Question

Which of the following pairs constitutes a buffer?

• A. $HNO_2$ & $NaNO_2$
• B. $NaOH$ & $NaCl$
• C. $HNO_3$ & $NH_4NO_3$
• D. $HCl$ & $KCl$

Answer 1

Answer: (A)

$HNO_2$ & $NaNO_2$

Answer 2

The correct answer is A:$HNO_2\space and\space NaNO_2$
HNO2 and NaNO2 constitutes a buffer solution. Buffer solutions are a mixture of weak acids and their salts or weak bases and their salts. Among all the compounds mentioned above HCl and HNO3 are strong acids and NaOH is a a strong base. Therefore, these can not form buffer solutions. On the other hand, HNO 2 is a weak acid and NaNO2 is the salt formed by HNO2 and NaOH. Hence, these constitute a buffer solution. Buffer solutions can resist a change in their pH because of the equilibrium between the acid and its conjugate base or base and its conjugate acid.