Understanding Bleaching Powder Manufacturing

Bleaching powder, also known as Calcium Hypochlorite ($\text{CaOCl}_2$), is a chemical compound widely used as a bleaching agent and disinfectant. Its manufacturing process involves reacting a specific gas with dry slaked lime.

The Role of Chlorine Gas in Bleaching Powder Production

The industrial production of bleaching powder primarily involves the reaction between dry calcium hydroxide, commonly known as slaked lime ($\text{Ca(OH)}_2$), and chlorine gas ($\text{Cl}_2$). When chlorine gas is passed over dry slaked lime, a chemical reaction occurs, producing bleaching powder and water.

The chemical equation representing this reaction is:

$\text{Ca(OH)}_2\text{(s)} + \text{Cl}_2\text{(g)} \rightarrow \text{CaOCl}_2\text{(s)} + \text{H}_2\text{O(l)}$

This equation shows that chlorine gas is a necessary reactant in the manufacturing process of bleaching powder. Therefore, chlorine gas is the gas used for this purpose.

Why Other Gases Are Not Used

Let's consider the other options provided:

• Nitrogen ($\text{N}_2$): Nitrogen is a very unreactive gas at room temperature. It does not react with slaked lime to form bleaching powder or any similar compound with bleaching properties.
• Sulphur ($\text{S}$): Sulphur is a solid element, not a gas under normal conditions. While sulphur compounds like sulphur dioxide ($\text{SO}_2$) can act as reducing bleaching agents (different mechanism from oxidative bleaching like chlorine), elemental sulphur gas is not involved in the manufacturing of bleaching powder ($\text{CaOCl}_2$).
• Oxygen ($\text{O}_2$): Oxygen is essential for many processes, but it does not react directly with slaked lime in a way that produces bleaching powder. Bleaching powder's oxidative properties come from the hypochlorite ion ($\text{OCl}^-$) derived from chlorine.

Based on the chemical process, chlorine gas is uniquely used for manufacturing bleaching powder by reacting with slaked lime.

Revision Table: Gases and Their Uses

Additional Information on Bleaching Powder

Bleaching powder is technically a mixture containing calcium hypochlorite ($\text{Ca(OCl)}_2$), calcium chloride ($\text{CaCl}_2$), and calcium hydroxide ($\text{Ca(OH)}_2$). Its active component is calcium hypochlorite.

• How it works: When bleaching powder reacts with water, it produces hypochlorous acid ($\text{HOCl}$), which is a powerful oxidizing agent responsible for its bleaching and disinfecting actions.
• Applications: Besides bleaching cotton and linen in the textile industry, it is widely used for disinfecting drinking water supplies and swimming pools. It is also used as an oxidizing agent in many chemical industries.
• Storage: Bleaching powder should be stored in a cool, dry place in airtight containers because it reacts with moisture and carbon dioxide from the air, losing its chlorine content and thus its effectiveness.