Question

Which of the following plot represents the graph of pH against volume of alkali added in the titration of $NaOH$ and $HCl$
A.

B.

C.

D.

Answer 1

Hint: We need to know that \[pH\] is mainly used to find out the solution which is acidic, basic or neutral. And the range of \[pH\] from one to $14$ . The solution is neutral if the \[pH\] is $7$ . And if it is less than $7$ means, the solution is acidic and \[pH\] is greater than seven means, the solution is basic. And \[pH\] mainly measures the relative amount of free hydrogen which is present in the water.

Complete answer:
While adding alkali to acid, there occurs a change in \[pH\]. And the acidity of acid becomes decreasing and the basicity will start to increase. But there is no sudden increase in the \[pH\] Hence, option (A) is incorrect.
Here, the base is added to the acid solution. Hence, \[pH\]of the solution is low at the initial stage. But, in this graph, the plot of \[pH\] starts from its higher range. Hence, option (B) is correct.
When sodium hydroxide is added to hydrochloric acid, \[pH\] of the solution remains the same at the initial stage. After that it suddenly increases \[pH\]. Then it became almost the same. After that there is no change in the \[pH\]. Therefore, the graph of pH against volume of alkali added in the titration of $NaOH$ and $HCl$ is,

Hence, option (C) is correct.
This is not the correct graphical representation of pH against volume. Hence, the option (D) is incorrect.

Hence, option (C) is correct.

Note:
We need to know that when the alkali and acid are mixing in the right amounts, the reaction is wound up with the formation of a neutral solution. If water or base is added to an acid, the pH of the acid will be increasing. Because, there is a decrease in the acidity and the acid becomes less acidic. If the water is added to an alkali solution, the pH of the base becomes near $7$ due to the decrease in the concentration of hydroxide ions.