Q: Given that the $$K_w ($$water dissociation constant) at 25°C is $$1 \times 10$$^{-14}$$, what is the concentration of $$[OH^-]$$ in a solution where $$[H^+] = 1 \times $$10^{-4} M$$?

$$[OH^-] = 1 \times 10$$^{-10}$$ M

Question 1

Which of the following best describes the role of water as a nucleophile in biochemical reactions?

Accepted Answer

Water donates a pair of unshared electrons from its oxygen atom to electrophilic centers.

Question 2

Given that the $$K_w ($$water dissociation constant) at 25°C is $$1 	imes 10$$^{-14}$$, what is the concentration of $$[OH^-]$$ in a solution where $$[H^+] = 1 	imes $$10^{-4} M$$?

Accepted Answer

$$[OH^-] = 1 	imes 10$$^{-10}$$ M

Question 3

A solution has a $$[H^+] of$$ $$1 	imes 10$$^{-3}$$ M. What is the pH of this solution?

Accepted Answer

pH = 3

Question 4

Which of the following statements about strong acids and bases is CORRECT?

Accepted Answer

Strong acids and bases completely dissociate in water.

Question 5

Calculate the pH of a 0.2 M acetic acid solution, given that $$K_a$$ for acetic acid is $$1.76 	imes 10$$^{-5}$$.

Accepted Answer

pH = 2.60

Question 6

Which of the following best explains why buffers are important in biological systems?

Accepted Answer

Buffers maintain a constant pH by neutralizing added acids or bases.

Question 7

A buffer is prepared by mixing equal concentrations of acetic acid ($$pK_a = 4.76) $$and sodium acetate. What is the pH of the buffer?

Accepted Answer

pH = 4.76

Question 8

Which equation correctly represents the Henderson-Hasselbalch equation?

Accepted Answer

$$pH = pK_a + \log \frac{[A^-]}{[HA]}$$

Question 9

If you want to prepare a buffer with a pH of 7.2, which of the following buffer systems would be most appropriate?

Accepted Answer

Phosphate ($$pK_{a2} = 7.2)$$

Question 10

A solution contains 0.1 M acetic acid and 0.2 M sodium acetate. What is the pH of the solution? ($$pK_a of $$acetic acid = 4.76)

Accepted Answer

pH = 5.06

Question 11

Which of the following best describes the effect of adding a small amount of strong acid to a well-buffered solution?

Accepted Answer

The pH will change only slightly.

Question 12

Which of the following is TRUE regarding the relationship between $$K_a$$ and $$pK_a$$?

Accepted Answer

$$pK_a = -\log K_a$$

Question 13

A buffer is most effective when:

Accepted Answer

The concentrations of weak acid and its conjugate base are equal.

Question 14

Which of the following statements about polyprotic acids is CORRECT?

Accepted Answer

Each ionization step of a polyprotic acid has a different $$pK_a$$ value.

Question 15

Which of the following is the correct calculation for the ratio $$\frac{[A^-]}{[HA]}$$ needed to prepare a buffer at pH 6.8 using a weak acid with $$pK_a = 6.2$$?

Accepted Answer

$$\frac{[A^-]}{[HA]} = 10$$^{0.6}$$

Question 16

A laboratory buffer is needed at pH 7.0. Which of the following would be the LEAST suitable buffer system?

Accepted Answer

Acetic acid/acetate ($$pK_a = 4.8)$$

Question 17

Which of the following best explains why pure water is considered unbuffered?

Accepted Answer

The concentration of $$H^+$$ and $$OH^- in $$water is too low to resist pH changes.

Question 18

If the pH of blood drops below 7.35, which of the following conditions may result?

Accepted Answer

Acidosis

Question 19

Which of the following is a major buffer system in the blood?

Accepted Answer

Bicarbonate buffer

Question 20

Amino acids can act as buffers because:

Accepted Answer

They contain both an amino group and a carboxyl group, each with its own $$pK_a.$$

Ionization of Water and Acid-Base Chemistry

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