What is the difference between a soap and a synthetic detergent?

Soaps are sodium or potassium salts of long-chain fatty acids. They do not work in hard water (form scum with Ca²⁺/Mg²⁺). Synthetic detergents are sodium salts of sulphonic acids. They work in hard water and acidic conditions, and are more soluble. They are non-biodegradable (linear alkylbenzene sulphonates are now used to improve biodegradability).

What are polymers? Distinguish between addition and condensation polymers.

Polymers are large macromolecules made of repeating monomer units. Addition polymers form by repeated addition of monomers with no byproduct (e.g., polythene from ethylene). Condensation polymers form when monomers react with elimination of small molecules like H₂O (e.g., nylon-6,6 from hexamethylenediamine and adipic acid).

Tamil Nadu Class 12 Chemistry in Everyday Life — Samacheer Kalvi

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Quick Summary

This chapter links chemistry to real-world applications. It carries 6–8 marks in TN HSE and is easy to score. Focus on drug classification, soap and detergent chemistry, and polymer types.

Drugs and Medicines

Classification by Pharmacological Effect

Class	Action	Examples
Analgesics	Relieve pain	Aspirin, Paracetamol, Morphine
Antipyretics	Reduce fever	Aspirin, Paracetamol
Antiseptics	Kill/inhibit microbes on living tissue	Dettol, Savlon, Iodine tincture
Disinfectants	Kill microbes on non-living surfaces	1% phenol, Chlorine, Lysol
Antibiotics	Kill/inhibit bacteria	Penicillin, Streptomycin, Tetracycline
Antihistamines	Block histamine (allergy)	Benadryl (diphenhydramine)
Tranquilisers	Treat anxiety/mental illness	Valium (diazepam), Meprobamate
Antacids	Neutralise stomach acid	NaHCO₃, Mg(OH)₂, Al(OH)₃

Aspirin (Acetylsalicylic acid):

Acts as analgesic, antipyretic, and anti-inflammatory
Inhibits prostaglandin synthesis
Used to prevent blood clotting (anticoagulant at low dose)

Penicillin: First antibiotic; bactericidal; inhibits cell wall synthesis in bacteria

Food Additives

Type	Purpose	Examples
Preservatives	Prevent microbial growth	NaCl, Sugar, Vinegar, Benzoic acid, Sodium benzoate
Antioxidants	Prevent oxidation (rancidity)	BHA, BHT, Vitamin C, Vitamin E
Artificial sweeteners	Sweet taste without calories	Saccharin, Aspartame, Sucralose
Food colours	Appearance	Tartrazine (yellow), Erythrosine (red)

Saccharin: First synthetic sweetener; 550× sweeter than sucrose; not metabolised; used by diabetics

Soaps and Detergents

Soap making (Saponification):

Fat/oil + NaOH → Soap + Glycerol
Soap = sodium salt of fatty acid (e.g., C₁₇H₃₅COONa — sodium stearate)

How soap cleans (micelle formation): 1. Soap has hydrophilic head (–COO⁻Na⁺) and hydrophobic tail (long hydrocarbon chain) 2. Hydrophobic tails surround the oily dirt; hydrophilic heads face water → micelle 3. Micelle is rinsed away with water

Hardness problem: Ca²⁺/Mg²⁺ ions react with soap → insoluble scum → soap ineffective in hard water

Synthetic Detergents:

Anionic: CH₃(CH₂)₁₁C₆H₄SO₃⁻Na⁺ (sodium alkylbenzene sulphonate)
Cationic: Quaternary ammonium salts (also antiseptic)
Non-ionic: polyethylene glycol derivatives

Polymers

Classification

Basis	Types	Examples
Source	Natural	Rubber, Starch, Cellulose
Source	Synthetic	PVC, Polythene, Nylon
Structure	Linear	HDPE, PVC
Structure	Branched	LDPE
Structure	Cross-linked	Bakelite, Melamine
Reaction type	Addition polymer	Polythene, PVC, Polystyrene, PTFE
Reaction type	Condensation polymer	Nylon-6,6; Dacron; Bakelite

Important Polymers

Polymer	Monomer(s)	Uses
Polythene (HDPE/LDPE)	Ethylene	Bags, bottles, pipes
PVC	Vinyl chloride	Pipes, insulation
Teflon (PTFE)	Tetrafluoroethylene	Non-stick cookware
Nylon-6,6	Hexamethylenediamine + Adipic acid	Ropes, clothes, toothbrush bristles
Nylon-6	Caprolactam	Fabrics
Dacron (Terylene)	Ethylene glycol + Terephthalic acid	Clothing, bottles (PET)
Bakelite	Phenol + Formaldehyde	Electrical switches, handles
Natural rubber	Isoprene (2-methylbutadiene)	Tyres, gloves

Vulcanisation of rubber: Heating natural rubber with sulphur → cross-links → harder, less sticky rubber

Important Questions

One Mark

1. Name a non-narcotic analgesic. 2. What is saponification? 3. Name the monomer of Teflon. 4. Define an antiseptic. 5. What is an antacid? Give one example.

Short Answer (3 marks)

1. How do soaps cleanse oily dirt? Explain using micelle structure. 2. Distinguish between soaps and synthetic detergents. 3. Classify polymers based on the type of polymerisation reaction with examples.

Long Answer (5 marks)

1. Classify drugs based on pharmacological effects with examples and their uses. 2. Describe the structure and preparation of Nylon-6,6 and Dacron. Compare addition and condensation polymerisation.

Board Exam Tips

Difference between antiseptic and disinfectant: same chemical (phenol) at different concentrations
Aspirin is both analgesic AND antipyretic — give both in exam
Biodegradable vs non-biodegradable detergents — recent environmental question
Bakelite is thermosetting (cannot be remoulded); Polythene is thermoplastic

Revision Checklist

[ ] Drug classification with two examples each
[ ] Aspirin — all actions
[ ] Saponification reaction
[ ] Micelle formation diagram
[ ] Difference between soaps and detergents
[ ] Addition vs condensation polymers
[ ] Important polymers, monomers, and uses table

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Frequently Asked Questions

Analgesics are drugs that relieve pain without causing loss of consciousness. They are of two types: (1) Non-narcotic analgesics like aspirin and paracetamol, which are used for mild pain. (2) Narcotic analgesics like morphine and codeine, which are used for severe pain but are habit-forming.