Q: Which indicator would be most appropriate for a titration where the equivalence point is expected at pH 8.7?

Phenolphthalein ($$\text{p}K_{\text{In}} \approx 9.7)$$

Q: A 50.0 mL sample of 1.0 M acetic acid (a weak acid, $$K_a = 1.8 \times 10$$^{-5}$$) is titrated with 1.0 M NaOH. What is the pH at the half-equivalence point?

$$\text{pH} = \text{p}K_a = 4.74$$

Q: During a titration, the indicator changes color when:

$$\text{pH} = \text{p}K_{\text{In}} \pm 1$$

Q: Why is phenolphthalein not a suitable indicator for the titration of a strong acid with a strong base if the equivalence point is at pH 4?

Its color change range ($$\text{pH} \approx 8.2 to$$ $$10.0) $$does not overlap with the equivalence point.

Q: Which equation is used to calculate the pH of a buffer solution during the titration of a weak acid with a strong base?

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

Q: If you titrate 50.0 mL of 0.10 M acetic acid with 0.10 M NaOH, what is the pH after adding 25.0 mL of NaOH? ($$K_a = 1.8 \times 10$$^{-5}$$)

$$\text{pH} = \text{p}K_a = 4.74$$

Q: A titration of 25.0 mL of 0.100 M HCl with 0.100 M NaOH is performed. What is the pH after adding 30.0 mL of NaOH?

$$\text{pOH} = -\log \left( \frac{5.0 \times 10$$^{-4}$$}{55.0 \times 10$$^{-3}$$} \right) = 2.04$$, so $$\text{pH} = 11.96$$

Question 1

During the titration of a strong acid (HCl) with a strong base (NaOH), what is the pH at the equivalence point?

Accepted Answer

$$	ext{pH} = 7$$

Question 2

Which indicator would be most appropriate for a titration where the equivalence point is expected at pH 8.7?

Accepted Answer

Phenolphthalein ($$	ext{p}K_{	ext{In}} \approx 9.7)$$

Question 3

A 50.0 mL sample of 1.0 M acetic acid (a weak acid, $$K_a = 1.8 	imes 10$$^{-5}$$) is titrated with 1.0 M NaOH. What is the pH at the half-equivalence point?

Accepted Answer

$$	ext{pH} = 	ext{p}K_a = 4.74$$

Question 4

Which of the following best describes the shape of the titration curve for a weak acid titrated with a strong base?

Accepted Answer

The curve starts at a higher pH than a strong acid, has a buffer region, and the equivalence point is above pH 7.

Question 5

During a titration, the indicator changes color when:

Accepted Answer

$$	ext{pH} = 	ext{p}K_{	ext{In}} \pm 1$$

Question 6

A student titrates 25.0 mL of 0.100 M HCl with 0.100 M NaOH. What volume of NaOH is required to reach the equivalence point?

Accepted Answer

$$25.0\ 	ext{mL}$$

Question 7

In a titration of 50.0 mL of 1.0 M NH$$_3 (a $$weak base, $$K_b = 1.8 	imes 10$$^{-5}$$) with 1.0 M HCl, what is the major species present at the equivalence point?

Accepted Answer

NH$$_4^+$$

Question 8

Why is phenolphthalein not a suitable indicator for the titration of a strong acid with a strong base if the equivalence point is at pH 4?

Accepted Answer

Its color change range ($$	ext{pH} \approx 8.2 to$$ $$10.0) $$does not overlap with the equivalence point.

Question 9

A buffer solution is formed during the titration of a weak acid with a strong base. At what point is the buffer capacity the greatest?

Accepted Answer

At the half-equivalence point

Question 10

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

Accepted Answer

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

Question 11

A titration curve for a weak base with a strong acid will have its equivalence point:

Accepted Answer

Below pH 7

Question 12

If you titrate 50.0 mL of 0.10 M acetic acid with 0.10 M NaOH, what is the pH after adding 25.0 mL of NaOH? ($$K_a = 1.8 	imes 10$$^{-5}$$)

Accepted Answer

$$	ext{pH} = 	ext{p}K_a = 4.74$$

Question 13

Which of the following statements about the equivalence point and the end point in a titration is correct?

Accepted Answer

The equivalence point is when stoichiometric amounts of acid and base have reacted; the end point is when the indicator changes color.

Question 14

A titration of 25.0 mL of 0.100 M HCl with 0.100 M NaOH is performed. What is the pH after adding 30.0 mL of NaOH?

Accepted Answer

$$	ext{pOH} = -\log \left( \frac{5.0 	imes 10$$^{-4}$$}{55.0 	imes 10$$^{-3}$$} ight) = 2.04$$, so $$	ext{pH} = 11.96$$

Question 15

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

Accepted Answer

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

Question 16

During a titration, why is it important to choose an indicator whose $$	ext{p}K_{	ext{In}} is $$close to the pH at the equivalence point?

Accepted Answer

To ensure the color change occurs as close as possible to the equivalence point.

Question 17

A titration curve shows a sudden, steep rise in pH near the equivalence point. What does this indicate about the acid and base involved?

Accepted Answer

Both the acid and base are strong.

Question 18

In a titration of a weak base with a strong acid, which equation would you use to calculate the pH before the equivalence point?

Accepted Answer

$$	ext{pOH} = 	ext{p}K_b + \log \left( \frac{[	ext{BH}^+]}{[	ext{B}]} ight)$$

Question 19

A solution contains both HIn and In$$^-$$, the acid and base forms of an indicator. At what ratio of $$\frac{[	ext{In}^-]}{[	ext{HIn}]}$$ will the color change be most noticeable?

Accepted Answer

When $$\frac{[	ext{In}^-]}{[	ext{HIn}]} = 1$$

Titration Curves and Acid-Base Reactions: Study Notes

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