Question 1

Which of the following best describes the role of an acid-base indicator in a titration?

Accepted Answer

It changes color at a specific pH, signaling the endpoint of the titration.

Question 2

A student is titrating a strong acid with a strong base. Which indicator would be most appropriate if the equivalence point occurs at pH 7?

Accepted Answer

Bromothymol blue ($\mathrm{pH~range:~6.0-7.6}$)

Question 3

The color change of an acid-base indicator occurs when:

Accepted Answer

The pH equals the indicator's $\mathrm{p}K_a$.

Question 4

If methyl red ($\mathrm{p}K_a = 5.0$) is used in a titration, at what pH will the indicator be half yellow and half red?

Accepted Answer

$\mathrm{pH} = 5.0$

Question 5

A solution being titrated has a pH of 9.0. Which indicator would be most suitable to detect the endpoint?

Accepted Answer

Phenolphthalein ($\mathrm{pH~range:~8.2-10.0}$)

Question 6

During a titration, the equivalence point is reached when:

Accepted Answer

The amount of acid equals the amount of base added.

Question 7

Which of the following indicators would be least suitable for a titration with an equivalence point at pH 4?

Accepted Answer

Phenolphthalein ($\mathrm{pH~range:~8.2-10.0}$)

Question 8

Bromothymol blue has a $\mathrm{p}K_a$ of 7.1. At what pH will the indicator be present in equal amounts of its acidic and basic forms?

Accepted Answer

$\mathrm{pH} = 7.1$

Question 9

A student uses bromophenol blue ($\mathrm{p}K_a = 4.1$) in a titration. If the solution being titrated has a pH of 6.0, what color will the indicator show?

Accepted Answer

Blue

Question 10

Which statement best explains why the color change of an indicator is not always at the equivalence point?

Accepted Answer

The indicator's $\mathrm{p}K_a$ may not match the pH at the equivalence point.

Question 11

A titration curve shows a sharp increase in pH at the equivalence point. What does this suggest about the acid and base involved?

Accepted Answer

Both are strong.

Question 12

If an indicator has a $\mathrm{p}K_a$ of 4.7, what is the approximate pH range over which it changes color?

Accepted Answer

$2.7-6.7$

Question 13

Which indicator would be best for detecting the endpoint in a titration where the equivalence point is at pH 5?

Accepted Answer

Methyl red ($\mathrm{pH~range:~4.2-6.3}$)

Question 14

A student is titrating a weak acid with a strong base. The equivalence point is at pH 9. Which indicator should be chosen?

Accepted Answer

Phenolphthalein ($\mathrm{pH~range:~8.2-10.0}$)

Question 15

If the pH of a solution is below the $\mathrm{p}K_a$ of the indicator, which form predominates?

Accepted Answer

The acidic form

Question 16

A titration uses methyl orange as the indicator. If the solution is orange, what is the likely pH?

Accepted Answer

$\mathrm{pH}$ is between $3.4$ and $4.4$

Question 17

Which of the following is true about the color change interval of an indicator?

Accepted Answer

It is typically about two pH units centered around the indicator's $\mathrm{p}K_a$.

Question 18

A solution being titrated with bromothymol blue ($\mathrm{p}K_a = 7.1$) has a pH of 8.0. What color will the indicator show?

Accepted Answer

Blue

Question 19

Why is it important to choose an indicator whose color change range matches the equivalence point of a titration?

Accepted Answer

To ensure the color change occurs at the endpoint, providing accurate titration results.

Acid-Base Indicators in Titrations

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