Q: A 50.00 mL sample of 0.10 M acetic acid ($$\mathrm{HC_2H_3O_2}) is $$titrated with 0.10 M NaOH. What is the pH after adding 25.00 mL of NaOH? ($$K_a = 1.8 \times 10$$^{-5}$$)

pH = pK_a = $$-\log(1.8 \times 10$$^{-5}$$) = 4.74$$

Question 1

Which of the following statements best explains why the pH at the equivalence point of a strong acid-strong base titration is always 7.00 at 25°C?

Accepted Answer

Because the strong acid and strong base completely neutralize each other, leaving only water and a neutral salt, so the pH is determined by the auto-ionization of water.

Question 2

A 50.00 mL sample of 0.10 M acetic acid ($$\mathrm{HC_2H_3O_2}) is $$titrated with 0.10 M NaOH. What is the pH after adding 25.00 mL of NaOH? ($$K_a = 1.8 	imes 10$$^{-5}$$)

Accepted Answer

pH = pK_a = $$-\log(1.8 	imes 10$$^{-5}$$) = 4.74$$

Question 3

During the titration of a weak acid with a strong base, which region of the titration curve corresponds to the buffer region?

Accepted Answer

The region before the equivalence point where both the weak acid and its conjugate base are present.

Question 4

Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

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

Question 5

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

Accepted Answer

Because the conjugate base of the weak acid hydrolyzes to produce OH− ions.

Question 6

A student titrates 0.10 M NH$$_3$$ with 0.10 M HCl. At the half-equivalence point, what is the relationship between $$[NH_3$]$$ and $$[NH_4$^+]$$?

Accepted Answer

$$[NH_3$] = [NH_4$^+]$$

Question 7

Which indicator would be most appropriate for detecting the equivalence point in the titration of a strong acid with a strong base?

Accepted Answer

Phenolphthalein, because its color change interval overlaps the equivalence point pH.

Question 8

What is the main reason a buffer resists changes in pH upon addition of small amounts of acid or base?

Accepted Answer

The buffer contains both a weak acid and its conjugate base, which neutralize added H$$^+ or OH$^-.$$

Question 9

A diprotic acid ($$H_2A) is $$titrated with a strong base. How many equivalence points and buffer regions are observed on the titration curve?

Accepted Answer

Two equivalence points and two buffer regions.

Question 10

Which of the following best describes the color change of an acid-base indicator?

Accepted Answer

It changes color over a range of about 2 pH units centered around its p$$K_a.$$

Question 11

After the equivalence point in the titration of acetic acid with NaOH, what species primarily determines the pH?

Accepted Answer

Excess OH$$^-$$ from the added NaOH.

Question 12

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

Accepted Answer

Calculate the hydrolysis of the conjugate acid using $$K_a$$ and an ICE table.

Question 13

A buffer is prepared by mixing equal moles of acetic acid and sodium acetate. What is the resulting pH?

Accepted Answer

pH = p$$K_a of $$acetic acid

Question 14

Which of the following best explains why methyl red is not a suitable indicator for the titration of a strong base with a strong acid?

Accepted Answer

Its color change interval does not overlap the equivalence point pH.

Question 15

What is the correct expression for the percent ionization of a weak acid?

Accepted Answer

$$\frac{[H_3O^+]_{eq}}{[HA]_i} 	imes 100$$

Question 16

Which of the following is true about the titration curve of a weak base with a strong acid?

Accepted Answer

The equivalence point occurs at pH \u003c 7 due to the hydrolysis of the conjugate acid.

Question 17

Which formula would you use to calculate the pH at the first equivalence point of a diprotic acid titration?

Accepted Answer

$$[H_3O^+] = \sqrt{K_{a1} K_{a2}}$$

Question 18

A universal indicator is used to measure the pH of a solution. What is a key property of a universal indicator?

Accepted Answer

It is a mixture of indicators that changes color over the entire pH range (0–14).

Acid-Base Titrations and Indicators: Aqueous Ionic Equilibria

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