Introduction:
The preparation of sodium thiosulphate (Na2S2O3) involves boiling sodium sulphite (Na2SO3) solution with sulphur (S) in an alkaline medium. This process is necessary to ensure the successful formation of sodium thiosulphate. Using an acidic medium instead of an alkaline medium would not yield the desired product. This can be explained in detail as follows:

1. Reaction Mechanism:
The reaction involved in the preparation of sodium thiosulphate can be represented as follows:
Na2SO3 + S + 2NaOH → Na2S2O3 + H2O

2. Role of Alkaline Medium:
The alkaline medium, provided by sodium hydroxide (NaOH), plays a crucial role in this reaction. It serves the following purposes:
- Alkaline conditions facilitate the dissolution of sulphur (S) and sodium sulphite (Na2SO3).
- Sodium hydroxide acts as a catalyst, accelerating the reaction rate.
- It helps maintain the pH of the reaction mixture, preventing the formation of undesired by-products.

3. Acidic Medium:
Using an acidic medium instead of an alkaline medium would affect the reaction in several ways:
- Acidic conditions would hinder the dissolution of sulphur (S) and sodium sulphite (Na2SO3).
- Acidic environments would promote the formation of undesired by-products or side reactions.
- The presence of acid would likely decompose sodium thiosulphate into sodium sulphite and sulphur dioxide, resulting in a loss of the desired product.

4. Formation of Sodium Thiosulphate:
In an alkaline medium, sodium thiosulphate is formed through a series of reactions. Sodium sulphite reacts with sulphur to form sodium thiosulphate, while water is produced as a by-product. The alkaline conditions help drive this reaction forward.

5. Importance of Boiling:
Boiling the reaction mixture is essential to accelerate the reaction rate and ensure complete conversion of reactants to products. It helps overcome energy barriers and increases the collision frequency between reactant particles, leading to a more efficient reaction.

Conclusion:
In conclusion, the preparation of sodium thiosulphate requires boiling a sodium sulphite solution with sulphur in an alkaline medium. The alkaline conditions provided by sodium hydroxide are crucial for the successful formation of sodium thiosulphate. Using an acidic medium would hinder the reaction, promote side reactions, and result in the loss of the desired product. Boiling the mixture helps to enhance the reaction rate and ensure complete conversion of reactants to products.

I think in acidic medium Sodium will form NaH
and we will not get Na2S2O3