What is used to make drinking water free from germs?

Question

Examoogle · Accepted Answer

The correct answer is Option D: Bleaching powder. Bleaching powder (chemical name: calcium oxychloride, $CaOCl_2$) is a pale yellowish-white powder that releases chlorine gas when dissolved in water. This released chlorine acts as a powerful oxidizing agent and disinfectant, effectively killing harmful germs, bacteria, and microorganisms in drinking water.

Step-by-Step Solution & Concepts:
Bleaching powder (chemical name: calcium oxychloride, $CaOCl_2$) is a pale yellowish-white powder that releases chlorine gas when dissolved in water. This released chlorine acts as a powerful oxidizing agent and disinfectant, effectively killing harmful germs, bacteria, and microorganisms in drinking water.

Working Principle: When bleaching powder is added to water, it reacts with water or dissolved carbon dioxide to release active chlorine ($Cl_2$). Chlorine is a potent disinfectant that disrupts the cell walls and metabolic enzymes of pathogens, rendering them inactive and making the water safe for drinking.

Key Formulas: $CaOCl_2 + H_2O \rightarrow Ca(OH)_2 + Cl_2$ — Reaction of bleaching powder with water; $Cl_2 + H_2O \rightarrow HCl + HOCl$ — Formation of hypochlorous acid for disinfection

Key Points: Bleaching powder is chemically known as Calcium oxychloride ($CaOCl_2$).; It acts as a disinfectant by releasing chlorine gas, which kills disease-causing bacteria and germs in water.; Washing soda ($Na_2CO_3 \cdot 10H_2O$) is used for removing permanent hardness of water.; Baking soda ($NaHCO_3$) is a mild, non-corrosive basic salt used in cooking and antacids.

Advantages: Cost-effective and easy to store/transport.; Highly efficient in killing bacteria, viruses, and pathogens in municipal water supplies.

Disadvantages: Over-dosing can leave an unpleasant taste and odor in water.; Does not remove dissolved heavy metals or suspended impurities by itself.

Applications: Municipal drinking water treatment plants; Sanitizing swimming pools and sewage systems; Bleaching cotton, linen, and wood pulp in industries

Additional Info: Option A (Washing soda): Used for softening hard water, not for killing germs.. Option B (Sodium hydroxide): A strong alkali (caustic soda) used in soap and paper manufacturing, highly corrosive and unsafe for direct drinking water treatment.. Option C (Baking soda): Used as an antacid and baking agent, lacks germicidal disinfecting properties.

Answer: D is correct — Bleaching powder is used as a disinfectant to make drinking water free from germs by releasing chlorine.

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