Question 1

Which of the following best describes a Lewis acid according to the definitions provided in the study materials?

Accepted Answer

An electron pair acceptor.

Question 2

Given the following acids, which one would you expect to have the lowest $$pK_a$$ value based on electronegativity trends?

Accepted Answer

$$\mathrm{HF}$$

Question 3

Which of the following statements about acid-base equilibria is correct?

Accepted Answer

Acid-base reactions favor the formation of the weaker acid and weaker base.

Question 4

Which factor does NOT contribute to the stability of a conjugate base?

Accepted Answer

Molecular weight

Question 5

Consider the following equilibrium:

$$\mathrm{CH_3CH_2OH + NH_2$^- \rightleftharpoons CH_3CH_2O^- + NH_3$}$$

Given $$pK_a$$ values: $$\mathrm{CH_3CH_2OH}$$ ($$pK_a = 15.9$$), $$\mathrm{NH_3$}$$ ($$pK_a = 38). $$Which direction is favored?

Accepted Answer

To the left, forming $$\mathrm{CH_3CH_2OH}$$ and $$\mathrm{NH_2$^-}$$

Question 6

Which of the following acids is expected to have the most stable conjugate base due to resonance stabilization?

Accepted Answer

Acetic acid ($$\mathrm{CH_3COOH})$$

Question 7

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

Accepted Answer

A larger $$K_a$$ corresponds to a smaller $$pK_a.$$

Question 8

Which of the following best explains why acidity increases down a group in the periodic table (e.g., $$\mathrm{HF} \u003c \mathrm{HCl} \u003c \mathrm{HBr} \u003c \mathrm{HI}$$)?

Accepted Answer

The size of the atom bonded to hydrogen increases, stabilizing the conjugate base.

Question 9

Which of the following is the correct $$pK_a$$ value for water, based on the materials provided?

Accepted Answer

$$15.7$$

Question 10

Which of the following is the strongest base among the following species, based on periodic trends?

Accepted Answer

$$\mathrm{NH_2$^-}$$

Question 11

Which of the following statements about conjugate acids and bases is correct?

Accepted Answer

A conjugate base is formed when an acid donates a proton.

Question 12

Which of the following is the correct expression for the acid dissociation constant $$K_a$$ for a generic acid $$HA in $$water?

Accepted Answer

$$K_a = \dfrac{[H_3O^+][A^-]}{[HA]}$$

Question 13

Which of the following organic compounds is expected to be the weakest acid?

Accepted Answer

Methane ($$\mathrm{CH_4$})$$

Question 14

Which of the following best explains why acetic acid ($$\mathrm{CH_3COOH}) is a $$stronger acid than ethanol ($$\mathrm{CH_3CH_2OH}$$)?

Accepted Answer

The conjugate base of acetic acid is stabilized by resonance.

Question 15

Which of the following is NOT a correct statement about $$pK_a$$ values?

Accepted Answer

The smaller the $$pK_a$$, the weaker the acid.

Question 16

Which of the following is the correct order of acidity for the following compounds?

$$\mathrm{CH_4$}$$, $$\mathrm{NH_3$}$$, $$\mathrm{H_2O}$$, $$\mathrm{HF}$$

Accepted Answer

$$\mathrm{CH_4$} \u003c \mathrm{NH_3$} \u003c \mathrm{H_2O} \u003c \mathrm{HF}$$

Question 17

Which of the following is a correct statement about the relationship between acid strength and conjugate base strength?

Accepted Answer

The stronger the acid, the weaker its conjugate base.

Question 18

Which of the following factors would most likely increase the acidity of a molecule?

Accepted Answer

Increasing resonance stabilization of the conjugate base.

Question 19

Which of the following best describes why $$\mathrm{HBr} is a $$stronger acid than $$\mathrm{HF}$$?

Accepted Answer

$$\mathrm{Br^-} is $$larger and can better stabilize the negative charge.

Acid-Base Chemistry in Organic Molecules: Fundamentals and Predictive Principles

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