Question

For testing sodium carbonate solution for the presence of sulphate ions as impurities, one should add:
A. excess hydrochloric acid and silver nitrate solution.
B. excess sulphuric acid and silver nitrate solution.
C. excess nitric acid and silver nitrate solution.
D. excess hydrochloric acid and barium chloride solution.

Answer 1

Hint: For the testing of sodium carbonate solution for the presence of sulfate ions as impurities, one should add an excess hydrochloric acid and barium chloride solution. When the sodium carbonate reacts with HCl, it forms sodium chloride and then the barium chloride reacts with the sulphate impurities later.

Complete step by step answer:
When sodium carbonate reacts with an excess of hydrochloric acid, it gets neutralized and the following reaction takes place:
$N{a_2}C{O_3} + 2HCl \to 2NaCl + {H_2}O + C{O_2}$
The products formed in the above reaction are sodium chloride, water and carbon dioxide.
In the next step, we find that the barium chloride solution reacts with the sulphur impurities to give the following reaction:
$BaC{l_2} + SO_4^{2 - } \to BaS{O_4} \downarrow + 2C{l^ - }$
In this reaction, a white precipitate is formed. This white precipitate formed is the barium sulphate along with chloride ions. The white precipitate formation is an indication of the presence of sulphate ions in the solution as impurities.
Thus, the correct option is D i.e excess hydrochloric acid and barium chloride solution.

Note:
The addition of barium chloride to the solution containing sulphates as an impurity is used as an indication test for the presence of sulphate ions in a solution.