12.2 Chemistry for Cleanliness

Maintaining cleanliness plays a vital role in good health. Several chemicals and cleaning agents help in cleaning our body, clothes, toilets, and other household items. Below are the key substances and their uses:

1. Washing Soda

• Chemical Name: Sodium Carbonate Decahydrate (Na₂CO₃·10H₂O).

• Preparation:

• When carbon dioxide (CO₂) reacts with sodium hydroxide (NaOH), it forms sodium carbonate (Na₂CO₃).

• Sodium carbonate dissolves in water, and 10 water molecules combine to form washing soda.

• Reaction:

• 2NaOH + CO₂ → Na₂CO₃ + H₂O

• Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O

• Uses: Primarily used for washing clothes.

2. Toilet Cleaner

• Main Ingredients: Sodium hydroxide (NaOH) and Sodium hypochlorite (NaOCl).

• Mechanism:

• Sodium hydroxide reacts with oils and proteins in toilets, while sodium hypochlorite releases nascent oxygen (O) which breaks down colorants and kills germs.

• Reaction:

• NaOCl + H₂O → HOCl + [O]

• Colourful substances become colorless, and germs are destroyed by nascent oxygen.

3. Soap

• Chemical Nature: Soap is the sodium or potassium salt of higher fatty acids (e.g., Sodium Stearate: C₁₇H₃₅COONa).

• Preparation: Soap is created through a process called saponification, where fats or oils react with sodium hydroxide (NaOH) or potassium hydroxide (KOH) to produce soap and glycerine.

• Types of Soap:

• Toilet Soap: Used for cleaning skin.

• Laundry Soap: Used for washing clothes.

• Saponification Reaction:

• Oil/Fat + Alkali → Soap + Glycerine.

• Fatty Acids:

• Stearic acid (from animal fat) is a saturated fatty acid (no C=C bonds).

• Oleic acid (from olive oil) is an unsaturated fatty acid (contains C=C bonds).

4. Detergents

• Chemical Composition: Detergents are made by reacting lauryl alcohol (C₁₂H₂₅OH) with sulfuric acid (H₂SO₄), then neutralizing with sodium hydroxide (NaOH) to produce sodium lauryl sulfate (C₁₂H₂₅SO₄Na).

• Cleaning Mechanism: Detergents, like soaps, remove oils and dirt. Their long hydrocarbon chains have a hydrophilic (water-attracting) head and a hydrophobic (water-repellent) tail, which help break down grease and dirt.

5. Differences Between Soap and Detergent

• Soap:

• Made from fatty acids and alkali (NaOH or KOH).

• Less effective in hard water.

• Detergent:

• Made from synthetic chemicals.

• Works well in hard water.

6. Bad Effects of Excessive Soap or Detergent Use

• Excess soap can reduce oxygen in water, harming aquatic life.

• Detergents can cause eutrophication, increasing plant growth and depleting oxygen in water, leading to the death of aquatic animals.

7. Toiletries Use and pH

• The pH of skin is between 4.8-5.5. Toiletries should have a pH that complements this to prevent skin damage and bacterial infections.

8. Bleaching Powder

• Chemical Name: Calcium Oxychloride (Ca(OCl)₂).

• Uses: Bleaching powder is used to remove stains from clothes and kill germs on floors and toilets.

• Reaction: When mixed with water, bleaching powder produces calcium chloride (CaCl₂) and hypochlorous acid (HOCl).

• Mechanism:

• HOCl releases nascent oxygen (O) that bleaches colored stains and kills germs.

• Reaction: Ca(OCl)₂ + H₂O → CaCl₂ + HOCl

• HOCl → HCl + [O] (nascent oxygen).

9. Glass Cleaner

• Composition: Often contains isopropyl alcohol (C₃H₇OH) and ammonium hydroxide (NH₄OH).

• Mechanism: Removes oils, grease, and organic stains from glass surfaces. Ammonium hydroxide dissolves oils, while alcohol removes organic residues.

10. Laboratory Production of Ammonia

• Ammonia (NH₃) can be prepared in the lab by heating ammonium chloride (NH₄Cl) with calcium oxide (CaO) or calcium hydroxide (Ca(OH)₂).

• Reaction:

• 2NH₄Cl + CaO → 2NH₃ + CaCl₂ + H₂O

• 2NH₄Cl + Ca(OH)₂ → 2NH₃ + CaCl₂ + 2H₂O

11. Industrial Production of Ammonia (Haber Process)

• Ammonia is produced industrially by mixing nitrogen (N₂) and hydrogen (H₂) in a 1:3 ratio, then heating at 450-550°C and 200-250 atm pressure with an iron catalyst.

• Reaction:

• N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + heat (92 kJ).

• The reaction is reversible, and ammonia is continuously produced while some nitrogen and hydrogen are reformed.