Question

Which of the following set of solutions could be used to prepare a buffer solution?
(A) $0.1\;M\,HCl\;and\;0.1\;M\,NaCl$
(B) $1\;M\,KHC{O_3}\;and1\;M\;KOH$
(C) $1\;M\;HN{O_2}\;and\,1\;M\;NaN{O_3}\,$
(D) $1\;M\,NaH{C_2}{O_4}\;and\,1\,M\;{H_2}{C_2}{O_4}$

Answer 1

The buffer solution is the so;ution consisting of the mixture of weak acid or base and its conjugate acid or base that maintain it $pH$ . There are few alternate names which are used to refer to buffer solutions such as $pH$ buffers or hydrogen ion buffers.

Complete Step By Step Answer:
The buffer solution is a solution that is able to maintain its $pH$ (hydrogen ion concentration) with only minor changes on the dilution or addition of a small amount of either base or acid. In other words , the solution consists of a mixture of a weak base or acid and its conjugate acid or base.
To identify if the given mixture of compounds is a buffer solution or not, we will check whether it contains weak or strong acid or base. Weak acids or base are those which partially dissociates into its ion in an aqueous solution or water whereas strong acid or base are those which fully dissociates into its ion in an aqueous solution.
In the following question the first two are not buffer solutions as they are the salt of strong acid and base. As we know that buffer solution contains weak acids or bases so the first option is incorrect.
Now in option $c$ , here $HN{O_2}$ is a weak acid but in $NaN{O_2}$ the $N{O_3}^ -$ ion is not the conjugate of the weak acid . The conjugate of the weak acid contains a base of appreciable strength which enables it to acquire ${H^ + }$ ions to some degree, helping to adjust the $pH$ which is the purpose of a buffer.
Here, $N{O_3}^ -$ ion has zero ability to gain ${H^ + }$ ions as its conjugate acid $HN{O_3}$ is very strong and hence could not adjust the pH. Thus, if the compound is $NaN{O_2}$ then we would have a buffer.
Moving to next two options, the option $d$ which is $NaH{C_2}{O_4}\;and\,{H_2}{C_2}{O_4}$ , is the buffer solution as first of all $NaH{C_2}{O_4}$ is the conjugate salt of weak acid and ${H_2}{C_2}{O_4}$ is the weak acid. So this is a buffer solution.
So, option $D$ is right.

Note:
Buffer solution used to maintain $pH$ for enzyme activity in many organisms. The absence of these buffers may lead to the enzyme action, loss in its properties or denature of the enzymes. This denaturation process can even permanently deactivate the catalytic action of enzymes.