Question 1

Which of the following statements best explains why HI is a stronger acid than HF, even though fluorine is more electronegative than iodine?

Accepted Answer

HI is a stronger acid because the larger size of iodine allows the negative charge on the conjugate base to be more delocalized and stabilized.

Question 2

Which of the following compounds has the most acidic hydrogen, and why?

1) $$CH_4
2$$) $$NH_3
3$$) $$H_2O
4$$) $$HF$$

Accepted Answer

$$HF$$, because fluorine is the most electronegative element, stabilizing the negative charge on the conjugate base.

Question 3

Which of the following best describes the effect of resonance on acid strength?

Accepted Answer

Resonance stabilizes the conjugate base, making the acid stronger.

Question 4

Given the following pKa values, which compound is the strongest acid?

$$CH_3OH ($$pKa = 15.5), $$CH_3COOH ($$pKa = 4.76), $$NH_3 ($$pKa = 36), $$H_2O ($$pKa = 15.7)

Accepted Answer

$$CH_3COOH$$, because it has the lowest pKa value.

Question 5

Which of the following best explains why carboxylic acids are generally stronger acids than alcohols?

Accepted Answer

The conjugate base of a carboxylic acid is stabilized by resonance, while the conjugate base of an alcohol is not.

Question 6

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

Accepted Answer

$$BF_3$$

Question 7

A solution contains both acetic acid ($$CH_3COOH$$, pKa = 4.76) and formic acid ($$HCOOH$$, pKa = 3.75). Which acid will donate a proton more readily, and why?

Accepted Answer

Formic acid, because it has a lower pKa value.

Question 8

Which of the following factors does NOT increase the acidity of a compound?

Accepted Answer

Decreasing the electronegativity of the atom bonded to the acidic hydrogen.

Question 9

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

Accepted Answer

The equilibrium favors the formation of the weaker acid and weaker base.

Question 10

Which of the following compounds will have the most stable conjugate base?

A) $$CH_3CH_2OH
B$$) $$CH_3COOH
C$$) $$CH_3CH_3
D$$) $$CH_3NH_2$$

Accepted Answer

$$CH_3COOH$$, due to resonance stabilization of the carboxylate anion.

Question 11

Which of the following best explains why the acidity of $$CH_3CH_2OH ($$ethanol) is less than that of $$CH_3COOH ($$acetic acid)?

Accepted Answer

The conjugate base of acetic acid is stabilized by resonance, while the conjugate base of ethanol is not.

Question 12

Which of the following will increase the acidity of a carboxylic acid the most?

Accepted Answer

Adding a fluorine atom to the carbon adjacent to the carboxyl group.

Question 13

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

1) $$HC \equiv CH
2$$) $$H_2C=CH_2$
3) CH_3CH_3$

Accepted Answer

$$HC \equiv CH \u003e H_2C=CH_2$ \u003e CH_3CH_3$$

Question 14

Which of the following best describes the effect of increasing s-character in the hybridization of the atom bonded to the acidic hydrogen?

Accepted Answer

Increasing s-character increases acidity because the negative charge is held closer to the nucleus.

Question 15

Which of the following is the strongest base?

A) $$CH_3O^-
B$$) $$F^-
C$$) $$NH_2$$^-$$
D) CH_3$$COO^-$$

Accepted Answer

$$NH_2$$^-$$, because its conjugate acid (NH_3$) has the highest pKa.

Question 16

A patient is stung by an ant, which injects formic acid ($$pK_a = 3.8) $$into the skin. Which household substance would best neutralize the sting?

Accepted Answer

A weak base such as ammonia ($$NH_3$$, $$pK_a = 9.4$$), because it will react with the acid to form a weaker acid-base pair.

Question 17

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

Accepted Answer

The lower the pKa, the stronger the acid.

Question 18

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

Accepted Answer

$$CH_3COO^- is $$resonance stabilized, making it a weaker base.

Acids and Bases: Central to Understanding Organic Chemistry

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