Class 12 Chemistry in Everyday Life — Drugs, Food and Cleansing Agents
Chemistry in Everyday Life is the chapter students leave for the last night and then lose easy marks in. It has almost no reasoning — it is definitions, classifications and named examples — so it is entirely winnable if you organise it once instead of reading it five times. This guide sorts the chapter into the four groups that questions are actually built from, adds the numerical work that connects it to the rest of your syllabus, and flags the distinctions examiners test deliberately.
Before anything else, one caution. Every drug named in this chapter is syllabus content, not advice. Medicines must only ever be taken on the prescription of a qualified doctor, and nothing in a chemistry textbook is a reason to start, stop or change any treatment.
How drugs are classified
A drug is a low molar mass chemical (typically in the range of roughly 100–500 g/mol) that interacts with a biological target. There are four different classification schemes, and the question usually names which one it wants.
| Basis | What it groups by | Example grouping |
|---|---|---|
| Pharmacological effect | The effect produced, whatever the structure | All analgesics together, all antacids together |
| Drug action | The biochemical process it interferes with | Antihistamines — all block the action of histamine |
| Chemical structure | A shared structural feature | The sulpha drugs — all contain the sulphonamide group |
| Molecular target | The macromolecule it binds to | Enzyme inhibitors, receptor blockers |
Enzymes and receptors are the two targets. An enzyme inhibitor may be competitive — it resembles the substrate and blocks the active site — or it may bind at a different site and change the active site's shape so the substrate no longer fits. Receptors sit in the cell membrane and receive chemical messengers; an antagonist blocks the receptor's natural function, while an agonist mimics the natural messenger and switches the receptor on.
The therapeutic classes, with their examples
| Class | What it does | Named examples in the syllabus |
|---|---|---|
| Antacids | Reduce excess stomach acid | Sodium hydrogencarbonate, magnesium hydroxide, aluminium hydroxide; ranitidine and cimetidine block the histamine H₂ receptor; omeprazole and lansoprazole are proton pump inhibitors |
| Antihistamines | Block histamine at its receptor, relieving allergy symptoms | Brompheniramine, terfenadine |
| Tranquilizers | Act on the central nervous system; used for anxiety and sleep disorders | Barbiturates such as veronal and luminal; equanil; meprobamate; chlordiazepoxide |
| Analgesics — non-narcotic | Relieve pain without causing dependence | Aspirin, paracetamol |
| Analgesics — narcotic | Relieve severe pain; strictly controlled because of dependence | Morphine, codeine, heroin |
| Antimicrobials | Kill or stop micro-organisms | Antibiotics, antiseptics, disinfectants — see below |
| Antifertility drugs | Synthetic hormones that control fertility | Norethindrone (synthetic progesterone), ethynylestradiol (novestrol) |
A neat detail worth knowing: aspirin's antipyretic action lowers fever, and it is also known for an anti-blood-clotting effect. Paracetamol relieves pain and fever but does not act as an anti-inflammatory in the way aspirin does.
Antibiotic, antiseptic, disinfectant — the distinction that is always asked
| Term | Definition | Where it is applied | Examples |
|---|---|---|---|
| Antibiotic | Produced wholly or partly by a micro-organism; kills or inhibits other micro-organisms | Taken internally, on prescription | Penicillin, chloramphenicol, ofloxacin |
| Antiseptic | Kills or stops the growth of micro-organisms | On living tissue — wounds, cuts, skin | Dettol (chloroxylenol + terpineol), tincture of iodine (a 2–3% solution of iodine in alcohol–water), bithionol in soaps, 0.2% phenol solution |
| Disinfectant | Kills micro-organisms; too harsh for living tissue at the concentration used | On non-living surfaces — floors, drains, instruments | 1% phenol solution; chlorine at about 0.2–0.4 ppm in water; sulphur dioxide in low concentration |
Phenol is the classic exam trap. The same substance is an antiseptic at about 0.2% and a disinfectant at about 1%. What separates the two categories is not the chemical — it is the concentration and where it is applied.
Antibiotics are further split two ways. Bactericidal antibiotics kill bacteria (penicillin, ofloxacin, aminoglycosides), while bacteriostatic ones only stop them multiplying (erythromycin, tetracycline, chloramphenicol). Separately, penicillin is narrow spectrum — effective against a limited range of organisms — while chloramphenicol is broad spectrum. These are two independent classifications, so an antibiotic can be broad spectrum and bacteriostatic at the same time, and questions often combine them to see whether you have understood that.
Chemicals in food
Artificial sweeteners let a food taste sweet without adding carbohydrate energy, which matters for people who must control sugar intake. The sweetness figures below are the approximate values given in the textbook, quoted relative to cane sugar:
| Sweetener | Approx. sweetness vs sucrose | Point the exam asks about |
|---|---|---|
| Saccharin | About 550 times | The first popular artificial sweetener; passes through the body unchanged, so it adds no energy |
| Aspartame | About 100 times | Unstable at cooking temperature, so its use is limited to cold foods and soft drinks |
| Alitame | About 2000 times | So potent that controlling the sweetness of a food made with it is difficult |
| Sucralose | About 600 times | Stable at cooking temperature, so it can be used in baked foods |
Food preservatives stop spoilage by micro-organisms — sodium benzoate and the salts of sorbic and propanoic acids are the common ones, alongside plain table salt and sugar.
Antioxidants are more subtle: they are more reactive towards oxygen than the food is, so they are consumed first and the fats and oils in the food do not go rancid. BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) are the named synthetic ones; sulphur dioxide and sulphite salts are used in wines and dried fruits.
Cleansing agents — soaps and detergents
A soap is a sodium or potassium salt of a long-chain fatty acid. It is made by saponification — boiling a fat or oil with sodium hydroxide, which gives the soap plus glycerol as a by-product.
Sodium salts give hard soaps; potassium salts give softer ones. Adding rosin makes laundry soap, adding a little bithionol makes a medicated soap, and excess free alkali is what makes a poor-quality soap harsh on skin.
Why soap fails in hard water. Hard water contains Ca²⁺ and Mg²⁺ ions. These form calcium and magnesium salts of the fatty acid, which are insoluble and separate as the sticky scum you see on a bathroom bucket. The soap is used up forming scum instead of cleaning.
Detergents solve exactly that problem. A synthetic detergent is a sulphonate or sulphate salt rather than a carboxylate, and its calcium and magnesium salts are water-soluble — so it lathers and cleans even in hard water.
| Type | Structure | Example | Use |
|---|---|---|---|
| Anionic | Long chain with a negatively charged head | Sodium lauryl sulphate; sodium dodecylbenzenesulphonate | Household laundry powders, toothpaste |
| Cationic | Quaternary ammonium salt — positively charged head | Cetyltrimethylammonium bromide | Hair conditioners; also germicidal, but expensive |
| Non-ionic | No ionic head at all | Ester of polyethylene glycol with a long-chain acid | Liquid dishwashing detergents |
Biodegradability is the environmental point. Detergents with heavily branched hydrocarbon chains are broken down slowly by bacteria and build up in rivers, causing foaming. Straight-chain detergents degrade far more easily, which is why manufacturers moved towards them.
How cleansing actually works. Every soap and detergent molecule has two ends: a long hydrocarbon tail that dissolves in grease and a charged or polar head that dissolves in water. In water the molecules gather into a micelle — a spherical cluster with all the tails pointing inwards towards the grease and all the heads facing out into the water. The grease is trapped inside, the outside of the micelle is water-friendly, and rinsing carries the whole assembly away.
Worked example 1 — how much acid does an antacid dose neutralise?
A dose contains 400 mg of magnesium hydroxide. How many moles of hydrochloric acid can it neutralise?
Step 1 — molar mass of Mg(OH)₂ (Mg = 24.305, O = 15.999, H = 1.008):
Mg: 24.305
O: 2 × 15.999 = 31.998
H: 2 × 1.008 = 2.016
M = 24.305 + 31.998 = 56.303; 56.303 + 2.016 = 58.319 g/mol
Step 2 — moles in the dose. 400 mg = 0.400 g:
n = 0.400 ÷ 58.319 = 6.859 × 10⁻³ mol
Check: 58.319 × 0.006859 = 0.4000 g ✓
Step 3 — the balanced equation:
One mole of the hydroxide neutralises two moles of acid, so
n(HCl) = 2 × 6.859 × 10⁻³ = 1.372 × 10⁻² mol, i.e. about 13.7 mmol
Worked example 2 — comparing two antacids per gram
Which neutralises more acid per gram — sodium hydrogencarbonate or magnesium hydroxide?
M(NaHCO₃): Na 22.990 + H 1.008 + C 12.011 + O (3 × 15.999 = 47.997)
22.990 + 1.008 = 23.998; + 12.011 = 36.009; + 47.997 = 84.006 g/mol
NaHCO₃ + HCl → NaCl + H₂O + CO₂ — a 1 : 1 ratio.
Per gram: 1 ÷ 84.006 = 0.01190 mol, so 0.01190 mol of HCl.
Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O — a 1 : 2 ratio.
Per gram: 1 ÷ 58.319 = 0.017147 mol, so 2 × 0.017147 = 0.03429 mol of HCl.
Ratio: 0.03429 ÷ 0.01190 = 2.88
Gram for gram, magnesium hydroxide neutralises roughly 2.9 times as much acid — partly because it is the lighter formula unit, and partly because each unit supplies two hydroxide ions instead of one. This is a mole-ratio result, not a medical recommendation.
Worked example 3 — the pH the antacid is working against
(a) What is the pH of a 0.010 M solution of hydrochloric acid?
HCl is a strong acid and ionises completely, so [H⁺] = 0.010 M = 1.0 × 10⁻² M.
pH = −log₁₀(1.0 × 10⁻²) = −(−2) = 2.00
(b) A stomach fluid sample has pH 1.5. What is its [H⁺]?
[H⁺] = 10⁻¹·⁵ = 10⁰·⁵ × 10⁻² = 3.162 × 10⁻² M ≈ 3.2 × 10⁻² M
Check by going back: −log₁₀(3.162 × 10⁻²) = 2 − log₁₀(3.162) = 2 − 0.500 = 1.50 ✓
Notice how much difference half a pH unit makes: from pH 2.0 to pH 1.5 the hydrogen ion concentration roughly triples, because the pH scale is logarithmic.
Worked example 4 — a small sweetener calculation
Saccharin is about 550 times as sweet as cane sugar. What mass of saccharin gives the sweetness of 5.0 g of sugar?
Mass required = 5.0 ÷ 550 = 0.00909 g = 9.1 mg
Check: 0.00909 × 550 = 5.0 ✓. That tiny mass is the whole point — it delivers sweetness while contributing essentially no food energy.
Mistakes that lose marks
- Mixing up the phenol concentrations. 0.2% is the antiseptic, 1% is the disinfectant. Getting these the wrong way round is a straight lost mark.
- Saying antiseptics and disinfectants differ chemically. They can be the same chemical. What differs is concentration and whether the surface is living.
- Assuming every antibiotic kills bacteria. Bacteriostatic antibiotics only inhibit growth.
- Confusing "broad spectrum" with "bactericidal". Two separate classifications.
- Saying aspartame can be used in baked foods. It is unstable at cooking temperature; sucralose is the one that is stable.
- Explaining detergents as simply "stronger" than soap. The real reason they work in hard water is that their calcium and magnesium salts are soluble, so no scum forms.
- Calling soap a detergent's chemical relative. A soap is a carboxylate salt; a synthetic detergent is a sulphonate or sulphate salt.
- Forgetting the mole ratio in an antacid calculation. Mg(OH)₂ and Al(OH)₃ supply two and three hydroxide ions respectively, not one.
Where this chapter is examined
| Exam | Typical question |
|---|---|
| CBSE Class 12 | Define and distinguish antiseptic and disinfectant with examples; classify a named drug; explain the cleansing action of soap; why soap fails in hard water |
| ISC Class 12 | Saponification, micelle formation, types of detergent, artificial sweeteners with their properties |
| NEET | Direct one-mark matching of drug to class, and sweetener to property |
| Practical / project work | Preparation of soap; comparing the foaming capacity of soap samples in hard and soft water |
Chapter weightages change from time to time, so confirm the current syllabus and question paper design on your board's official website before planning revision time.
Practise the acid–base arithmetic behind the antacid questions. The pH / pOH calculator converts between hydrogen ion concentration, pH, pOH and hydroxide ion concentration, so you can reproduce worked example 3 and try other values until the logarithmic scale feels natural.
Open the pH / pOH Calculator →Finishing the Class 12 syllabus before boards? ABC Chemistry runs Class 11–12 chemistry coaching at its Gurugram centre and online classes across India — details at abcchemistry.in.