Question

In Carius method for the quantitative estimation of sulphur. it is estimated by__________.
A. $BaS$
B. $CaS{O_4}$
C. $BaS{O_4}$
D. $BaC{l_2}$

Answer 1

We know that quantitative analysis is an analysis method that is used to obtain the number of elements or molecules produced during a chemical reaction. We can say the Carius halogen method in analytical chemistry is used for the quantitative determination of halogen in chemical substances.

Complete step by step answer:
In the Carius method, a known mass of the compound is heated with concentrated nitric acid in the presence of silver nitrate in a hard glass tube. The hard glass tube is known as Carius tube. Carbon dioxide and water are formed by the oxidation of carbon and hydrogen respectively. Corresponding AgX is formed by the halogen. We have to filter, dry and weight it.
We can calculate the percentage of X using the formula,

Percentage of X$= \dfrac{{\left( {{\text{Atomic mass of X}}} \right)}}{{{\text{Molecular mass of AgX}}}} \times \dfrac{{\left( {{\text{Mass of AgX}}} \right)}}{{{\text{Mass of compound}}}} \times 100$
Estimation of sulfur by Carius method:
We have to take a known mass of the compound and heat it with concentrated nitric acid in the presence of a solution of barium chloride in the Carius tube. Sulfuric acid is formed by the oxidation of sulfur and Barium sulfate is obtained as precipitate when we add extra barium chloride. We then dry and weigh barium sulfate.
We can calculate the percentage of sulfur using the formula,
Percentage of sulfur$= \dfrac{{\left( {{\text{Atomic mass of S}}} \right)}}{{{\text{Molecular mass of BaS}}{{\text{O}}_4}}} \times \dfrac{{\left( {{\text{Mass of BaS}}{{\text{O}}_4}} \right)}}{{{\text{Mass of compound}}}} \times 100$
The quantity of sulfur obtained by Carius method is estimated by Barium sulfate $\left( {BaS{O_4}} \right)$.

Therefore, the option (C) is correct.

Note:
The need for adding the nitric acid is to oxidize carbon and hydrogen. Concentrated nitric acid oxidizes iodine to iodic acid and doesn't show any other halogens. Even the oxidation of iodine by concentrated nitric acid occurs at higher temperatures only.