Question 1

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

Accepted Answer

A substance that donates a proton.

Question 2

Given the reaction: $$\mathrm{NH_3$ + H_2O \rightleftharpoons NH_4$^+ + OH^-}$$, identify the conjugate acid-base pairs.

Accepted Answer

$$\mathrm{NH_3$/NH_4$^+}$$~and~$$\mathrm{H_2O/OH^-}$$

Question 3

Which of the following acids is the strongest based on their $$pK_a$$ values?

Accepted Answer

Hydrochloric acid ($$pK_a = -7)$$

Question 4

A solution contains $$0.1~\mathrm{M}$$ acetic acid ($$CH_3COOH) $$and $$0.1~\mathrm{M}$$ sodium acetate ($$CH_3COONa). $$The $$pK_a of $$acetic acid is $$4.76. $$What is the pH of the solution?

Accepted Answer

$$pH = 4.76$$

Question 5

Which factor most increases the acidity of a molecule?

Accepted Answer

Increasing resonance stabilization of the conjugate base.

Question 6

Which of the following statements about strong acids is correct?

Accepted Answer

Strong acids have weak conjugate bases.

Question 7

Using the Henderson-Hasselbalch equation, calculate the ratio $$\left(\frac{[A^-]}{[HA]}\right)$$ when $$pH = pK_a + 2.$$

Accepted Answer

100

Question 8

Which of the following bases can deprotonate acetylene ($$HC \equiv CH$$)? (Given: $$pK_a of $$acetylene = 25, $$pK_a of $$ammonia = 38, $$pK_a of $$water = 15.7)

Accepted Answer

Sodium amide ($$NaNH_2)$$

Question 9

Which of the following statements about the relationship between $$pH$$ and $$pK_a is $$correct?

Accepted Answer

When $$pH = pK_a$$, $$[A^-] = [HA]$$

Question 10

Which of the following is a Lewis acid but not a Brønsted-Lowry acid?

Accepted Answer

$$BF_3$$

Question 11

Which of the following best explains why $$CF_3CH_2OH is a $$stronger acid than $$CH_3CH_2OH$$?

Accepted Answer

The trifluoromethyl group increases inductive electron withdrawal.

Question 12

Which of the following statements is true regarding the direction of an acid-base equilibrium?

Accepted Answer

The equilibrium favors the side with the weaker acid and base.

Question 13

Which of the following compounds has the most acidic proton?

Accepted Answer

Acetic acid ($$CH_3COOH$$, $$pK_a \approx 4.8)$$

Question 14

Which of the following factors does NOT stabilize the conjugate base of an acid?

Accepted Answer

Decreased electronegativity of the atom bearing the charge

Question 15

Which of the following is the correct expression for the acid dissociation constant ($$K_a) $$for acetic acid ($$CH_3COOH) in $$water?

Accepted Answer

$$K_a = \frac{[CH_3COO^-][H_3O^+]}{[CH_3COOH]}$$

Question 16

Which of the following statements about the effect of atomic size on acid strength is correct?

Accepted Answer

As atomic size increases, acid strength increases.

Question 17

Which of the following is the best explanation for why $$CH_3COO^- is a $$weaker base than $$CH_3CH_2O^-$$?

Accepted Answer

$$CH_3COO^-$$ has resonance stabilization.

Question 18

Which of the following is true for a weak acid in water?

Accepted Answer

Its $$pK_a is $$positive and its equilibrium lies to the left.

Question 19

Which of the following is the correct Lewis structure for the hydronium ion?

Accepted Answer

A central oxygen atom bonded to three hydrogens with a positive charge.

Acid-Base Reactions: Brønsted-Lowry and Lewis Theories, Strength, and Equilibria

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