Question

Sodium thiosulphate reacts with $dil.HCl$ to form $NaCl$ , ${H_2}O$ , $X$ and $Y$ . $X$ reacts with $N{a_2}S$ to form $N{a_2}{S_2}{O_3}$ and $Y$ . Which of the following is $Y$ ?
A. $S{O_2}$
B. ${H_2}S{0_4}$
C. $S$
D. ${H_2}S$

Answer 1

Sodium thiosulphate reacts with $dil.HCl$ to form $NaCl$ , water, sulphur dioxide and sulphur. Sodium thiosulphate is an inorganic compound having formula $N{a_2}{S_2}{O_3}.x{H_2}O$ . Generally it is of white color or colorless pentahydrate and it is an efflorescent crystalline solid that dissolves well in water and loses water readily.

Complete step-by-step answer: As, Sodium thiosulphate reacts with $dil.HCl$ to form $NaCl$ , water, sulphur dioxide and sulphur.
The reaction can be given by:
$N{a_2}{S_2}{O_3} + HCl \to 2NaCl + {H_2}O + S{O_2} + S$
Now, when Sulphur dioxide reacts with sodium sulphide to form sodium thiosulphate and sulphur.
The reaction is given as:
$3S{O_2} + 2N{a_2}S \to 2N{a_2}{S_2}{O_3} + S$
Hence, $Y$ is sulphur.

Additional Information:
Uses of Sodium thiosulphate:
1. Gold mining
2. Water treatment
3. Analytical Chemistry
4. the development of silver-based photographic film and prints, and medicine.
Now, In iodometry (Analytical Chemistry):
In analytical chemistry, sodium thiosulphate is used because during the reaction (iodometry titration) the thiosulfate anion reacts stoichiometrically with iodine in aqueous solution, and reduced it to iodide and thiosulfate is oxidized to tetrathionate.
Because of this quantitative nature of the reaction and an excellent shelf-life, it is used as a titrant in iodometry titration. Sodium thiosulphate is also a component of iodine clock experiments.

So, the correct option is C.

Note: This setup can be used to measure the oxygen content of water through a long series of reactions in the Winkler test that is used for dissolved oxygen. It is also used in estimating the concentrations of certain compounds in solution (hydrogen peroxide, for instance) volumetrically that is quantitatively and also in estimating the chlorine content in commercial bleaching powder and water.