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 $O{H}^{-}$ 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.
$H_3{O}^{+}+A^{-}\rightleftharpoons H_{2}O+HA$
$-OH+HA\to H_{2}O+A^{-}$
If acid is added, it reacts with $A^{-}$to form undissociated $H$ A. Similarly, if base/alkali is added, $O{H}^{-}$combines with HA to give $H_{2}O$ and $A^{-}$and thus, maintains the acidity/ alkalinity of buffer solution.