Bleaching Powder

2. Bleaching Powder (CaOCl2): Bleaching powder is also known as chloride of lime. It is a solid and yellowish white in colour. Bleaching powder can be easily identified by the strong smell of chlorine. When calcium hydroxide (slaked lime) reacts with chlorine, it gives calcium oxychloride (bleaching powder) and water is formed. Acids Bases and Salts Class 10 Notes Science Chapter 2 32 Aqueous solution of bleaching powder is basic in nature. The term bleach means removal of colour. Bleaching powder is often used as bleaching agent. It works because of oxidation. Chlorine in the bleaching powder is responsible for bleaching effect. Use of Bleaching Powder: Bleaching powder is used as disinfectant to clean water, moss remover, weed killers, etc. Bleaching powder is used for bleaching of cotton in textile industry, bleaching of wood pulp in paper industry. Bleaching powder is used as oxidizing agent in many industries, such as textiles industry, paper industry, etc. 3. Baking Soda (NaHCO3): Baking soda is another important product which can be obtained using byproducts of chlor – alkali process. The chemical name of baking soda is sodium hydrogen carbonate (NaHCO3) or sodium bicarbonate. Bread soda, cooking soda, bicarbonate of soda, sodium bicarb, bicarb of soda or simply bicarb, etc. are some other names of baking soda. Preparation Method: Baking soda is obtained by the reaction of brine with carbon dioxide and ammonia. This is known as Solvay process. Acids Bases and Salts Class 10 Notes Science Chapter 2 33 In this process, calcium carbonate is used as the source of CO2 and the resultant calcium oxide is used to recover ammonia from ammonium chloride. Properties of Sodium Bicarbonate: Sodium bicarbonate is white crystalline solid, but it appears as fine powder. Sodium hydrogen carbonate is amphoteric in nature. Sodium hydrogen carbonate is sparingly soluble in water. Thermal decomposition of sodium hydrogen carbonate (baking soda). When baking soda is heated, it decomposes into sodium carbonate, carbon dioxide and water. 2NaHCO3 + heat → Na2CO3 + CO2 + H2O Sodium carbonate formed after thermal decomposition of sodium hydrogen carbonate decomposes into sodium oxide and carbon dioxide on further heating. Na2CO3 → Na2O + CO2 This reaction is known as Dehydration reaction. Use of Baking Soda: Baking soda is used in making of baking powder, which is used in cooking as it produces carbon dioxide which makes the batter soft and spongy. Baking soda is used as an antacid. Baking soda is used in toothpaste which makes the teeth white and plaque free. Baking soda is used in cleansing of ornaments made of silver. Since sodium hydrogen carbonate gives carbon dioxide and sodium oxide on strong heating, thus, it, is used as a fire extinguisher. Baking Powder: Baking powder produces carbon dioxide on heating, so it is used in cooking to make the batter spongy. Although, baking soda also produces carbon dioxide on heating, but it is not used in cooking because on heating, baking soda produces sodium carbonate along with carbon dioxide. The sodium carbonate, thus, produced, makes the taste bitter. Acids Bases and Salts Class 10 Notes Science Chapter 2 34 Baking powder is the mixture of baking soda and a mild edible acid. Generally, tartaric acid is mixed with baking soda to make baking powder. Acids Bases and Salts Class 10 Notes Science Chapter 2 35 When baking powder is heated, sodium hydrogen carbonate (NaHCO3) decomposes to give CO2 and sodium carbonate (Na2CO3). CO2 causes bread and cake fluffy. Tartaric acid helps to remove bitter taste due to formation of Na2CO3. 4. Washing Soda (Sodium Carbonate) Preparation Method: Sodium carbonate is manufactured by the thermal decomposition of sodium hydrogen carbonate obtained by Solvay process. Acids Bases and Salts Class 10 Notes Science Chapter 2 36 The sodium carbonate obtained in this process is dry. It is called Soda ash or Anhydrous sodium carbonate. Washing soda is obtained by rehydration of anhydrous sodium carbonate. Acids Bases and Salts Class 10 Notes Science Chapter 2 37 Since there are 10 water molecules in washing soda, hence, it is known as Sodium Bicarbonate Decahydrate. Sodium carbonate is a crystalline solid and it is soluble in water when most of the carbonates are insoluble in water. Use of sodium carbonate: It is used in the cleaning of cloths, especially in rural areas. In the making of detergent cake and powder. In removing the permanent hardness of water. It is used in glass and paper industries. The water of Crystallization: Many salts contain water molecule and are known as Hydrated Salts. The water molecule present in salt is known as Water of crystallization. Examples: Copper sulphate pentahydrate (CuSO4.5H2O): Blue colour of copper sulphate is due to presence of 5 molecules of water. When copper sulphate is heated, it loses water molecules and turns: into grey – white colour, which is known as anhydrous copper sulphate. After adding water, anhydrous copper sulphate becomes blue again. Acids Bases and Salts Class 10 Notes Science Chapter 2 38