$$\text{BF}_3$$ acts as a Lewis acid by accepting an electron pair from diethyl ether.

Question 1

Which of the following statements best describes the use of curved arrows in organic reaction mechanisms?

Accepted Answer

A full-headed curved arrow shows the movement of a pair of electrons from the source to the sink.

Question 2

In the dissociation of a generic acid $$HA in $$water, which of the following equations correctly represents the acid dissociation constant $$K_a$$?

Accepted Answer

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

Question 3

Which of the following factors does NOT increase the acidity of a proton in an organic molecule?

Accepted Answer

Decreasing the size of the atom bonded to the proton.

Question 4

Which of the following best explains why trifluoroethanol ($$CF_3CH_2OH) is a $$much stronger acid than ethanol ($$CH_3CH_2OH$$)?

Accepted Answer

The presence of fluorine atoms increases the inductive effect, stabilizing the conjugate base.

Question 5

Given the following acids and their $$pK_a$$ values: acetic acid ($$pK_a = 4.75) $$and ethanol ($$pK_a = 16$$), which statement is correct?

Accepted Answer

Acetic acid is a stronger acid because its conjugate base is stabilized by resonance.

Question 6

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

Accepted Answer

The equilibrium favors the side with the weaker acid (higher $$pK_a).$$

Question 7

Which of the following is a correct application of the Brønsted-Lowry definition of acids and bases?

Accepted Answer

A Brønsted-Lowry acid is a species that donates a proton to a base.

Question 8

Which of the following best describes the role of $$	ext{BF}_3 in $$the reaction with diethyl ether ($$	ext{OEt}_2$$)?

Accepted Answer

$$	ext{BF}_3$$ acts as a Lewis acid by accepting an electron pair from diethyl ether.

Question 9

Which of the following statements about resonance stabilization is correct?

Accepted Answer

Resonance stabilization of the conjugate base increases the acidity of the acid.

Question 10

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

Accepted Answer

$$pK_a = -\log_{10} K_a$$

Question 11

Consider the following acid-base reaction:

$$CH_3CO_2H + NH_3$ \rightleftharpoons CH_3CO_2^- + NH_4$^+$$

Given $$pK_a(CH_3CO_2H) = 4.75$$ and $$pK_a(NH_4$^+) = 9.25$$, which direction is favored at equilibrium?

Accepted Answer

The reaction favors the formation of $$CH_3CO_2^-$$ and $$NH_4$$^+$$.

Question 12

Which of the following best explains why hydroiodic acid ($$HI) is a $$stronger acid than hydrofluoric acid ($$HF$$)?

Accepted Answer

The larger size of iodine leads to a weaker H–I bond, making it easier to lose a proton.

Question 13

Which of the following is NOT a Lewis acid?

Accepted Answer

$$NH_3$$

Question 14

Which of the following statements about the relationship between Brønsted-Lowry and Lewis acid-base theories is correct?

Accepted Answer

All Brønsted-Lowry acids are Lewis acids.

Question 15

Which of the following best describes the effect of increasing the number of electronegative atoms near a proton in an organic molecule?

Accepted Answer

It increases the acidity of the proton due to inductive effects.

Question 16

Which of the following curved arrow conventions is correct for showing the movement of electrons in a proton transfer reaction?

Accepted Answer

The arrow starts at the base and ends at the proton being transferred.

Question 17

Which of the following is the best explanation for why the conjugate base of acetic acid is more stable than that of ethanol?

Accepted Answer

The conjugate base of acetic acid is stabilized by resonance delocalization.

Question 18

Which of the following is a correct statement about the movement of electrons in a multiple bond during a reaction?

Accepted Answer

A curved arrow starting at a multiple bond implies movement of only two electrons (the $$\pi$$ electrons), while the $$\sigma$$ bond remains intact.

Question 19

Which of the following is the correct definition of a Lewis base?

Accepted Answer

A species that donates an electron pair.

Acids, Bases, and Electron Flow in Organic Chemistry

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