CBSE Important Questions Class 12 Chemistry Chapter 12 – Chemistry in Everyday Life

Class 12 Chemistry Chapter 12 Chemistry in Everyday Life is part of the CBSE Class 12 Chemistry syllabus. It shows how chemistry is used in medicine, food and cleaning products. Students learn how drugs act on the body, the different classes of medicines such as antacids, antihistamines, tranquillisers, analgesics, antibiotics and antiseptics, the chemicals added to food, and the chemistry of soaps and detergents.

These CBSE important questions for Class 12 Chemistry Chapter 12 cover the meaning of a drug-target interaction, the difference between an antiseptic and a disinfectant, antacids and antihistamines, broad and narrow spectrum antibiotics, artificial sweeteners, food preservatives, and why detergents work in hard water while soaps do not. Every question has a clear step-by-step solution in simple English, so students can practise on their own, parents can check the working, and teachers can use them for class tests.

Q1. What are drugs? What is meant by chemotherapy?

Answer: Drugs are chemicals of low molecular mass (about 100 to 500 u) that interact with the body's own molecules and produce a biological response. When that response is helpful and the drug is used to treat disease, it is called a medicine.
Chemotherapy is the use of chemicals (drugs) for treating diseases. The term covers the use of medicines to kill or stop the growth of disease-causing micro-organisms and cancer cells.
It is important to note that drugs can be poisonous in higher doses, which is why they must always be taken in the prescribed amount.

Q2. What is the difference between an antiseptic and a disinfectant? Give one example of each.

Answer: Both kill micro-organisms, but they differ in where they are used and in what strength.
• Antiseptics are applied to living tissue — on wounds, cuts and skin. They do not harm the body at the concentrations used.
Examples: dettol, savlon, tincture of iodine, 0.2% phenol solution.
• Disinfectants are applied to non-living objects such as floors, drains and instruments. They are too strong to be used on skin.
Examples: 1% phenol solution, chlorine in drinking water, sulphur dioxide.
Interestingly, phenol is both: at 0.2% it is an antiseptic, and at 1% it becomes a disinfectant. So the difference is often simply one of concentration.

Q3. What are antacids? Name two antacids and explain how they work.

Answer: Antacids are medicines that reduce the excess acid in the stomach and so relieve acidity, heartburn and indigestion.
Two antacids: sodium hydrogen carbonate (baking soda) and magnesium hydroxide (milk of magnesia). Aluminium hydroxide is another.
How they work: These are weak bases that neutralise the excess hydrochloric acid in the stomach.
NaHCO₃ + HCl → NaCl + H₂O + CO₂
A better modern approach: Drugs such as ranitidine and cimetidine do not just neutralise the acid — they stop the stomach from producing so much acid in the first place, by blocking the histamine receptors that trigger acid release. This treats the cause rather than the symptom.

Q4. What are antihistamines? Give two examples and state their use.

Answer: Antihistamines are drugs that block the natural action of histamine in the body. Histamine is released during an allergic reaction and causes inflammation, swelling, a runny nose and skin rashes.
Two examples: brompheniramine (Dimetapp) and terfenadine (Seldane). Diphenhydramine is another well-known one.
Use: They are used to treat allergies, hay fever, skin rashes, insect bites and the symptoms of the common cold.
Interesting point: Antihistamines do not affect the secretion of stomach acid, even though histamine also triggers that. This is because the two kinds of histamine receptors are different, and these drugs fit only the allergy receptor.

Q5. What are tranquillisers? Give two examples.

Answer: Tranquillisers are chemicals that act on the central nervous system to relieve anxiety, stress, irritability and mental excitement. They form an important part of the treatment for mental illness, and are a major component of sleeping pills.
Two examples: equanil (used for depression and high blood pressure) and veronal. Others are chlordiazepoxide, meprobamate and valium.
How they work: Some, such as the barbiturates, act as hypnotics and induce sleep. Others, such as iproniazid, stop the breakdown of noradrenaline in the brain, which lifts the mood.
These drugs must be taken only on a doctor's advice, since they can be habit-forming.

Q6. What is the difference between broad spectrum and narrow spectrum antibiotics? Give one example of each.

Answer: • Broad spectrum antibiotics kill or stop a wide range of different bacteria, both Gram-positive and Gram-negative.
Examples: chloramphenicol, ampicillin, tetracycline.
• Narrow spectrum antibiotics are effective against only one group of organisms, usually either Gram-positive or Gram-negative.
Examples: penicillin G.
There is also a third class, limited spectrum antibiotics, which work against a single organism or a single disease.
Also worth knowing: antibiotics are called bactericidal if they kill the bacteria (such as penicillin) and bacteriostatic if they only stop them multiplying (such as tetracycline).

Q7. What are artificial sweeteners? Name two and state one advantage of each.

Answer: Artificial sweeteners are chemicals that taste sweet but supply little or no calories. They let people enjoy a sweet taste without the sugar, which matters for diabetics and for those controlling their weight.
Two examples:
1. Saccharin: about 550 times sweeter than cane sugar. It is completely inert and passes out of the body unchanged, so it is entirely safe for diabetics.
2. Aspartame: about 100 times sweeter than sugar, and the most successful of the modern sweeteners. Its limitation is that it breaks down when heated, so it can only be used in cold foods and soft drinks, not in cooking.
Others are sucralose, which is stable at cooking temperature, and alitame, which is very hard to control the sweetness of.

Q8. What are food preservatives? Give two examples.

Answer: Food preservatives are substances added to food to prevent it from spoiling due to the growth of micro-organisms. They stop fermentation, souring and decomposition.
Two examples:
1. Sodium benzoate (C₆H₅COONa), which is the most commonly used chemical preservative. It is converted in the body to hippuric acid and excreted, so it is safe in small amounts.
2. Salts of sorbic acid and propanoic acid, widely used in bread and cheese.
Common preservatives at home: table salt and sugar are the oldest preservatives of all, used in pickles, jams and squashes. Vegetable oils are also used in pickles for the same purpose.

Q9. What are soaps and detergents? Why do detergents work in hard water while soaps do not?

Answer: Soaps are the sodium or potassium salts of long chain fatty acids, such as sodium stearate. They are made by heating fat or oil with sodium hydroxide, a process called saponification.
Detergents are sodium salts of long chain benzene sulphonic acids or of long chain alkyl hydrogen sulphates.
Why soaps fail in hard water: Hard water contains calcium and magnesium ions. These react with soap to form insoluble calcium and magnesium stearates, which appear as a sticky white scum. The soap is wasted and no lather forms.
2C₁₇H₃₅COONa + Ca²⁺ → (C₁₇H₃₅COO)₂Ca↓ + 2Na⁺
Why detergents work: The calcium and magnesium salts of sulphonic acids are soluble in water. So no scum forms and the detergent keeps on cleaning even in hard water.

Q10. How do drugs act as enzyme inhibitors?

Answer: Many drugs work by blocking an enzyme that a disease-causing organism needs. There are two ways this happens.
1. Competitive inhibition: The drug has a shape very similar to the enzyme's natural substrate, so it fits into the active site and sits there. The real substrate cannot get in, and the enzyme cannot do its job.
2. Allosteric inhibition: The drug binds to a different site on the enzyme, called the allosteric site. This changes the shape of the active site so that the substrate no longer fits.
If the drug binds through strong covalent bonds, the inhibition is permanent and the body has to make fresh enzyme. Most drugs bind weakly, so the effect wears off.

Q11. What are analgesics? How are they classified?

Answer: Analgesics are drugs that reduce or remove pain without causing loss of consciousness, mental confusion or paralysis.
They are classified into two groups.
1. Non-narcotic (non-addictive) analgesics: Example: aspirin and paracetamol. Aspirin also brings down fever and thins the blood, so small doses are given to prevent heart attacks.
2. Narcotic analgesics (opiates): Examples: morphine, codeine and heroin. These bring relief from severe pain and produce sleep, and are used after surgery and in terminal cancer.
Warning: Narcotic analgesics are habit-forming and are dangerous in larger doses, causing stupor, coma and even death. They are given only under strict medical supervision.

Q12. What are antifertility drugs and what do they contain?

Answer: Antifertility drugs are chemicals used to control the birth rate by preventing pregnancy. They are the active ingredients of oral contraceptive pills.
What they contain: They are a mixture of synthetic oestrogen and progesterone derivatives. These are the two natural female sex hormones that control the menstrual cycle and ovulation.
Two examples: norethindrone, a synthetic progesterone derivative, and ethynylestradiol (novestrol), a synthetic oestrogen derivative.
How they work: Progesterone suppresses ovulation. The synthetic versions are more potent than the natural hormones and can be taken by mouth, so a combination of the two is used in the pill.

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