Chapter 19, Problem 93A

a)

Interpretation Introduction

Interpretation : The pH at the end point of this titration is to be calculated.

Concept Introduction : The negative logarithm of the concentration of hydrogen ions is the pH of a solution. The formula to calculate pH is given as

  $\text{pH=}-{\text{log[H}}^{\text{+}}\text{]}$

Answer to Problem 93A

The pH at the end point is $8.73$

Explanation of Solution

The concentration of $\text{NaOH}$ is $\text{0}\text{.1}\text{M}$.

The volume of ethanoic acid is $\text{50}\text{mL}$.

The reaction taking place between sodium hydroxide and ethanoic acid is given as

  ${\text{CH}}_{\text{3}}\text{COOH}+\text{NaOH}\to {\text{CH}}_{\text{3}}\text{COONa}+{\text{H}}_{\text{2}}\text{O}$

Since the molar ratio is 1:1.

To neutralize the 50 ml of ethanoic acid, there is a need of 50 ml of sodium hydroxide.

The endpoint is reached when 50 ml of sodium hydroxide is added.

With the help of data, pH at 50 ml of sodium hydroxide is detected.

So, the pH at the end point is

The graph is plotted between volume of sodium hydroxide and pH.

  

b)

Interpretation Introduction

Interpretation : The acid-base indicators that could be used to determine the end point in this titration is to be identified.

Concept Introduction : An indicator is any substance that alters color to signal the presence or absence of a chemical species in a solution, such as an acid or an alkali.

Answer to Problem 93A

Phenolphthalein or phenol red can be used as indicators for acid-base titration.

Explanation of Solution

An indicator is any substance that alters color to signal the presence or absence of a chemical species in a solution, such as an acid or an alkali.

The titration's end occurs when the indicator's color changes.

For acid-base titration, the end point is detected by indicators like phenolphthalein or phenol red.