Question

Aqueous solution of $HNO _{3}, KOH , CH _{3} COOH$ and $CH _{3} COONa$ of identical concentration are provided. The pair (s) of solutions which form a buffer upon mixing is (are)

• A. $HNO _{3}$ and $CH _{3} COOH$
• B. $KOH$ and $CH _{3} COONa$
• C. $HNO _{3}$ and $CH _{3} COONa$
• D. $CH _{3} COOH$ and $CH _{3} COONa$

Answer 1

Answer: (C), (D)

$•$ A Weak acid and its salt with a strong base forms a buffer.
$•$ $HNO _{3}$ being a strong acid, displaces weaker acid $CH _{3} COOH$.
$HNO _{3}+ CH _{3}- COO ^{-} \rightleftharpoons CH _{3}- COOH + NO _{3}^{-}$
If $\left[ CH _{3} COO ^{-}\right]>\left[ HNO _{3}\right]$, then solution contains weak acid $\left( CH _{3} COOH \right)$ and its conjugate base $\left( CH _{3} COO ^{-}\right) $