Question

Which of the following solutions when added to 1L of a 0.1 M CH₃COOH solution will cause no change either in the degree of dissociation of CH₃COOH or in the pH of the solution. Ka = 1.8 × 10⁻¹⁵for CH₃COOH.

A. 3 mM HCOOH (Ka = 6 × 10⁻⁴)
B. 0.1 M CH₃COONa
C. 1.34 mM HCl
D. 0.1 M CH₃COOH

Answer 1

Adding 0.1 M CH₃COOH solution will cause no change in the degree of dissociation of CH₃COOH or in the pH of the solution. The correct option is (D).

Step-by-step explanation:

In order to cause no change in the degree of dissociation of CH₃COOH or in the pH of the solution, we need to add a solution that does not affect the concentration of CH₃COOH or the concentration of H₃O⁺ ions. Let's analyze each option:

A. 3 mM HCOOH: Since HCOOH is a weak acid with a different Ka value than CH₃COOH, it will affect the degree of dissociation and pH.

B. 0.1 M CH₃COONa: This is a salt of CH₃COOH, and adding it to the solution will not affect the degree of dissociation or pH.

C. 1.34 mM HCl: HCl is a strong acid that will increase the concentration of H₃O⁺ ions and therefore lower the pH.

D. 0.1 M CH₃COOH: Since we are adding the same acid, the concentration and degree of dissociation will remain the same, and the pH will not change.

Therefore, option D (0.1 M CH₃COOH) will cause no change in the degree of dissociation of CH₃COOH or in the pH of the solution.