Question

Sodium thiosulphate is prepared by (a) reducing Na₂SO₄ solution with H₂S(b) boiling Na₂SO₃ solution with S in alkaline medium(c) neutralising H₂S₂O₃ solution with NaOH(d) boiling Na₂SO₃ solution with S in acidic medium

Answer 1

There is a three-step procedure for the production of sodium thiosulfate involving three separate chemical reactions. The first reaction starts with sodium carbonate, sulfur dioxide, and water.

Step 1:

Na2 CO3 + 2SO2 + H2 O → 2NaHSO3 + CO2

Sodium carbonate reacts with sulfur dioxide and water to produce sodium bisulfite and carbon dioxide. To do this, we dissolve sodium carbonate in water and bubble sulfur dioxide into the solution. Large white bubbles will be seen, which is a result of the carbon dioxide gas escaping the solution.

Step 2:

2NaHSO3 + Na2 CO3 → 2Na2 SO3 + CO2 + H2 O

This reaction might seem strange because we started the three-reaction process with sodium carbonate, and now we are adding sodium carbonate to the product of the first reaction! That is how chemistry works sometimes. This combination is boiled for around 15 minutes and sodium sulfite remains in solution with water while the carbon dioxide escapes.

Step 3:

Na2 SO3 + S → 2Na2 S2 O3

The last step in preparing sodium thiosulfate requires the addition of sulfur that is wetted slightly with ethanol. This solution is boiled in a closed system so that the water that evaporates condenses and drips back into the solution. After the boiling process, the resulting solution is filtered. This separates the remaining solid sulfur from the sodium thiosulfate solution.

I hope this help to you....