Q: Which of the following is the correct form of the Henderson-Hasselbalch equation?

$$pH = pK_a + \log \left( \frac{[\text{conjugate base}]}{[\text{acid}]} \right)$$

Q: Which of the following is the correct formal charge calculation for the central atom in $$\mathrm{CH_3NH_3^+}$$?

$$FC_N = 5 - (4 + 1/2 \times 4) = +1$$

Question 1

Which of the following statements best explains why the equilibrium in an acid-base reaction favors the formation of the weaker acid?

Accepted Answer

The weaker acid is less likely to donate protons, so the equilibrium favors its formation to minimize free protons in solution.

Question 2

Given the following reaction: $$\mathrm{CH_3COOH} + \mathrm{OH^-} \rightarrow \mathrm{CH_3COO^-} + \mathrm{H_2O}$$, and the pKa of acetic acid is 4.76, while the pKa of water is 15.7. Which direction does the equilibrium favor?

Accepted Answer

The equilibrium favors the products because water is a weaker acid than acetic acid.

Question 3

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

Accepted Answer

$$pH = pK_a + \log \left( \frac{[	ext{conjugate base}]}{[	ext{acid}]} ight)$$

Question 4

A solution contains equal concentrations of acetic acid and its conjugate base. If the pKa of acetic acid is 4.76, what is the pH of the solution?

Accepted Answer

$$pH = 4.76$$

Question 5

If the pH of a buffer solution made from aspirin (pKa = 3.0) is 2.0, what is the ratio $$\frac{[	ext{conjugate base}]}{[	ext{acid}]}$$?

Accepted Answer

$$0.1$$

Question 6

Which of the following species is the strongest base according to the relative strengths shown in the materials?

Accepted Answer

$$\mathrm{R_3N} ($$trialkylamine)$

Question 7

In the reaction $$\mathrm{CH_3CH_2O^-} + \mathrm{CH_3NH_3^+} \rightarrow \mathrm{CH_3CH_2OH} + \mathrm{CH_3NH_2}$$, the pKa of $$\mathrm{CH_3CH_2OH} is 16 $$and the pKa of $$\mathrm{CH_3NH_3^+} is 10.7. $$Which direction does the equilibrium favor?

Accepted Answer

The equilibrium favors the products because $$\mathrm{CH_3CH_2OH} is a $$weaker acid.

Question 8

Which of the following best describes a Lewis acid?

Accepted Answer

A species that accepts an electron pair.

Question 9

What is the formal charge on the nitrogen atom in $$\mathrm{CH_3NH_3^+}$$?

Accepted Answer

$$+1$$

Question 10

A buffer is prepared using acetic acid ($$pK_a = 4.76) $$and sodium acetate. If the ratio $$\frac{[	ext{conjugate base}]}{[	ext{acid}]} = 10$$, what is the pH of the buffer?

Accepted Answer

$$pH = 5.76$$

Question 11

Which of the following statements is true regarding the relationship between acid strength and conjugate base strength?

Accepted Answer

A strong acid has a weak conjugate base.

Question 12

If the pKa of a carboxylic acid is 3.49 and the pH of the solution is 1.0, what is the ratio $$\frac{[\mathrm{RCOO^-}]}{[\mathrm{RCOOH}]}$$?

Accepted Answer

$$0.00324$$

Question 13

Which of the following best explains why $$\mathrm{$$AlCl_3$$}$$ acts as a Lewis acid in the reaction with $$\mathrm{CH_3O^-}$$?

Accepted Answer

$$\mathrm{$$AlCl_3$$}$$ accepts an electron pair from $$\mathrm{CH_3O^-}.$$

Question 14

Aspirin has a pKa of 3.0. At pH 8, what is the predominant form of aspirin in solution?

Accepted Answer

Mostly in the deprotonated (ionic) form.

Question 15

Which of the following is the correct formal charge calculation for the central atom in $$\mathrm{CH_3NH_3^+}$$?

Accepted Answer

$$FC_N = 5 - (4 + 1/2 	imes 4) = +1$$

Question 16

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

Accepted Answer

The equilibrium always favors the side with the weaker acid.

Question 17

Which of the following is the correct order of acid strength (from strongest to weakest) based on the materials?

Accepted Answer

$$\mathrm{H-X} \u003e \mathrm{H_3O^+} \u003e \mathrm{ROH} \u003e \mathrm{H_2O} \u003e \mathrm{$$RNH_3$$^+}$$

Question 18

Acetaminophen has a pKa of 9.5. At physiological pH (7.4), what is the predominant form of acetaminophen?

Accepted Answer

Mostly in the protonated (neutral) form.

Question 19

Which of the following best describes the effect of increasing the concentration of the conjugate base in a buffer solution?

Accepted Answer

The pH of the solution increases.

Question 20

In the context of Le Chatelier's Principle, what happens if you add more acid to a buffer system?

Accepted Answer

The buffer will convert some of the added acid to its conjugate base, minimizing the pH change.

Acid-Base Chemistry in Organic Molecules: Strengths, Equilibria, and Lewis Theory

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