Q: Which of the following equations correctly relates $$K_a$$ and $$K_b$$ for a conjugate acid-base pair at $$25^\circ\mathrm{C}$$?

$$K_a \times K_b = K_w = 1.0 \times 10$$^{-14}$$

Question 1

Which of the following statements best describes a Brønsted–Lowry acid?

Accepted Answer

A substance that donates a proton (H+) to another species.

Question 2

Which pair below represents a conjugate acid-base pair?

Accepted Answer

$$\mathrm{NH_3$}$$~and~$$\mathrm{NH_4$^+}$$

Question 3

A solution has $$[\mathrm{H_3O^+}] = 1.0 	imes 10$$^{-5}$$~\mathrm{M}. $$What is the pH of this solution?

Accepted Answer

$$\mathrm{pH} = 5.0$$

Question 4

Which of the following statements about strong and weak acids is correct?

Accepted Answer

A strong acid donates all of its protons to water, while a weak acid only partially donates protons.

Question 5

Given $$\mathrm{pH} + \mathrm{pOH} = 14 at$$ $$25^\circ\mathrm{C}$$, what is the pOH of a solution with $$\mathrm{pH} = 3.5$$?

Accepted Answer

$$\mathrm{pOH} = 10.5$$

Question 6

Which of the following best explains why the conjugate base of a strong acid is weak?

Accepted Answer

Because the strong acid completely dissociates, leaving its conjugate base with little tendency to accept protons.

Question 7

A 0.10 M solution of a weak acid, HA, has a pH of 3.0. What is the value of $$K_a$$ for this acid? (Assume $$[\mathrm{H_3O^+}] = [\mathrm{A^-}]$$ and $$[\mathrm{HA}]_{eq} \approx 0.10~\mathrm{M})$$

Accepted Answer

$$K_a = 1.0 	imes 10$$^{-5}$$

Question 8

Which of the following equations correctly relates $$K_a$$ and $$K_b$$ for a conjugate acid-base pair at $$25^\circ\mathrm{C}$$?

Accepted Answer

$$K_a 	imes K_b = K_w = 1.0 	imes 10$$^{-14}$$

Question 9

Which of the following statements about buffer solutions is correct?

Accepted Answer

A buffer solution resists changes in pH when small amounts of acid or base are added.

Question 10

A buffer is prepared by mixing 0.20 mol of acetic acid ($$\mathrm{CH_3COOH}) $$and 0.20 mol of sodium acetate ($$\mathrm{CH_3COONa}) in $$enough water to make 1.0 L of solution. If the $$pK_a of $$acetic acid is 4.74, what is the pH of the buffer?

Accepted Answer

$$\mathrm{pH} = 4.74$$

Question 11

Which of the following best describes the Henderson–Hasselbalch equation?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log \left( \dfrac{[\mathrm{A^-}]}{[\mathrm{HA}]} \right)$$

Question 12

A buffer solution is most effective when:

Accepted Answer

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

Question 13

If the $$pK_a of a $$weak acid is 5.0, over what approximate pH range will a buffer made from this acid and its conjugate base be effective?

Accepted Answer

$$4.0~	ext{to}~6.0$$

Question 14

A 1.0 M solution of acetic acid ($$K_a = 1.8 	imes 10$$^{-5}$$) is prepared. What is the approximate pH of this solution? (Assume x$$ \ll 1.0$$ and x^2$ = K_a 	imes 1.0)$$

Accepted Answer

$$\mathrm{pH} \approx 2.74$$

Question 15

Which of the following changes will NOT significantly affect the pH of a buffer solution?

Accepted Answer

Adding a small amount of strong acid.

Question 16

A weak base, B, has a $$K_b of$$ $$1.0 	imes 10$$^{-5}$$. What is the pK_b$?

Accepted Answer

$$pK_b = 5.0$$

Question 17

Which of the following is true for pure water at $$25^\circ\mathrm{C}$$?

Accepted Answer

$$[\mathrm{H_3O^+}] = [\mathrm{OH^-}]$$

Question 18

A buffer solution is made by mixing 0.10 M formic acid ($$pK_a = 3.75) $$and 0.30 M sodium formate. What is the pH of the buffer?

Accepted Answer

$$\mathrm{pH} = 4.23$$

Question 19

Which of the following best describes why buffer solutions are important in biological systems?

Accepted Answer

They maintain a relatively constant pH, which is crucial for enzyme activity and metabolic processes.

Acid-Base Equilibrium: Weak Acids, Bases, and Buffer Solutions

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