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)

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.
$ H _{3} O ^{+}+ A ^{-} \rightleftharpoons H _{2} O + HA $
$- OH + HA \rightarrow H _{2} O + A ^{-}$
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 $H _{2} O$ and $A ^{-}$and thus, maintains the acidity/ alkalinity of buffer solution.