Chemistry in Everyday Life Class 12: Medicines and Food Chemicals (School-Assessed)

What Chemistry in Everyday Life is about

In real board papers: asked in 1 of the 8 board papers we hold (2023 to 2026), on average 0.1 marks per paper. See the questions

Key concepts

Drugs and drug–target interaction

NCERT section CBSE reading material: 16.1 Drugs; 16.2 Drug–Target Interaction

Drugs are chemicals of low molecular mass (about 100–500 u) that interact with large molecules (macromolecular targets) in the body and produce a biological response. When the response is therapeutic and useful, they are called medicines, used to diagnose, prevent and treat diseases. Most drugs are potential poisons at doses higher than recommended. Using chemicals for a therapeutic effect is chemotherapy.

Biological targets include enzymes (proteins that catalyse reactions), receptors (proteins in the body's communication system), carrier proteins, nucleic acids, lipids and carbohydrates.

Enzymes as targets: an enzyme (i) holds the substrate in its active site through ionic bonds, hydrogen bonds, van der Waals or dipole–dipole interactions, and (ii) provides functional groups that attack the substrate. Drugs that block these actions are enzyme inhibitors:

• Competitive inhibitors compete with the natural substrate for the active site.
• Some drugs bind to a different site, the allosteric site, changing the shape of the active site so the substrate cannot recognise it.
• If the enzyme–inhibitor bond is a strong covalent bond, the enzyme is blocked permanently; the body breaks down the complex and makes new enzyme.

Antacids and antihistamines

NCERT section CBSE reading material: 16.3.1 Antacids; 16.3.2 Antihistamines

Antacids: too much stomach acid causes irritation and pain, and in severe cases ulcers.

• Early treatment used sodium hydrogencarbonate or a mixture of aluminium and magnesium hydroxides. Excess hydrogencarbonate can make the stomach alkaline and trigger even more acid; insoluble metal hydroxides are better because they do not raise the pH above neutral. These treat only the symptoms, not the cause.
• A breakthrough came when it was found that histamine stimulates secretion of pepsin and HCl in the stomach. Cimetidine (Tagamet) was designed to stop histamine from interacting with receptors in the stomach wall, so less acid is released. It was the world's largest selling drug until ranitidine (Zantac) was discovered.

Antihistamines: histamine is a potent vasodilator. It contracts smooth muscles in the bronchi and gut, relaxes muscles in the walls of fine blood vessels, and causes the nasal congestion of a cold and the allergic response to pollen. Brompheniramine (Dimetapp) and terfenadine (Seldane) compete with histamine for its receptor binding sites.

Why don't antihistamines reduce stomach acid? Because anti-allergic and antacid drugs act on different receptors.

Neurologically active drugs: tranquilisers and analgesics

NCERT section CBSE reading material: 16.3.3 Neurologically Active Drugs

These drugs affect the transfer of messages from nerves to receptors.

Tranquilisers treat stress and mild or severe mental illness by relieving anxiety, stress, irritability or excitement; they are part of sleeping pills.

• Antidepressants: low levels of the neurotransmitter noradrenaline lower signalling activity and cause depression. Drugs such as iproniazid and phenelzine inhibit the enzymes that break down noradrenaline, so it acts on its receptor for longer.
• Chlordiazepoxide and meprobamate are mild tranquilisers for relieving tension; equanil is used to control depression and hypertension.
• Barbiturates (derivatives of barbituric acid: veronal, amytal, nembutal, luminal, seconal) are hypnotic (sleep-producing). Valium and serotonin are also used as tranquilisers.

Analgesics reduce or abolish pain without impairing consciousness or causing confusion or paralysis.

• Non-narcotic (non-addictive): aspirin and paracetamol. Aspirin inhibits the synthesis of prostaglandins, which cause inflammation and pain. Such drugs relieve skeletal pain (arthritis), reduce fever (antipyretic) and prevent platelet coagulation; aspirin's anti-clotting action is used to help prevent heart attacks.
• Narcotic: morphine and its homologues (opiates, from the opium poppy). In medicinal doses they relieve pain and produce sleep; in poisonous doses they cause stupor, coma, convulsions and death. They are used for postoperative pain, cardiac pain, the pain of terminal cancer and in childbirth.

Antimicrobials: antibiotics, antiseptics and disinfectants

NCERT section CBSE reading material: 16.3.4 Antimicrobials

An antimicrobial destroys, prevents the development of, or inhibits the pathogenic action of microbes: antibacterial, antifungal, antiviral or antiparasitic drugs. 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 (arsphenamine), the first effective treatment for syphilis (Nobel prize 1908). He noticed that its –As=As– link resembles the –N=N– of azo dyes. In 1932 prontosil was prepared; in the body it turns into sulphanilamide, the real active compound, which led to the sulpha drugs (sulphapyridine). In 1929 Alexander Fleming found the antibacterial action of a *Penicillium* fungus.
• Bactericidal (kill): penicillin, aminoglycosides, ofloxacin. Bacteriostatic (inhibit): erythromycin, tetracycline, chloramphenicol.
• Spectrum of action: broad spectrum antibiotics act on a wide range of Gram-positive and Gram-negative bacteria (ampicillin, amoxycillin, chloramphenicol, vancomycin, ofloxacin); narrow spectrum act mainly on one group (penicillin G); limited spectrum act on a single organism or disease. Patients must be tested for penicillin allergy before it is given. Chloramphenicol is absorbed rapidly from the gut and given orally for typhoid, dysentery, acute fever, some urinary infections, meningitis and pneumonia.

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

Antifertility drugs

NCERT section CBSE reading material: 16.3.5 Antifertility Drugs

Antibiotics nearly doubled life expectancy, and population growth brought problems of food, environment and jobs, leading to family planning. Birth control pills contain a mixture of synthetic estrogen and progesterone derivatives, both hormones. Progesterone suppresses ovulation, and synthetic progesterone derivatives are more potent than progesterone itself.

• Norethindrone: the most widely used synthetic progesterone derivative.
• Ethynylestradiol (novestrol): the estrogen derivative used with it.

Chemicals in food: sweeteners, preservatives and antioxidants

NCERT section CBSE reading material: 16.3.6 Artificial Sweetening Agents; 16.3.7 Food Preservatives; 16.3.8 Antioxidants in Food

Artificial sweetening agents give sweetness without the calories of sucrose, useful for diabetic people and those controlling calorie intake.

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

Food preservatives stop spoilage by preventing microbial growth: table salt, sugar, vegetable oils and sodium benzoate (C₆H₅COONa), which is added only in small amounts and is broken down by the body. Sorbate and propanoate salts serve the same purpose.

Antioxidants slow the action of oxygen on food. The commonest are butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA); adding BHA to butter increases its shelf life from months to years. BHT and BHA are sometimes used with citric acid for more effect. Sulphur dioxide and sulphites protect drinks such as wine and beer, sugar syrups, and fruit and vegetables that have been cut, peeled or dried.

Chemistry in real life: Chemistry in Everyday 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.

Topics in this chapter

• Antimicrobials, Antifertility Drugs and Chemicals in Food
• Drug-Target Interaction, Antacids, Antihistamines, Tranquilisers and Analgesics

Chemistry in Everyday Life formula sheet

Drug size

$M\approx 100-500\text{u}$

Low molecular mass chemicals acting on macromolecular targets.

Antiseptic vs disinfectant (phenol)

$0.2\%\text{phenol: antiseptic};1\%\text{phenol: disinfectant}$

The same chemical, different concentrations.

Sweetness compared with cane sugar

$\text{saccharin}\approx 550\times ;\text{aspartame}\approx 100\times$

Aspartame is unstable at cooking temperature; sucralose is stable.

Dettol

$\text{chloroxylenol}+\text{terpineol}$

A common antiseptic mixture.

Tincture of iodine

$2-3\%\text{iodine in alcohol-water}$

Applied on wounds.

Chlorine as disinfectant

$0.2-0.4\text{ppm}C{l}_2\text{in water}$

Used for drinking water.

Tricks to remember Chemistry in Everyday Life

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

• Antiseptic = Alive, Disinfectant = Dead objects

  Antiseptics go on Alive tissue; Disinfectants go on Dead (non-living) things.

  Use it when: Distinguishing the two.

• Cidal Cuts, Static Stops

  Bactericidal antibiotics kill (penicillin, aminoglycosides, ofloxacin); bacteriostatic ones stop growth (erythromycin, tetracycline, chloramphenicol).

  Use it when: Classifying antibiotics.

• Saccharin 550, Aspartame 100

  Saccharin is the 'super' sweetener (about 550 times sugar); aspartame is 'only' about 100 times but more popular.

  Use it when: Sweetness questions.

• BHA keeps Butter Happy for Ages

  BHA in butter raises shelf life from months to years.

  Use it when: Antioxidant examples.

Chemistry in Everyday Life: previous year questions

• Asked in 1 of the 8 board papers we hold (2023 to 2026), on average 0.1 marks per paper; 1 questions in all, counting OR alternatives. In 2 of 4 sample papers.

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Solved board questions from Chemistry in Everyday Life

Real questions from recent papers. Try each one first, then open our step-by-step solution with marks per step.

Every Chemistry in Everyday Life question, by year

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. 1.What is chemotherapy?Show answer

   The use of chemicals for therapeutic effect.

2. 2.What is a competitive inhibitor?Show answer

   A drug that competes with the natural substrate for the active site of an enzyme.

3. 3.Why is cimetidine better than a simple antacid?Show answer

   It blocks histamine from acting on stomach-wall receptors, so less acid is released, treating the cause rather than just the symptom.

4. 4.Why do antihistamines not affect stomach acid?Show answer

   Anti-allergic and antacid drugs act on different receptors.

5. 5.Name two non-narcotic analgesics.Show answer

   Aspirin and paracetamol.

6. 6.Which drug did Paul Ehrlich develop for syphilis?Show answer

   Salvarsan (arsphenamine).

7. 7.Give one broad spectrum and one narrow spectrum antibiotic.Show answer

   Broad: chloramphenicol (or ampicillin, amoxycillin, ofloxacin, vancomycin); narrow: penicillin G.

8. 8.What does dettol contain?Show answer

   Chloroxylenol and terpineol.

9. 9.Name the synthetic hormones in birth control pills.Show answer

   Norethindrone (progesterone derivative) and ethynylestradiol (novestrol, an estrogen derivative).

10. 10.Name a food preservative and an antioxidant.Show answer

    Sodium benzoate; BHA or BHT.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you explain competitive and allosteric inhibition of enzymes?
• ☐Can you explain why insoluble metal hydroxides are better antacids than sodium hydrogencarbonate?
• ☐Can you explain how cimetidine and ranitidine reduce acidity?
• ☐Can you distinguish narcotic and non-narcotic analgesics with examples?
• ☐Can you classify antibiotics as bactericidal or bacteriostatic and by spectrum?
• ☐Can you give three examples each of antiseptics and disinfectants?
• ☐Can you compare saccharin, aspartame, alitame and sucralose?
• ☐Can you name two preservatives and two antioxidants with their uses?

Chemistry in Everyday Life: frequently asked questions