Question 1

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

Accepted Answer

A substance that donates a proton (H+).

Question 2

Given the reaction $$\mathrm{HCl} + \mathrm{H_2O} \rightarrow \mathrm{Cl^-} + \mathrm{H_3O^+}$$, identify the conjugate acid and conjugate base.

Accepted Answer

Conjugate acid: H3O+; Conjugate base: Cl-

Question 3

Which of the following factors most strongly increases the acidity of a molecule according to the CARDIN-al rule?

Accepted Answer

The presence of a positive charge on the atom bearing the acidic proton.

Question 4

Which of the following statements about reaction coordinate diagrams is correct?

Accepted Answer

The overall free energy change ($$\Delta G^\circ) is $$always negative for spontaneous reactions.

Question 5

Which of the following acids is the strongest based on periodic trends?

Accepted Answer

$$\mathrm{HI}$$

Question 6

What is the effect of resonance delocalization on the stability of a conjugate base?

Accepted Answer

It increases the stability by spreading the negative charge over multiple atoms.

Question 7

Which of the following statements about pKa and acid strength is correct?

Accepted Answer

A lower pKa value means a stronger acid.

Question 8

Consider the following reaction: $$\mathrm{CH_3CH_2OH} + \mathrm{Na^+CN^-} \rightleftharpoons \mathrm{CH_3CH_2O^-Na^+} + \mathrm{HCN}. $$Given $$pK_a(\mathrm{CH_3CH_2OH}) = 16.0$$ and $$pK_a(\mathrm{HCN}) = 9.3$$, which side is favored?

Accepted Answer

Reactants are favored because HCN is a stronger acid than ethanol.

Question 9

Which of the following best explains why phenol ($$pK_a = 10) is a $$stronger acid than ethanol ($$pK_a = 16$$)?

Accepted Answer

Phenol's conjugate base is stabilized by resonance.

Question 10

Which of the following is the correct relationship between $$\Delta G^\circ$$ and the equilibrium constant $$K_{eq}$$?

Accepted Answer

$$\Delta G^\circ = -RT \ln K_{eq}$$

Question 11

Which of the following functional groups is most likely to act as a base in an organic molecule?

Accepted Answer

An amine group (–NH2)

Question 12

Which of the following statements about the effect of electron-withdrawing groups (EWGs) on acidity is correct?

Accepted Answer

EWGs increase acidity by stabilizing the conjugate base.

Question 13

At physiological pH ($$\sim 7.4$$), which group on fexofenadine (Allegra®) is most likely to be deprotonated?

Accepted Answer

The carboxylic acid group ($$pK_a \sim 5)$$

Question 14

Which of the following best describes a zwitterion?

Accepted Answer

A molecule with both positive and negative formal charges but a net charge of zero.

Question 15

Which of the following bases is the strongest according to the table of conjugate bases: ethoxide ion ($$\mathrm{CH_3CH_2O^-}$$), hydroxide ion ($$\mathrm{HO^-}$$), cyanide ion ($$\mathrm{CN^-}$$), or chloride ion ($$\mathrm{Cl^-}$$)?

Accepted Answer

Ethoxide ion ($$\mathrm{CH_3CH_2O^-})$$

Question 16

Which of the following statements about the effect of hybridization on acidity is correct?

Accepted Answer

An sp-hybridized carbon is more acidic than an sp3-hybridized carbon.

Question 17

Which of the following is the best qualitative predictor of acid strength for the series HF, HCl, HBr, HI?

Accepted Answer

Size of the halogen atom.

Question 18

Which of the following is true about the direction of proton transfer reactions?

Accepted Answer

Proton transfer reactions favor the side with the weaker acid.

Question 19

If the pKa difference between the acid and conjugate acid in a reaction is 10, what is the approximate equilibrium constant ($$K_{eq}) $$for the reaction?

Accepted Answer

$$K_{eq} = 10$$^{10}$$

Chapter 6: Proton Transfer Reactions and Acid-Base Chemistry

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