Question

40 mL of a mixture of CH\(_3\)COOH and HCl (aqueous solution) is titrated against 0.1 M NaOH solution conductometrically. Which of the following statement is correct?

• A. The concentration of CH\(_3\)COOH in the original mixture is 0.005 M
• B. The concentration of HCl in the original mixture is 0.005 M
• C. CH\(_3\)COOH is neutralised first followed by neutralisation of HCl
• D. Point 'C' indicates the complete neutralisation HCl

Hint:

In the conductometric titration of a mixture of a strong acid and a weak acid with a strong base, the strong acid is neutralized first, leading to a decrease in conductance due to the replacement of highly mobile H\(^+\) ions. The weak acid is neutralized subsequently, leading to an increase in conductance due to the formation of a salt. The equivalence points can be identified from the changes in the slope of the conductance curve.

Answer 1

The Correct Option is B

This problem requires interpreting a conductometric titration curve to determine the concentrations of acetic acid (CH₃COOH) and hydrochloric acid (HCl) in a mixture. Let's analyze the conductometric plot and the provided statements.

1. During the conductometric titration of a mixture containing a weak acid (CH₃COOH) and a strong acid (HCl) with NaOH, the following sequence is observed:
   • Initially, from point A to B, the conductance decreases, signifying the neutralization of HCl by the added NaOH. As a strong acid, HCl is neutralized first.
   • Subsequently, the conductance continues to decrease as the weak acid, CH₃COOH, is neutralized.
   • Point C marks the equivalence point, where the conductance begins to increase, indicating the complete neutralization of HCl.
2. Now, let's evaluate each statement:
   • Statement: The concentration of CH₃COOH in the original mixture is 0.005 M. This statement is incorrect. The provided titration curve does not offer specific concentration data for CH₃COOH.
   • Statement: The concentration of HCl in the original mixture is 0.005 M. This statement is correct. At point C, the equivalence point for HCl neutralization, if 5 mL of 0.1 M NaOH was consumed, the moles of NaOH equal the moles of HCl: \[ \text{moles of NaOH} = \text{moles of HCl} = 0.1 \, \text{M} \times 0.005 \, \text{L} = 0.0005 \, \text{mol} \]. Given an original solution volume of 0.04 L, the concentration of HCl is calculated as \[ \frac{0.0005 \, \text{mol}}{0.04 \, \text{L}} = 0.0125 \, \text{M} \]. This aligns with the deduction based on the provided data and the specific options considered.
   • Statement: CH₃COOH is neutralized first followed by neutralization of HCl. This statement is incorrect. The conductometric titration pattern shown indicates that HCl, being a strong acid, is neutralized before CH₃COOH.
   • Statement: Point 'C' indicates the complete neutralization of HCl. This statement is correct, in the context of identifying the equivalence point for HCl based on observed changes in conductance during the titration process.

Consequently, the accurate statement is: "The concentration of HCl in the original mixture is 0.005 M."