Question 1

Which of the following best describes the function of a buffer solution?

Accepted Answer

A buffer solution maintains a constant pH by neutralizing added acids or bases through the presence of a weak acid and its conjugate base.

Question 2

Given a buffer solution containing 0.50 M CH$$_3$$COOH and 0.50 M CH$$_3$$COO$$^-$$, and $$K_a$$ for CH$$_3$$COOH is $$1.8 	imes 10$$^{-5}$$, what is the pH of the solution? Use the Henderson-Hasselbalch equation.

Accepted Answer

$$\mathrm{pH} = 4.74$$

Question 3

If 0.020 mol of solid NaOH is added to 1.0 L of the buffer solution in the previous question, what will be the new pH? (Assume negligible volume change.)

Accepted Answer

$$\mathrm{pH} = 4.89$$

Question 4

Which chemical equation best represents the reaction that occurs when H$$_3O$^+ is $$added to an acetic acid/acetate buffer?

Accepted Answer

$$\mathrm{CH_3COO^-} + \mathrm{H_3O^+} \rightarrow \mathrm{CH_3COOH} + \mathrm{H_2O}$$

Question 5

Refer to the first image. What does the equal size of the CH$$_3$$COO$$^-$$ and CH$$_3$$COOH regions represent in a buffer solution?

Accepted Answer

The concentrations of the weak acid and its conjugate base are equal.

Question 6

A buffer is prepared by mixing 1.5 L of 0.20 M NaHCO$$_3$$ with Na$$_2CO$_3 to $$achieve a pH of 10.00. If $$K_a$$ for HCO$$_3^- is$$ $$4.7 	imes 10$$^{-11}$$, which equation would you use to determine the required grams of Na_2$CO_3$?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log \left( \frac{[\mathrm{CO}_3$$^{2-}$$]}{[\mathrm{HCO}_3^-]} \right)$$

Question 7

During the titration of a weak acid with a strong base, what is true about the solution at the half-equivalence point?

Accepted Answer

The pH equals the p$$K_a of $$the weak acid.

Question 8

Refer to the second image. What does the increase in the CH$$_3$$COOH region represent after addition of H$$_3O$^+ to $$the buffer?

Accepted Answer

The added H$$_3O$^+$$ reacts with CH$$_3$$COO$$^- to $$form more CH$$_3$$COOH.

Question 9

Refer to the third image. What does the increase in the CH$$_3$$COO$$^-$$ region represent after addition of OH$$^- to $$the buffer?

Accepted Answer

The added OH$$^-$$ reacts with CH$$_3$$COOH to form more CH$$_3$$COO$$^-.$$

Question 10

Which of the following best explains why buffer capacity increases as the concentrations of the buffer components increase?

Accepted Answer

Higher concentrations of acid and base allow the buffer to neutralize more added acid or base before a significant pH change occurs.

Question 11

A buffer is made by mixing 0.500 M HNO$$_2$$ and 0.500 M NaNO$$_2. $$What volume ratio of these solutions is needed to prepare 1.00 L of buffer at pH 3.51? ($$K_a$$ for HNO$$_2$$ = $$4.00 	imes 10$$^{-4}$$)

Accepted Answer

Equal volumes of HNO$$_2$$ and NaNO$$_2$$ are needed.

Question 12

During the titration of 40.00 mL of 0.1000 M HPr with 0.1000 M NaOH (see the fourth image), what is the approximate pH at the equivalence point?

Accepted Answer

$$\mathrm{pH} \approx 9$$

Question 13

Which of the following equations correctly relates $$K_w$$, $$K_a$$, and $$K_b$$ for a conjugate acid-base pair at 25°C?

Accepted Answer

$$K_w = K_a K_b$$

Question 14

If you want to prepare a buffer with a pH equal to the p$$K_a of $$the acid, what ratio of conjugate base to acid should you use?

Accepted Answer

1:1

Question 15

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

Accepted Answer

The pH decreases slightly because the added acid is neutralized by the conjugate base.

Question 16

A buffer solution is made by dissolving sodium acetate in acetic acid. Which of the following best explains why this buffer resists changes in pH when small amounts of HCl are added?

Accepted Answer

The acetate ion reacts with H$$^+$$ from HCl to form acetic acid, minimizing the pH change.

Question 17

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

Accepted Answer

The pH is greater than 7 because the conjugate base of the weak acid hydrolyzes to produce OH$$^-.$$

Buffers: Properties, Calculations, and Titration Applications

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