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 following acids and their approximate $$pK_a$$ values: acetic acid ($$pK_a = 4.76$$), water ($$pK_a = 15.7$$), and ammonia ($$pK_a = 38$$), which is the strongest acid?

Accepted Answer

Acetic acid

Question 3

Which factor most directly increases the acidity of a compound by stabilizing its conjugate base?

Accepted Answer

Increasing resonance delocalization

Question 4

What is the relationship between acid strength and the strength of its conjugate base?

Accepted Answer

Strong acids have weak conjugate bases.

Question 5

Which of the following acids would have the most product-favored equilibrium when reacting with water? Use the following $$pK_a$$ values: $$HCl$$ ($$pK_a = -7$$), $$CH_3COOH$$ ($$pK_a = 4.76$$), $$H_2O$$ ($$pK_a = 15.7$$), $$NH_4$$^+$$ (pK_a = 9.2$).

Accepted Answer

$$HCl$$

Question 6

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

Accepted Answer

The larger size of iodine allows better charge delocalization in the conjugate base.

Question 7

A solution contains acetic acid ($$pK_a = 4.76) $$and is at $$pH = 3.76. $$Which form predominates?

Accepted Answer

The acidic form ($$HA)$$

Question 8

Which of the following is the correct Henderson-Hasselbalch equation?

Accepted Answer

$$pH = pK_a + \log \frac{[A^-]}{[HA]}$$

Question 9

Which of the following functional groups is the most acidic?

Accepted Answer

Carboxylic acid

Question 10

Which of the following statements about resonance and acidity is correct?

Accepted Answer

Resonance stabilizes the conjugate base, increasing acidity.

Question 11

If the $$pK_a of an $$acid is 5 and the $$pH of $$the solution is 7, what is the ratio $$\frac{[A^-]}{[HA]}$$?

Accepted Answer

100

Question 12

Which of the following best describes the effect of an electron-withdrawing substituent on the acidity of a carboxylic acid?

Accepted Answer

It decreases the $$pK_a$$ and increases acidity.

Question 13

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

Accepted Answer

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

Question 14

Which of the following is NOT a factor that increases acid strength?

Accepted Answer

Decreased atomic size

Question 15

Which of the following best describes a Lewis acid?

Accepted Answer

An electron pair acceptor

Question 16

Which of the following statements is true regarding the effect of hybridization on acidity?

Accepted Answer

An sp-hybridized atom is more acidic due to higher s-character.

Question 17

A student mixes $$NH_3$$ ($$pK_a = 38) $$with $$H_2O$$ ($$pK_a = 15.7). $$Which direction does the equilibrium favor?

Accepted Answer

Reactants

Question 18

Which of the following is the correct formula for calculating $$pK_a$$ from $$K_a$$?

Accepted Answer

$$pK_a = -\log K_a$$

Question 19

Which of the following best explains why carboxylic acids are more acidic than alcohols?

Accepted Answer

Carboxylic acids have more resonance stabilization in their conjugate base.

Question 20

Which of the following is the correct interpretation when $$pH = pK_a$$ for a weak acid?

Accepted Answer

The concentrations of $$HA$$ and $$A^-$$ are equal.

Acids and Bases: Central to Understanding Organic Chemistry

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