Question

Identify the incorrect statement regarding the volumetric estimation of $FeS{O_4}$.
A. $KMn{O_4}$ can be used in aqueous $HCl$
B. ${K_2}C{r_2}{O_7}$ can be used in aqueous $HCl$
C. $KMn{O_4}$ can be used in aqueous ${H_2}S{O_4}$
D. ${K_2}C{r_2}{O_7}$ can be used in aqueous ${H_2}S{O_4}$

Answer 1

We must remember that volumetric estimation is a quantitative chemical estimation method. In this method, the unknown concentration of the analyte is being determined by the measurement of the volume of the known solution. Or we can say that this process involves measurement of the volume of a known solution combining with the other one is known proportion.

Complete answer:
From the knowledge of volumetric estimation, we can understand that the incorrect statement to this question will be option A, $KMn{O_4}$ can be used in aqueous $HCl$.
In detail, $KMn{O_4}$ cannot be used in the volumetric estimation of $FeSO_4$ in the presence of hydrochloric acid.
This is due to the difference that lies in the strength between hydrochloric acid and oxalic acid. Hydrochloric acid is comparatively very much stronger than the oxalic acid thus this will result in the reaction between $KMn{O_4}$ and hydrochloric acid which in turn will form corresponding chlorides of potassium and manganese along with the liberation of chlorine gas during the reaction.
This will disturb our redox (oxidation-reduction) titration due to the simple fact that the previous reaction with hydrochloric acid reduces the amount left of $KMn{O_4}$ to react with oxalic acid.
The chemical reaction that takes place is shown below:
$KMn{O_4} + {\text{ }}16HCl \to 2KCl{\text{ }} + {\text{ }}2MnC{l_2} + {\text{ }}8{H_2}O{\text{ }} + {\text{ }}5C{l_2}$
Hence the correct answer as you guys can guess by now is A.

Note:
We must know that the ferrous sulfate $\left( {FeS{O_4}} \right)$ is a compound which is highly used in the pharmaceutical industry for the development of medicine which deals with iron deficiency. Due to this, the estimation of ferrous sulfate is of great importance as different medicines will have different concentrations of this compound according to the patient’s requirement.
Also we know $HCl$ is a reducing agent and ${K_2}C{r_2}{O_7}$ is an oxidizing agent. Therefore, hydrogen chloride reacts with potassium dichromate to give chlorine and some other by-products. We can use this reaction to produce chlorine in the laboratory.