ChemistryCBSE Class 12 · Chemistry in Everyday Life

Antimicrobials, Antifertility Drugs and Food Chemicals: Class 12 Chemistry

Updated 18 October 2026 · Fact-checked

Antimicrobials destroy or inhibit microbes: antibiotics act inside the body at low concentration, antiseptics are applied to living tissue and disinfectants to non-living objects (0.2 per cent phenol is an antiseptic, 1 per cent a disinfectant). Birth control pills combine synthetic estrogen and progesterone derivatives. Food chemicals include artificial sweeteners, preservatives and antioxidants.

Where a chemical is used decides its type: phenol is an antiseptic at 0.2 per cent but a disinfectant at 1 per cent.

Illustration drawn for QuestionBuddy.

Understand Antimicrobials, Antifertility Drugs and Chemicals in Food

Antimicrobials. An antimicrobial destroys, prevents the development of, or inhibits the pathogenic action of microbes. Antibiotics, antiseptics and disinfectants are antimicrobials.

Antibiotics. Originally, chemicals made by microorganisms that inhibit or destroy other microorganisms; now, a substance made wholly or partly by chemical synthesis that in low concentrations inhibits the growth of or destroys microorganisms by interfering with their metabolism. History: Paul Ehrlich made salvarsan, the first effective treatment for syphilis (Nobel prize 1908); in 1932 prontosil was prepared, which turns into sulphanilamide in the body; in 1929 Alexander Fleming found the antibacterial action of a Penicillium fungus. Bactericidal (kill): penicillin, aminoglycosides, ofloxacin. Bacteriostatic (inhibit): erythromycin, tetracycline, chloramphenicol. Broad spectrum antibiotics act on a wide range of Gram-positive and Gram-negative bacteria (ampicillin, amoxycillin, chloramphenicol, ofloxacin); narrow spectrum act mainly on one group (penicillin G); limited spectrum act on a single organism or disease. Test for penicillin allergy before use.

Antiseptics and disinfectants. Antiseptics are applied to living tissue such as wounds, cuts and ulcers: furacine, soframicine, dettol (chloroxylenol and terpineol), bithionol in soaps, tincture of iodine (2 to 3 per cent iodine in alcohol-water), dilute boric acid for eyes. Disinfectants are applied to non-living objects such as floors, drains and instruments. The same substance can be either, depending on concentration: 0.2 per cent phenol is an antiseptic, 1 per cent phenol a disinfectant. Chlorine at 0.2 to 0.4 ppm in water and sulphur dioxide at very low concentrations are disinfectants.

Antifertility drugs. Birth control pills contain a mixture of synthetic estrogen and progesterone derivatives. Progesterone suppresses ovulation, and its synthetic derivatives are more potent. Norethindrone is the most widely used synthetic progesterone derivative; ethynylestradiol (novestrol) is the estrogen derivative used with it.

Artificial sweeteners. They give sweetness without the calories of sucrose, useful for diabetics and calorie control.

Saccharin (ortho-sulphobenzimide): discovered 1879, about 550 times as sweet as cane sugar, excreted unchanged in urine.
Aspartame: about 100 times as sweet as cane sugar, a methyl ester of a dipeptide of aspartic acid and phenylalanine; unstable at cooking temperature, so used in cold foods and soft drinks.
Alitame: high potency, more stable than aspartame, but sweetness is hard to control.
Sucralose: trichloro derivative of sucrose, looks and tastes like sugar, stable at cooking temperature, no calories.

Preservatives and antioxidants. Preservatives stop spoilage by preventing microbial growth: table salt, sugar, vegetable oils and sodium benzoate (C6H5COONa), used in small amounts and broken down by the body. Antioxidants slow the action of oxygen on food: BHT and BHA (adding BHA to butter increases shelf life from months to years), sometimes with citric acid; sulphur dioxide and sulphites protect wine, beer, sugar syrups and cut or dried fruit and vegetables.

Antimicrobials, Antifertility Drugs and Chemicals in Food: formulas and key facts

Antiseptic vs disinfectant: Antiseptic: living tissue, e.g. 0.2% phenol, dettol, tincture of iodine | Disinfectant: non-living objects, e.g. 1% phenol, chlorine 0.2-0.4 ppm; Same chemical, different concentration.
Antibiotic effect: $B a c t er i c i d a l : p e ni c i l l in, o f l o x a c in, amin o g l y cos i d es ∣ B a c t er i os t a t i c : er y t h r o m y c in, t e t r a cy c l in e, c h l or am p h e ni co l$; Kill versus inhibit.
Sweeteners: Saccharin 550 times sugar
Aspartame 100 times sugar, unstable on cooking
Sucralose stable on cooking; Alitame: stable but sweetness hard to control.

Saccharin	550 times sugar
Aspartame	100 times sugar, unstable on cooking
Sucralose	stable on cooking

How to solve Antimicrobials, Antifertility Drugs and Chemicals in Food questions

Formative (school) assessment only in 2026-27. Expect classification, concentration-based reasoning and simple ratio arithmetic.

1Decide where the chemical is used: body tissue (antiseptic) or object (disinfectant), or inside the body (antibiotic).
2Use the concentration clue: 0.2 per cent phenol versus 1 per cent phenol.
3For dilution, apply C1 x V1 = C2 x V2.
4For sweetness, divide the sugar mass by the sweetness factor.
5For ppm, 1 ppm = 1 g in 10^6 g of solution.

Antimicrobials, Antifertility Drugs and Chemicals in Food in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Diluting a disinfectant

Suppose a cleaner has 10 per cent phenol stock and needs 500 mL of 1 per cent solution to wash drains (invented task).

How much stock and how much water are needed?

Try it first, then show the solutionSolution

C1V1 = C2V2: 10 x V1 = 1 x 500.
V1 = 50 mL.
Water = 500 - 50 = 450 mL.

Answer: V1 = (1 x 500) / 10 = 50 mL of stock plus 450 mL of water gives 500 mL of 1 per cent phenol, a disinfectant.

Memory hook: 1 per cent for floors, 0.2 per cent for skin.

Sweetener for a cold drink

Suppose a drink needs the sweetness of 11 g of cane sugar (invented) but the maker wants a zero-calorie sweetener.

How much saccharin (550 times as sweet) and how much aspartame (100 times) would give the same sweetness, and which suits a cold drink?

Try it first, then show the solutionSolution

Saccharin = 11 / 550 = 0.02 g.
Aspartame = 11 / 100 = 0.11 g.
Aspartame is unstable at cooking temperature, so suits cold drinks.

Answer: Saccharin 11 / 550 = 0.02 g; aspartame 11 / 100 = 0.11 g. Aspartame is unstable at cooking temperature, so it is suitable only for cold foods and soft drinks like this one.

Memory hook: Divide sugar mass by the sweetness factor.

Tricks to remember Antimicrobials, Antifertility Drugs and Chemicals in Food

Short memory aids. Say each one aloud once, then use it on a question the same day.

Cide kills, static stops
Bactericidal kills; bacteriostatic inhibits.
Use it when: Antibiotics.
Septic = skin, Dis = door
Antiseptic on skin; disinfectant on floors and doors.
Use it when: Distinction.
Aspartame is cold-only
Unstable when cooked.
Use it when: Sweeteners.

Antimicrobials, Antifertility Drugs and Chemicals in Food: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Phenol use · 1 mark · MCQBoard level

A 1 per cent solution of phenol is used as:
(a) an antiseptic
(b) a disinfectant
(c) an antibiotic
(d) an analgesic

Try it first, then show the solutionSolution

0.2 per cent phenol is an antiseptic; 1 per cent phenol is a disinfectant (1 mark).

Answer: (b) a disinfectant

Example 2: Antiseptic vs disinfectant (2 marks) · 2 marks · Very short answerBoard level

Distinguish an antiseptic from a disinfectant with one example each. (2 marks)

Try it first, then show the solutionSolution

Antiseptic: applied to living tissue, e.g. dettol or tincture of iodine (1 mark).
Disinfectant: applied to non-living objects, e.g. 1 per cent phenol or chlorine (1 mark).

Answer: Antiseptics are applied to living tissue such as wounds, for example dettol. Disinfectants are applied to non-living objects such as floors, for example 1 per cent phenol.

Example 3: Dilution and ppm (4 marks) · 4 marks · Short answerHarder board level

(a) How much 10 per cent phenol stock is needed to make 2.0 L of 0.2 per cent antiseptic solution? (b) How many grams of chlorine are needed to disinfect 5000 L of water at 0.4 ppm (take 1 L water = 1000 g)? (4 marks)

Try it first, then show the solutionSolution

(a) 10 x V1 = 0.2 x 2.0 L, so V1 = 0.04 L = 40 mL (1 mark); water = 1960 mL (1 mark).
(b) Mass of water = 5000 x 1000 = 5 x 10^6 g (1 mark).
0.4 ppm = 0.4 g per 10^6 g, so chlorine = 0.4 x 5 = 2 g (1 mark).

Answer: (a) V1 = (0.2 x 2.0) / 10 = 0.04 L = 40 mL of stock, mixed with 1960 mL of water. (b) 5000 L is 5 x 10^6 g of water; at 0.4 ppm, chlorine needed = 0.4 x 5 = 2 g.

Example 4: Antibiotic spectrum (5 marks) · 5 marks · Long answerHarder board level

Explain broad, narrow and limited spectrum antibiotics with examples, and the difference between bactericidal and bacteriostatic drugs. (5 marks)

Try it first, then show the solutionSolution

Broad spectrum: wide range of Gram-positive and Gram-negative bacteria; ampicillin, amoxycillin, ofloxacin (1 mark).
Narrow spectrum: mainly one group; penicillin G (1 mark).
Limited spectrum: a single organism or disease (1 mark).
Bactericidal kills bacteria: penicillin, ofloxacin (1 mark).
Bacteriostatic inhibits growth: erythromycin, tetracycline (1 mark).

Answer: Broad spectrum antibiotics, such as ampicillin, amoxycillin and ofloxacin, act on a wide range of Gram-positive and Gram-negative bacteria. Narrow spectrum antibiotics, such as penicillin G, act mainly on one group, and limited spectrum antibiotics act on a single organism or disease. Bactericidal drugs such as penicillin kill bacteria, while bacteriostatic drugs such as erythromycin and tetracycline inhibit their growth.

Example 5: Choosing a sweetener · 4 marks · Case-basedHOTS / competency

A bakery wants a calorie-free sweetener for cakes baked at high temperature. (i) Why is aspartame unsuitable? (1) (ii) Which sweetener from the chapter is suitable and why? (2) (iii) Name one preservative for the packaged cake. (1)

Try it first, then show the solutionSolution

(i) Aspartame is unstable at cooking temperature (1 mark).
(ii) Sucralose: stable at cooking temperature, looks and tastes like sugar and gives no calories (2 marks).
(iii) Sodium benzoate (1 mark).

Answer: (i) Aspartame is unstable at cooking temperature. (ii) Sucralose is stable at cooking temperature, tastes like sugar and gives no calories. (iii) Sodium benzoate.

Where students lose marks in Antimicrobials, Antifertility Drugs and Chemicals in Food

The slips examiners see most often, and what to write instead.

Mistake: Mixing up antiseptic and disinfectant by name
Same chemical used for both.
Wrong working
Phenol is only a disinfectant.
Right working
0.2 per cent phenol is an antiseptic; 1 per cent phenol is a disinfectant.
Do this: Always quote the concentration.
Usually costs: 1 mark.
Mistake: Dilution volumes swapped
Mixing C1 and C2.
Wrong working
V1 = (10 x 500) / 1 = 5000 mL.
Right working
V1 = (C2 x V2) / C1 = (1 x 500) / 10 = 50 mL.
Do this: Stock is the more concentrated one.
Usually costs: 2 marks.
Mistake: Aspartame for baking
Forgetting stability.
Wrong working
Use aspartame in cakes.
Right working
Aspartame is unstable at cooking temperature; sucralose is stable.
Do this: Cold only for aspartame.
Usually costs: 1 mark.

Exam tips

Chemistry in Everyday Life is formative (school) assessment only in 2026-27.
Quote the concentration with every antiseptic or disinfectant.
Keep sweetness factors handy: 550 and 100.

Practice questions on Antimicrobials, Antifertility Drugs and Chemicals in Food

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
BHA is used in food as:
(a) a sweetener
(b) an antioxidant
(c) an antibiotic
(d) a tranquiliser
Hint
Butter shelf life.
Answer
(b) an antioxidant
Q2 · 2 marks · Very short answerBoard level
What are birth control pills made of? (2 marks)
Hint
Two hormone derivatives.
Answer
A mixture of synthetic estrogen and progesterone derivatives; the progesterone derivative suppresses ovulation.
Q3 · 3 marks · Short answerHarder board level
How much saccharin (550 times as sweet as sugar) matches 27.5 g of cane sugar, and how much aspartame (100 times)? (3 marks)
Hint
Divide by the factor.
Answer
Saccharin = 27.5 / 550 = 0.05 g. Aspartame = 27.5 / 100 = 0.275 g.
Q4 · 5 marks · Long answerHarder board level
A lab technician has 20 per cent phenol stock and wants 400 mL of 1 per cent disinfectant. Find the stock and water volumes, and explain why the same chemical at 0.2 per cent would be used differently. (5 marks)
Hint
C1V1 = C2V2.
Answer
20 x V1 = 1 x 400, so V1 = 20 mL of stock plus 380 mL of water. At 0.2 per cent phenol is mild enough to be an antiseptic on living tissue, while 1 per cent is a disinfectant for non-living objects like floors and drains.
Q5 · 1 mark · Assertion-reasonHOTS / competency
Assertion (A): Sucralose can be used in baking.
Reason (R): Sucralose is stable at cooking temperature.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Hint
Stability on cooking.
Answer
(a) Both A and R are true, and R is the correct explanation of A.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Who made salvarsan?Show answer
Paul Ehrlich.
2.What is dettol made of?Show answer
Chloroxylenol and terpineol.
3.Name a progesterone derivative used in pills.Show answer
Norethindrone.
4.Which sweetener is a trichloro derivative of sucrose?Show answer
Sucralose.

Antimicrobials, Antifertility Drugs and Chemicals in Food: frequently asked questions

What is the difference between an antibiotic and an antiseptic?

Antibiotics act on microbes in the body at low concentration; antiseptics are applied to living tissue such as cuts.

What is an antioxidant in food?

A chemical like BHA or BHT that slows the action of oxygen on food.

Why is sodium benzoate used?

It prevents microbial growth and is broken down by the body.