Question

Le-blanc process is employed in the manufacture of:
A) Baking soda
B) Washing soda
C) Potash
D) Plaster of paris

Answer 1

During Le-blanc process, an alkali metal chloride is used as a reactant. The end product is an alkali metal carbonate. In the first step, alkali metal reacts with sulphuric acid to form alkali sulphate and hydrogen chloride. In the next step, alkali metal sulphate reacts with carbon to form alkali metal sulphide and carbon dioxide.

Complete answer:
Baking soda is sodium bicarbonate, also known as sodium hydrogen carbonate. The chemical formula of baking soda is ${\text{NaHC}}{{\text{O}}_{\text{3}}}$ . To prepare baking soda, We can use the Solvay process. Washing soda is sodium carbonate. Its chemical formula is ${\text{N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$ . It is also prepared by the Solvay process.

Plaster of paris is calcium sulphate hemihydrate. Its chemical formula is ${\text{CaS}}{{\text{O}}_{\text{4}}} \cdot {{\text{H}}_2}{\text{O}}$ . We can prepare plaster of paris by heating gypsum so that it loses a part of water of hydration.

The Le-blanc process is an early industrial process. We can use this process to manufacture soda ash and potash. Soda ash is sodium carbonate. The chemical formula of soda ash is ${\text{N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$. Potash is potassium carbonate. The chemical formula of potash is ${{\text{K}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$. The Le-blanc process is employed in the manufacture of potash.

In the Le-blanc process, the reaction between sodium chloride and sulphuric acid gives sodium sulphate and hydrogen chloride. In the next step, sodium sulphate reacts with carbon to form sodium sulphide and carbon dioxide. In the last step, sodium sulphide reacts with calcium carbonate to form sodium carbonate and calcium sulphide. Similar set of reactions convert potassium chloride to potassium carbonate (potash).

Hence, the correct answer is option C.

Note: We can use potash as a mild drying agent. We can also use potash for softening of hard water. Potassium carbonate is an effective fire suppressant. The Leblanc process was an early industrial process for the production of soda ash.