Chemistry in Everyday Life (Class 12): Drugs, Detergents and Food Chemistry
A high-scoring chapter that students under-prepare because it looks like general knowledge. It is mostly classification, and classification is learnable.
How drugs are classified
| Basis | What it groups by | Useful for |
|---|---|---|
| Pharmacological effect | The effect produced — analgesic, antipyretic | Choosing a treatment for a symptom |
| Drug action | The biochemical process affected | Understanding mechanism |
| Chemical structure | Shared structural features | Predicting similar activity |
| Molecular target | The enzyme or receptor acted on | Designing selective drugs |
Questions frequently ask which classification is most useful for a stated purpose, so learn what each is for rather than only its name.
Enzyme inhibitors and receptors
Many drugs work by inhibiting an enzyme. A competitive inhibitor resembles the substrate closely enough to occupy the active site, blocking the real substrate. A non-competitive inhibitor binds elsewhere and changes the enzyme's shape so the active site no longer functions.
Other drugs act at receptors, which are proteins in cell membranes that receive chemical messages. A drug that blocks the receptor prevents the natural messenger binding, which is how many medicines produce their effect.
The main therapeutic classes
- Antacids neutralise excess stomach acid. Simple metal hydroxides act chemically; later drugs instead suppress acid production by blocking the receptor that triggers it — a more effective approach because it treats the cause rather than the symptom.
- Antihistamines block histamine receptors and so relieve allergic symptoms.
- Tranquillisers act on the central nervous system and treat stress and anxiety.
- Analgesics relieve pain. Non-narcotic types do not cause dependence; narcotic types relieve severe pain but are addictive and tightly regulated.
- Antimicrobials destroy or inhibit microorganisms, and include antibiotics, antiseptics and disinfectants.
Antibiotics: bactericidal versus bacteriostatic
Bactericidal antibiotics kill bacteria; bacteriostatic ones inhibit their growth so the body's defences can clear them. Antibiotics are also described as broad spectrum, effective against many types, or narrow spectrum, effective against a limited range. Both distinctions are commonly asked.
Antiseptics and disinfectants
Soaps and detergents
Both clean because their molecules have a long hydrocarbon tail that dissolves in grease and an ionic head that dissolves in water. In water they form micelles — spherical clusters with tails inward trapping the grease and heads outward facing the water — so the dirt is carried away.
| Soaps | Synthetic detergents | |
|---|---|---|
| Made from | Alkali hydrolysis of fats and oils | Petrochemical feedstocks |
| In hard water | Form insoluble scum with Ca and Mg | Salts remain soluble, so they work |
| In acidic water | Ineffective — converted to the free acid | Still effective |
| Biodegradability | Readily biodegradable | Branched-chain types degrade poorly |
The hard-water behaviour is the key comparison, and the branched-chain biodegradability problem is the standard environmental question — straight-chain detergents were introduced precisely to fix it.
Food chemistry
- Preservatives prevent spoilage by microorganisms.
- Antioxidants prevent oxidation, particularly of fats, which is what causes rancidity.
- Artificial sweeteners provide sweetness without food value, which matters for people who must restrict sugar intake. Their stability to heat differs, so some are unsuitable for cooking — a frequently asked comparison.
Frequently asked questions
What is the difference between a medicine and a drug?
A drug is any chemical that affects a biological process. It becomes a medicine when used at a therapeutic dose to treat disease. Above that dose the same substance may be a poison, which is why dosage is central.
Why do soaps fail in hard water?
Calcium and magnesium ions form insoluble salts with the fatty acid anions, producing scum instead of lather. Detergent salts of the same ions remain soluble, so cleaning continues.
Can one compound be both an antiseptic and a disinfectant?
Yes, at different concentrations. Dilute solutions may be safe on skin while concentrated ones are used on surfaces.
Why are broad-spectrum antibiotics not always preferable?
Because they also destroy beneficial bacteria and accelerate the development of resistance. A narrow-spectrum antibiotic is preferred where the organism is known.
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