Question

Buffer solutions have constant acidity and alkalinity because

• A. these give unionised acid or base on reaction with added acid or alkali
• B. acids and alkalies in these solutions are shielded from attack by other ions
• C. they have large excess of $H^+$ or $OH^-$ ions
• D. they have fixed value of pH

Answer 1

Answer: (A)

these give unionised acid or base on reaction with added acid or alkali

Answer 2

If small amount of an acid or alkali is added to a buffer solution, it converts them into unionised acid or base. Thus, its pH remains unaffected or in other words its acidity/alkalinity remains constant, e.g.
\hspace15mm H_3O^+ + A^- \rightleftharpoons H_2O + HA
\hspace 18 mm ^-OH + HA \rightarrow H_2O + A^-
If acid is added, it reacts with $A^-$ to form undissociated H A. Similarly, if base/alkali is added, $OH^-$ combines with HA to give $H_2O$ and $A^-$ and thus, maintains the acidity/ alkalinity of buffer solution.