Question 1

Which of the following best explains why the initial pH of a weak acid–strong base titration is higher than that of a strong acid–strong base titration, assuming equal concentrations and volumes?

Accepted Answer

Weak acids do not fully dissociate in water, resulting in a lower initial $$[\mathrm{H}_3\mathrm{O}^+]$$ concentration.

Question 2

During the titration of 25.00 mL of 0.200 M acetic acid ($$\mathrm{CH}_3\mathrm{COOH}) $$with 0.200 M NaOH, what is true at the half-equivalence point?

Accepted Answer

The concentration of $$\mathrm{CH}_3\mathrm{COOH}$$ equals the concentration of $$\mathrm{CH}_3\mathrm{COO}^-.$$

Question 3

Which equation would you use to calculate the pH at the half-equivalence point during the titration of a weak acid with a strong base?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a$$

Question 4

Why is the pH at the equivalence point greater than 7 in the titration of a weak acid with a strong base?

Accepted Answer

The conjugate base formed hydrolyzes with water to produce $$\mathrm{OH}^-$$ ions.

Question 5

A student titrates 25.00 mL of 0.200 M $$\mathrm{NH}_3$$ with 0.200 M HCl. What is the main species present at the equivalence point?

Accepted Answer

$$\mathrm{NH}_4^+$$

Question 6

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

Accepted Answer

The endpoint is the pH at which the indicator changes color, which should closely match the equivalence point.

Question 7

In a titration of a weak acid with a strong base, which region of the titration curve is characterized by the presence of a buffer solution?

Accepted Answer

Between the initial point and the equivalence point, before all acid is neutralized.

Question 8

A chemist titrates 25.00 mL of 0.200 M acetic acid with 0.200 M NaOH. How many moles of NaOH are required to reach the equivalence point?

Accepted Answer

$$0.00500$$ mol

Question 9

Which of the following best describes the pH change near the equivalence point in a weak acid–strong base titration compared to a strong acid–strong base titration?

Accepted Answer

The pH rises more sharply and the equivalence point occurs at a higher pH.

Question 10

If a student uses phenolphthalein as an indicator for the titration of acetic acid with NaOH, why is this a suitable choice?

Accepted Answer

Phenolphthalein changes color in the pH range near the equivalence point of the titration.

Question 11

Which of the following is a correct statement about the calculation of total acid concentration in a weak acid solution?

Accepted Answer

It is the sum of the concentrations of dissociated and undissociated acid.

Question 12

A buffer solution is most effective when:

Accepted Answer

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

Question 13

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

Accepted Answer

$$\mathrm{pOH} = \mathrm{p}K_b$$

Question 14

Which of the following best explains why the titration curve for a weak acid–strong base titration has a buffer region?

Accepted Answer

Both the weak acid and its conjugate base are present in significant amounts before the equivalence point.

Question 15

A solution contains 0.100 M acetic acid and 0.100 M sodium acetate. What is the pH of this solution if $$\mathrm{p}K_a of $$acetic acid is 4.76?

Accepted Answer

$$4.76$$

Question 16

Which of the following is a key difference between the titration of a weak acid with a strong base and the titration of a strong acid with a strong base?

Accepted Answer

The equivalence point pH is greater than 7 for the weak acid–strong base titration.

Question 17

A titration curve for a weak base–strong acid titration shows a gradual decrease in pH until the equivalence point. What causes the pH to drop sharply at the equivalence point?

Accepted Answer

The weak base is completely neutralized, and excess strong acid is added.

Question 18

Which of the following best describes the chemical reaction occurring during the titration of acetic acid with sodium hydroxide?

Accepted Answer

$$\mathrm{CH}_3\mathrm{COOH} + \mathrm{OH}^- \rightarrow \mathrm{CH}_3\mathrm{COO}^- + \mathrm{H}_2\mathrm{O}$$

Acid-Base Titrations Involving Weak Acids and Bases

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