Question

Why is $HCl$ not used for titration? $HN{O_3}$ .

Answer 1

Hint : $HCl$ is not used in the titration with $KMn{O_4}$ because it is not able to make the solution acidic in nature. It gets itself oxidised easily and hence does not provide sufficient hydrogen ions to make the solution suitable for titration.

Complete Step By Step Answer:
Generally we add the $HCl$ to acidify the $KMn{O_4}$ solution. But when we add a few drops of $HCl$ to the potassium permanganate solution then the $HCl$ gets oxidised. This is because $KMn{O_4}$ is a strong oxidising agent. It oxidises the $HCl$ to evolve chlorine gas. Therefore the medium does not become acidic. But for titration we need an acidic medium. Hence we generally do not add weak acid for titration. The following reaction takes place when $HCl$ is added to $KMn{O_4}$ solution.
$2KMn{O_4}{\text{ + 16HCl }}\xrightarrow{{}}{\text{ 2KCl + 2MnC}}{{\text{l}}_2}{\text{ + 5C}}{{\text{l}}_2}{\text{ + }}{{\text{H}}_2}{\text{O}}$

Additional Information:
We prefer to use ${H_2}S{O_4}$ over the use of $HCl$ . This is because ${H_2}S{O_4}$ is a strong acid and makes the solution more acidic than $HCl$ . Thus the end results of the titration are more accurate when we use ${H_2}S{O_4}$ in the titration. ${H_2}S{O_4}$ gives two ions of hydronium while $HCl$ gives only one hydronium ion. There is another like $HCl$ which is $HN{O_3}$ . $HN{O_3}$ is also not used in the titration process. Both $HCl$ and $HN{O_3}$ are also called mineral acids.

Note :
Hydrochloric acid is weak acid in comparison to sulphuric acid. It is recommended to use sulphuric acid. Also it doesn't get easily oxidised by potassium permanganate. While using hydrochloric acid, in the end of the reaction, the final value of indicator used may differ in what actually used in the reaction. Thus it makes our calculations hectic. Also it oxidised to produce chlorine gas.