Chapter 15 — Chemistry in Everyday Life Exercise Solutions
This chapter is practical and mainly short-answer and table-based. Learn the drug class, one example, and its use/mechanism for each category.
Key Concepts Quick Recap
| Drug Class | Use | Example |
|---|
| Analgesic | Relieves pain (without loss of consciousness) | Aspirin, paracetamol, morphine |
| Antipyretic | Reduces fever | Paracetamol, aspirin |
| Anaesthetic | Causes loss of sensation | Chloroform, ether, lignocaine |
| Antibiotic | Kills/inhibits bacteria | Penicillin, chloramphenicol, tetracycline |
| Antiseptic | Applied to living tissue to kill microbes | Dettol, tincture of iodine, boric acid |
| Disinfectant | Applied to non-living surfaces | Phenol, bleaching powder, chlorine |
| Antacid | Neutralises excess stomach acid | Ranitidine, magnesium hydroxide, Al(OH)₃ |
| Antihistamine | Counteracts histamine response (allergy) | Brompheniramine, terfenadine |
| Antimalarial | Treats malaria | Chloroquine, quinine |
| Tranquiliser | Relieves anxiety/stress | Diazepam (valium), chlordiazepoxide |
Food Additives
| Type | Function | Examples |
|---|
| Antioxidant | Prevents oxidative spoilage | BHT, BHA, vitamin C, vitamin E |
| Artificial sweetener | Sweetens without calories | Aspartame, saccharin, sucralose |
| Preservative | Prevents microbial spoilage | Sodium benzoate, sodium metabisulphite |
| Artificial colour | Adds colour | Tartrazine (yellow), Carmoisine (red) |
| Emulsifier | Stabilises food emulsions | Lecithin, glycerol monostearate |
| Flavour enhancer | Enhances taste/smell | Monosodium glutamate (MSG) |
I. Choose the Best Answer (MCQs)
1. Aspirin is classified as: (a) Antibiotic (b) Analgesic-antipyretic (c) Antiseptic (d) Antacid
Answer(b) Analgesic-antipyretic Aspirin (acetylsalicylic acid) relieves mild-to-moderate pain (analgesic) and reduces fever (antipyretic). It also has anti-inflammatory and anti-clotting properties.
2. Penicillin is: (a) A broad-spectrum antibiotic (b) A narrow-spectrum antibiotic (c) An antifungal (d) An antacid
Answer(b) A narrow-spectrum antibiotic Penicillin acts mainly on Gram-positive bacteria by inhibiting cell-wall synthesis. Broad-spectrum antibiotics (like tetracycline, chloramphenicol) act on both Gram-positive and Gram-negative bacteria.
3. Saccharin is used as an artificial sweetener because: (a) It has high caloric value (b) It is 550 times sweeter than cane sugar with zero calories (c) It contains sucrose (d) It lowers blood pressure
Answer(b) 550 times sweeter with zero calories Saccharin was the first artificial sweetener; used by diabetics. It is excreted unchanged (not metabolised).
4. Which of the following is a biodegradable detergent? (a) Sodium lauryl sulphate (linear chain) (b) Sodium 4-(1,3,5,7-tetramethyloctyl)benzenesulphonate (branched) (c) Alkyl aryl sulphonate (branched) (d) Sulphonated branched-chain hydrocarbons
Answer(a) Sodium lauryl sulphate (linear chain) Biodegradable detergents have linear (unbranched) hydrocarbon chains — bacteria can break these down. Branched-chain detergents are non-biodegradable (resist enzymatic degradation).
5. The use of chloramphenicol is now restricted because: (a) It is expensive (b) It can cause bone marrow damage and aplastic anaemia (c) It is ineffective (d) It has a bad taste
Answer(b) Bone marrow damage Chloramphenicol is a broad-spectrum antibiotic effective against many infections, but it can cause aplastic anaemia (bone marrow stops producing blood cells) — used only when other antibiotics fail.
6. Antacids work by: (a) Absorbing excess acid (b) Neutralising excess hydrochloric acid in the stomach (c) Reducing stomach acid production (d) Killing stomach bacteria
Answer(b) Neutralising HCl Example: Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O. Some antacids (like ranitidine, omeprazole) work by blocking acid secretion — but the mechanism asked here is neutralisation.
7. Which substance, used as an antiseptic, is formed by dissolving iodine in alcohol? (a) Dettol (b) Boric acid (c) Tincture of iodine (d) Hydrogen peroxide
Answer(c) Tincture of iodine Tincture of iodine = 2–3% I₂ in alcohol. Applied to wounds; iodine is released and kills bacteria by oxidising their proteins.
II. Short Answer Questions
Q1. Distinguish between antiseptics and disinfectants with examples.
Answer
| Feature | Antiseptic | Disinfectant |
|---|
| Application | On living tissues (cuts, skin, mucous membranes) | On non-living surfaces (floors, instruments, walls) |
| Concentration | Mild | Stronger (toxic to tissue) |
| Purpose | Prevent infection in wounds | Kill microbes on surfaces |
| Examples | Dettol, tincture of iodine, boric acid, H₂O₂ (3%) | Phenol (1%), bleaching powder, chlorine (for water) |
Note: Phenol is antiseptic at 0.2% concentration, disinfectant at 1% — the same substance, different concentration.
Q2. What are broad-spectrum and narrow-spectrum antibiotics? Give one example each.
Answer
Example: Tetracycline, chloramphenicol, ampicillin.
- Broad-spectrum antibiotics: Effective against both Gram-positive and Gram-negative bacteria. Useful when the type of bacteria is unknown.
Example: Penicillin (mainly Gram-positive); streptomycin (Gram-negative, tuberculosis).
- Narrow-spectrum antibiotics: Effective against only a specific type of bacteria.
Advantage of broad-spectrum: Wider coverage. Disadvantage: Also kills beneficial gut bacteria → superinfection.
Q3. What are food preservatives? Explain with examples.
Answer
Food preservatives are substances added to food to prevent microbial spoilage and extend shelf life.
| Preservative | Use |
|---|
| Sodium benzoate (C₆H₅COONa) | Used in jams, juices, sauces (inhibits yeast/moulds) |
| Sodium metabisulphite (Na₂S₂O₅) | Used in dried fruits, wines (prevents oxidation) |
| Potassium sorbate | Used in cheese, baked goods |
| Salt (NaCl) | Traditional; raises osmotic pressure, dehydrating microbes |
| Sugar | In jams and jellies (high sugar concentration is antimicrobial) |
Natural preservatives: Salt, sugar, vinegar. Chemical preservatives: Sodium benzoate, sulphites.
Q4. Explain the cleansing action of synthetic detergents and why they work in hard water.
Answer
Synthetic detergents are sodium salts of long-chain alkylbenzenesulphonic acids (not fatty acids like soaps).
Cleansing action: Same as soap — hydrophilic sulphonate head points towards water; hydrophobic tail points towards oil → micelle formation → grease removed.
Why in hard water:
- Hard water contains Ca²⁺ and Mg²⁺ ions.
- Soaps react with these ions: 2RCOO⁻Na⁺ + Ca²⁺ → (RCOO)₂Ca↓ (scum — insoluble)
- Synthetic detergents have −SO₃⁻ group: calcium/magnesium sulphonates are soluble → no scum → effective in hard water.
Worked Examples
Example 1 — Drug classes and examples
Pain relief without fever: Analgesic → aspirin, ibuprofen, paracetamol
Fever + pain: Antipyretic analgesic → paracetamol, aspirin
Allergy: Antihistamine → cetirizine, chlorpheniramine
Anxiety/sleep: Tranquiliser → diazepam (valium)
Stomach ulcer: Antacid + H₂-blocker → ranitidine (Zantac)
Bacterial infection: Antibiotic → amoxicillin, ciprofloxacin
Example 2 — Mechanism of antibiotics
Type of action | Mechanism | Example
-----------------------|------------------------------------|------------------
Bactericidal | Kills bacteria directly | Penicillin, streptomycin
Bacteriostatic | Inhibits bacterial growth | Tetracycline, chloramphenicol
Mechanism:
Penicillin → inhibits cell wall synthesis → cell bursts in hypotonic solution
Tetracycline → inhibits protein synthesis (blocks 30S ribosome)
Sulphonamides → compete with PABA (needed for folate synthesis in bacteria)
Example 3 — Artificial sweeteners comparison
Sweetener | Relative sweetness | Caloric value | Notes
-------------|-------------------|---------------|----------------------
Saccharin | 550× | 0 | First artificial sweetener; slightly bitter
Aspartame | 100–200× | Small | Breaks down at high temperature; not for cooking
Sucralose | 600× | 0 | Heat stable; used in cooking
Cyclamate | 30–50× | 0 | Banned in US (suspected carcinogen)
Alitame | 2000× | Very low | Very stable
Example 4 — Dettol as antiseptic
Dettol composition: Chloroxylenol (4.8%) + terpineol + water + soap
Action: Chloroxylenol disrupts bacterial cell membrane
Use: Applied to cuts, wounds; surgical scrub
Concentration: Used diluted (~1% solution) for antiseptic use
Not suitable for: Mucous membranes or eyes (dilute further)
Compare with:
Boric acid: H₃BO₃ — mild antiseptic for eyes (dilute solution)
H₂O₂ (3%): Releases nascent oxygen → kills anaerobes; frothing cleans wounds
Example 5 — Biodegradable vs non-biodegradable detergents
Biodegradable:
Linear alkylbenzenesulphonate (LAS) — linear chains
Bacteria attack the linear chain easily using β-oxidation
Example: Sodium dodecylbenzenesulphonate (linear)
Non-biodegradable:
Branched-chain alkylbenzenesulphonate (ABS) — branched chains
Bacteria cannot attack branched chains efficiently
Causes persistent foam in rivers and water treatment plants
Modern detergents use linear chains to prevent environmental accumulation.
Answer Pattern
1. State the drug class. 2. Write one mechanism (how it works). 3. Give one chemical name example. 4. For comparisons: use table format.
Common Mistakes
- Confusing antiseptic and disinfectant — always check whether it's on living or non-living surfaces.
- Saying all antibiotics are broad-spectrum — penicillin is narrow-spectrum.
- Writing brand names instead of chemical class (say "aspirin/acetylsalicylic acid" not just "Aspirin tablet").
- Mixing analgesic (pain) and antipyretic (fever) — aspirin does both but they are different functions.
- Not mentioning biodegradable = linear chain when comparing detergents.
Exam Checklist
- Drug class and one example are paired correctly.
- Antiseptic vs disinfectant: living tissue vs non-living surface.
- Antacid mechanism is stated (neutralisation of HCl).
- Biodegradable detergent has linear chain (mention this explicitly).
- Food additive category is matched to its example correctly.
