Question

If a drop of decinormal HCI is added to a mixture of weak acid and its strong salt then in the following condition which option is correct?

(a) Very high change in H^+ ions

(b) High change in H^+ ions

(c) Slight change in H^+ ions

(d) No change in H^+ ions

The question was asked during an interview for a job.

Origin of the question is Buffers topic in division Introduction to Fermentation Processes & Media for Industrial Fermentation of Bioprocess Engineering

Answer 1

The correct answer is:

(c) Slight change in H⁺ ions

Explanation: When a decinormal (0.1 M) solution of HCl is added to a mixture of a weak acid and its strong salt (a buffer solution), the buffer system resists significant changes in the pH by neutralizing the added H⁺ ions. The weak acid and its conjugate base (from the strong salt) can react with the H⁺ ions, minimizing the change in the concentration of H⁺ ions. However, since the buffer capacity is not infinite, there will still be a slight change in the concentration of H⁺ ions, but it will be much smaller compared to the addition of the acid to a non-buffered solution.

Thus, the buffer will cause only a slight change in the H⁺ ion concentration, not a high or very high change.