Q: During the titration of 40.00 mL of 0.1000 M HPr with 0.1000 M NaOH, what is the pH at the half-equivalence point? ($$K_a$$ for HPr = $$1.3 \times 10$$^{-5}$$)

$$\text{pH} = \text{p}K_a = -\log(1.3 \times 10$$^{-5}$$)$$

Question 1

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

Accepted Answer

The point where the moles of acid equal the moles of base added.

Question 2

Given 100.0 mL of 0.102 M acetic acid ($$K_a = 1.8 	imes 10$$^{-5}$$) titrated with 0.100 M NaOH, what is the volume of NaOH required to reach the equivalence point?

Accepted Answer

$$102\ 	ext{mL}$$

Question 3

During the titration of 40.00 mL of 0.1000 M HPr with 0.1000 M NaOH, what is the pH at the half-equivalence point? ($$K_a$$ for HPr = $$1.3 	imes 10$$^{-5}$$)

Accepted Answer

$$	ext{pH} = 	ext{p}K_a = -\log(1.3 	imes 10$$^{-5}$$)$$

Question 4

A student titrates 200.0 mL of dilute HNO$$_2$$ with 0.100 M NaOH. What is the main purpose of this titration?

Accepted Answer

To determine the molarity of the HNO$$_2$$ solution.

Question 5

Which equation correctly represents the reaction between acetic acid and sodium hydroxide during titration?

Accepted Answer

$$\mathrm{HC_2H_3O_2} + \mathrm{NaOH} \rightarrow \mathrm{C_2H_3O_2^-} + \mathrm{H_2O} + \mathrm{Na^+}$$

Question 6

If 100.0 mL of 0.102 M acetic acid is mixed with 200.0 mL of 0.10 M NaOH, what species will be present in excess after the reaction goes to completion?

Accepted Answer

NaOH

Question 7

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 8

In a titration curve of a weak base with a strong acid, what is the expected pH at the equivalence point?

Accepted Answer

Less than 7

Question 9

A 40.0 mL sample of 0.10 M H$$_2SO$_3 is $$titrated with 0.10 M NaOH. How many moles of NaOH are required to reach the first equivalence point?

Accepted Answer

$$0.0040\ 	ext{mol}$$

Question 10

Which of the following is the correct formula to calculate the pH of a solution containing a weak acid and its conjugate base (buffer solution)?

Accepted Answer

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

Question 11

During the titration of a weak base with a strong acid, which of the following best describes the shape of the titration curve?

Accepted Answer

Starts at high pH, drops sharply near equivalence, then levels off at low pH.

Question 12

If you titrate 100.0 mL of 0.102 M acetic acid with 0.10 M NaOH and measure a pH of 4.92 after adding 50.0 mL of NaOH, what is the main species present in solution?

Accepted Answer

A mixture of acetic acid and acetate ion (buffer)

Question 13

Which of the following best explains why a buffer region appears in the titration curve of a weak acid with a strong base?

Accepted Answer

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

Question 14

A titration curve for a strong acid with a strong base shows a sharp jump in pH at the equivalence point. What is the pH at the equivalence point?

Accepted Answer

7.0

Question 15

Which of the following is the correct expression for the acid dissociation constant ($$K_a) of $$acetic acid?

Accepted Answer

$$K_a = \frac{[\mathrm{H}^+][\mathrm{C_2H_3O_2^-}]}{[\mathrm{HC_2H_3O_2}]}$$

Question 16

If you titrate 40.00 mL of 0.1000 M HPr with 0.1000 M NaOH and the $$K_a$$ for HPr is $$1.3 	imes 10$$^{-5}$$, what is the pH at the equivalence point?

Accepted Answer

$$	ext{pH} = 7 + \frac{1}{2}(	ext{p}K_w - \log K_a)$$

Acid-Base Titrations: Calculations, Curves, and Concepts

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