Chemistry in Daily Life: Dyes, Drugs, Cleansing Agents, Food Chemistry

Chemistry in the Service of Mankind: Unit 18 Notes

1. Synthetic Dyes

What are synthetic dyes?

Synthetic dyes are colored compounds artificially prepared to add color to fabrics, cosmetics, and food. They replace natural dyes (e.g., indigo, turmeric) because they are cheaper, brighter, and more stable.

How are they made?

Most synthetic dyes are derived from aromatic compounds (benzene rings) and contain chromophores (groups like –NO₂, –N=N–, –COOH) that absorb light and reflect color.

Types of Synthetic Dyes

mindmap
  root((Synthetic Dyes))
    Azo Dyes
      "–N=N– group, bright colors (orange, red)"
      Example: Methyl orange
    Triphenylmethane Dyes
      "Phosphorus, used in inks and cosmetics"
      Example: Malachite green
    Anthraquinone Dyes
      "Fast to light, used in fabrics"
      Example: Alizarin
    Indigoid Dyes
      "Blue dye, used in jeans"
      Example: Indigo

Advantages & Disadvantages

Example: Preparation of Methyl Orange (Azo Dye)

1. Reactants: Sulfanilic acid + NaNO₂ + HCl → Diazonium salt
2. Coupling: Diazonium salt + N,N-dimethylaniline → Methyl orange (orange-red dye)

2. Medicinal Chemistry (Drugs)

What are drugs?

Drugs are chemical substances that affect the body’s functions. They can be:

• Natural (e.g., morphine from opium)
• Semi-synthetic (e.g., penicillin derivatives)
• Synthetic (e.g., aspirin, paracetamol)

How do drugs work?

Drugs interact with receptors in the body (like a lock-and-key mechanism). Some block harmful molecules, while others stimulate healing.

Types of Drugs

mindmap
  root((Drugs))
    Analgesics
      "Pain relievers (aspirin, paracetamol)"
    Antibiotics
      "Kill bacteria (penicillin, tetracycline)"
    Antiseptics
      "Prevent infection (iodine, Dettol)"
    Antacids
      "Neutralize stomach acid (milk of magnesia)"
    Antipyretics
      "Reduce fever (aspirin, ibuprofen)"

Example: Aspirin (Acetylsalicylic Acid)

• Structure: Contains a benzene ring + COOH group.
• Action: Blocks prostaglandins (chemicals that cause pain and inflammation).
• Preparation:

  flowchart TD
    A["Salicylic acid"] -->|"+ Acetic anhydride"| B["Aspirin"]
    B -->|"Hydrolysis"| C["Salicylic acid + Acetic acid"]

3. Cleansing Agents (Soaps & Detergents)

What are soaps and detergents?

• Soaps: Sodium/potassium salts of fatty acids (e.g., sodium stearate).
• Detergents: Synthetic sodium alkylbenzenesulfonates (better in hard water).

How do they work?

They lower surface tension and emulsify oils/grease so water can wash them away.

Comparison: Soaps vs. Detergents

Example: Saponification (Soap Making)

1. Reactants: Triglycerides (fat) + NaOH → Glycerol + Soap
2. Equation:

(C₁₇H₃₅COO)₃C₃H₅ + 3NaOH → 3C₁₇H₃₅COONa + C₃H₅(OH)₃

4. Food Chemistry (Preservatives & Artificial Sweeteners)

Why are additives used?

• Preservatives (e.g., sodium benzoate) prevent spoilage.
• Artificial sweeteners (e.g., saccharin, aspartame) are calorie-free alternatives to sugar.

Common Food Additives

mindmap
  root((Food Additives))
    Preservatives
      "Sodium benzoate, sulfur dioxide"
    Artificial Sweeteners
      "Aspartame, saccharin, sucralose"
    Flavors & Colors
      "Tartrazine (yellow dye), vanillin"
    Antioxidants
      "BHA, BHT (prevent rancidity)"

Example: Saccharin (Artificial Sweetener)

• Structure: Contains a benzene ring + SO₂NH group.
• Sweetness: 300–400 times sweeter than sugar but no calories.
• Disadvantage: Linked to cancer in high doses (controversial).

5. Water Purification (Chemistry Behind It)

How is water purified?

1. Coagulation: Al₂(SO₄)₃ adds to remove dirt.
2. Sedimentation: Particles settle.
3. Filtration: Sand/charcoal removes microbes.
4. Chlorination: Cl₂ kills bacteria.

Chemical Reactions in Water Treatment

• Chlorination:

  Cl₂ + H₂O → HCl + HClO (hypochlorous acid, kills germs)
  

• Fluoridation (for dental health):

  NaF → F⁻ (fluoride ions in water)
  

Exam Tip: How to Score Full Marks in Unit 18

1. Memorize key reactions (e.g., soap making, aspirin synthesis).
2. Compare soaps vs. detergents in tables (NEB loves this!).
3. Draw structures of dyes (azo, triphenylmethane) and drugs (aspirin, saccharin).
4. Explain applications (e.g., why detergents are better in hard water).
5. Practice short-answer questions on food additives and water purification.

NEB Board-Style Questions (Practice These!)

Short Answer (3 marks each)

1. Explain the difference between synthetic dyes and natural dyes with one example each.
2. How is aspirin prepared from salicylic acid? Write the reaction.
3. Why do soaps not work well in hard water? Explain with a chemical equation.
4. What are artificial sweeteners? Give one example and its disadvantage.

Long Answer (5–7 marks)

5. Describe the process of water purification with chemical reactions involved.
6. Compare soaps and detergents in a table. Which one would you use in hard water and why?
7. Explain the structure and uses of azo dyes. How is methyl orange prepared?

Final Advice:

• Draw diagrams for reactions (e.g., soap making, dye synthesis).
• Use real-life examples (e.g., "Dettol is an antiseptic").
• Revise key terms (chromophore, saponification, emulsification).

Good luck for your NEB exam! 🚀