Q: Which of the following equations represents the Henderson-Hasselbalch equation for a buffer solution?

$$pH = pK_a + \log \left( \frac{[\text{Base}]}{[\text{Acid}]} \right)$$

Q: What is the main reason the pH of a buffer solution does not change significantly when diluted with water?

The $$[\text{base}]/[\text{acid}]$$ ratio remains constant.

Question 1

Which of the following best explains why the addition of sodium acetate to a solution of acetic acid decreases the concentration of $$\mathrm{H_3O^+} in $$the solution?

Accepted Answer

The added acetate ions shift the acid-dissociation equilibrium of acetic acid to the left, reducing $$\mathrm{H_3O^+}$$ concentration.

Question 2

A buffer solution is prepared by mixing 0.10 mol of acetic acid and 0.10 mol of sodium acetate in 1.00 L of water. What is the pH of this buffer if $$K_a$$ for acetic acid is $$1.8 	imes 10$$^{-5}$$?

Accepted Answer

$$pH = 4.74$$

Question 3

Which of the following statements about buffer solutions is correct?

Accepted Answer

A buffer solution resists drastic changes in pH when small amounts of acid or base are added.

Question 4

What happens to the ratio of weak acid to conjugate base in a buffer solution when a small amount of $$\mathrm{OH^-} is $$added?

Accepted Answer

The amount of weak acid decreases and the amount of conjugate base increases.

Question 5

A titration curve for the titration of 40.0 mL of 0.100 M HCl with 0.100 M NaOH shows a sharp increase in pH at the equivalence point. What is the pH at the equivalence point?

Accepted Answer

$$pH = 7.00$$

Question 6

During the titration of a weak acid with a strong base, which indicator would be most appropriate to detect the equivalence point if the equivalence point occurs at $$pH = 8.72$$?

Accepted Answer

Phenolphthalein

Question 7

Which of the following best describes the effect of adding $$\mathrm{H_3O^+} to a $$buffer solution containing a weak acid and its conjugate base?

Accepted Answer

The added $$\mathrm{H_3O^+} is $$neutralized by the conjugate base, forming more weak acid.

Question 8

If 40.0 mL of 0.100 M HCl is titrated with 0.100 M NaOH, how many mL of NaOH are required to reach the equivalence point?

Accepted Answer

40.0 mL

Question 9

Which of the following is true about the pH at the equivalence point in the titration of a strong acid with a strong base?

Accepted Answer

The pH is exactly 7.

Question 10

In a titration of 40.0 mL of 0.100 M acetic acid with 0.100 M NaOH, what is the major species present at the equivalence point?

Accepted Answer

Sodium acetate

Question 11

Which of the following best explains why the pH at the equivalence point in the titration of a weak acid with a strong base is greater than 7?

Accepted Answer

The conjugate base of the weak acid hydrolyzes to produce $$\mathrm{OH^-}$$ ions.

Question 12

A buffer solution is most effective when:

Accepted Answer

The concentrations of weak acid and conjugate base are equal and relatively high.

Question 13

Which of the following equations represents the Henderson-Hasselbalch equation for a buffer solution?

Accepted Answer

$$pH = pK_a + \log \left( \frac{[	ext{Base}]}{[	ext{Acid}]} ight)$$

Question 14

What is the main reason the pH of a buffer solution does not change significantly when diluted with water?

Accepted Answer

The $$[	ext{base}]/[	ext{acid}]$$ ratio remains constant.

Question 15

Which of the following best describes the change in pH when a small amount of strong acid is added to a buffer solution?

Accepted Answer

The pH decreases only slightly.

Question 16

In the titration of a strong acid with a strong base, what is the main species present in the solution after the equivalence point?

Accepted Answer

Excess strong base

Question 17

Which of the following is a correct net ionic equation for the neutralization of acetic acid with sodium hydroxide?

Accepted Answer

$$\mathrm{CH_3CO_2H(aq) + OH^-(aq) \rightarrow CH_3CO_2^-(aq) + H_2O(l)}$$

Question 18

Which of the following best describes the buffer region on a titration curve?

Accepted Answer

The region where the pH changes only slightly with the addition of titrant.

Chapter 17: Applications of Aqueous Equilibria – Buffers, Titrations, and Solubility

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