Question

Conductometric titration curve of an equimolar mixture of $HCl$ and $HCN$ with $NaOH\left(aq\right)$ can be given as

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

The titration is an example of titration of mixture of acids against strong base $\left(NaOH\right)$.
When mixture of acid is titrated with $NaOH$, strong acid will react first followed by weak acid.

Here, $HCl$ will react with $NaOH$ in the start and get neutralised.
The neutralised reaction is,
$HCl+NaOH\to NaCl+H_{2}O$

During this reaction, the conductance of the solution gradually decreases due to the removal of $H^{+}$ ions of highly ionised $HCl$ to form unionised water. This will be the first
part of the graph.

When $HCl$ is finished $HCN$ starts reacting with $NaOH$.
Here, the neutralisation reaction is
$HCN+NaOH\to NaCN+H_{2}O$

During the neutralisation of weak acid the conductance increases marginally due to the salts $\left(NaCN\right)$ produced which will be the second part of graph.

After the equivalence point, the increase in conductance is appreciable due to the added $O{H}^{-}$ ions.

Thus, the conductance will decrease steeply and then increase marginally and again increase steeply.
Thus, option (d) is correct.