ value indicates a stronger acid.

Question 17

Which of the following is the correct definition of a base according to the Bronsted-Lowry theory?

Accepted Answer

A substance that accepts a proton (H$$^+)$$

Question 18

Which of the following is a real-world consequence of a drug formulation with a pH outside the acceptable range for its route of administration?

Accepted Answer

The drug may cause irritation or damage to tissues.

Question 19

Which of the following is the neutral pH at room temperature (25°C)?

Accepted Answer

pH 7

Question 20

Which of the following statements about buffer solutions is correct?

Accepted Answer

Buffer solutions can resist changes in pH when small amounts of strong acid or base are added.

Acid-Base Chemistry, pH, and Buffer Systems in Physiology and Pharmacy

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