Question 1

Which equation is used to calculate the pH of a buffer solution during the titration of a weak acid with a strong base, before the equivalence point?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log \left( \frac{[\mathrm{A}^-]}{[\mathrm{HA}]} \right)$$

Question 2

A student titrates 25.00 mL of 0.135 M formic acid ($$\mathrm{HCO}_2\mathrm{H}$$, $$K_a = 1.8 	imes 10$$^{-4}$$) with 0.250 M NaOH. What volume of NaOH is required to reach the equivalence point?

Accepted Answer

$$13.5\ \mathrm{mL}$$

Question 3

At the half-equivalence point during the titration of a weak acid with a strong base, which of the following is true?

Accepted Answer

$$[\mathrm{HA}] = [\mathrm{A}^-]$$

Question 4

What is the pH at the equivalence point when titrating 25.00 mL of 0.135 M formic acid ($$K_a = 1.8 	imes 10$$^{-4}$$) with 0.250 M NaOH?

Accepted Answer

$$8.34$$

Question 5

Which of the following best describes the solution at the equivalence point in the titration of a weak acid with a strong base?

Accepted Answer

A solution of the weak acid's conjugate base

Question 6

During a titration, after the equivalence point has been reached, what primarily determines the pH of the solution?

Accepted Answer

The excess strong base added

Question 7

Which calculation would you use to determine the pH after the equivalence point in a weak acid-strong base titration?

Accepted Answer

$$\mathrm{pH} = 14 - \mathrm{pOH}$$,\ \mathrm{where}\ \mathrm{pOH} = -\log [\mathrm{OH}^-]_{	ext{excess}}$

Question 8

A titration curve for a weak acid with a strong base shows a buffer region. What chemical process is responsible for this buffer region?

Accepted Answer

The formation of a buffer from the weak acid and its conjugate base

Question 9

How can you experimentally determine the $$K_a of an $$unknown weak acid using titration data?

Accepted Answer

Measure the pH at the half-equivalence point; $$\mathrm{pH} = \mathrm{p}K_a$$

Question 10

Which of the following best describes the pH at the equivalence point for the titration of a strong acid with a strong base?

Accepted Answer

pH $$= 7$$

Question 11

A buffer is formed during the titration of a weak acid with a strong base. Which equation would you use to calculate the pH in this region?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log \left( \frac{[\mathrm{A}^-]}{[\mathrm{HA}]} \right)$$

Question 12

If you titrate a weak acid with a strong base and monitor the pH, what does the pH at the half-equivalence point tell you?

Accepted Answer

The $$pK_a of $$the acid

Question 13

Which of the following is the correct net ionic equation for the reaction at the equivalence point in the titration of formic acid with NaOH?

Accepted Answer

$$\mathrm{HCO}_2\mathrm{H} (aq) + \mathrm{OH}^- (aq) \rightarrow \mathrm{HCO}_2^- (aq) + \mathrm{H}_2\mathrm{O} (l)$$

Question 14

A titration curve for a weak acid with a strong base is being analyzed. What feature of the curve allows you to determine the $$pK_a of $$the acid?

Accepted Answer

The pH at the half-equivalence point

Question 15

Which of the following steps is NOT necessary when calculating the pH at the equivalence point for a weak acid-strong base titration?

Accepted Answer

Use the Henderson-Hasselbalch equation

Question 16

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

Accepted Answer

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

Question 17

A student adds excess NaOH to a solution of formic acid after the equivalence point. Which calculation gives the pH?

Accepted Answer

$$\mathrm{pH} = 14 - \mathrm{pOH}$$,\ \mathrm{where}\ \mathrm{pOH} = -\log [\mathrm{OH}^-]_{	ext{excess}}$

Question 18

Which of the following is a correct method for finding the volume of titrant needed to reach the equivalence point in a titration?

Accepted Answer

$$V_{	ext{base}} = \frac{M_{	ext{acid}} 	imes V_{	ext{acid}}}{M_{	ext{base}}}$$

Acid-Base Titrations II: Weak Acid–Strong Base Titrations

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