Level 2 — RecallChemistry in Everyday Life (compressed)

Chemistry in Everyday Life (compressed)

⏱ 30 minutes30 marksprintable — key stays hidden on paper

Level: 2 (Recall & Standard Problems) Time Limit: 30 minutes Total Marks: 30

Instructions: Answer all questions. Write chemical equations where required. Use $...$ for any formulae.

Q1. Define the following terms with one example each: (a) Antiseptic (b) Antacid. (2 marks)

Q2. What are broad-spectrum and narrow-spectrum antibiotics? Give one example of each. (3 marks)

Q3. Explain the mechanism by which antacids like $\text{Mg(OH)}_2$ and $\text{NaHCO}_3$ provide relief from acidity. Write the relevant neutralisation reactions. (3 marks)

Q4. (a) What are artificial sweeteners? (b) Name two artificial sweeteners and state one property of each. (3 marks)

Q5. Define food preservatives. Name two common chemical preservatives used in food. (3 marks)

Q6. What are antioxidants in food? Name two examples and state their function. (3 marks)

Q7. Write the chemical reaction for the saponification of a triglyceride (glyceryl tristearate) with sodium hydroxide. Name the products. (4 marks)

Q8. Classify synthetic detergents into three types. Give one example of each and state one use. (3 marks)

Q9. Distinguish between soaps and synthetic detergents on the basis of: (a) behaviour in hard water, (b) biodegradability. (3 marks)

Q10. Why can soaps not be used in acidic medium, whereas detergents can? Explain briefly. (3 marks)

End of Paper

Answer keyMark scheme & solutions

Q1. (2 marks)

(a) Antiseptic: Chemical substance applied to living tissues that kills or prevents growth of microorganisms. Example: Dettol / tincture of iodine / Savlon. (1 mark)
(b) Antacid: Chemical substance that neutralises excess acid (HCl) in the stomach and raises pH to relieve acidity. Example: $\text{Mg(OH)}_2$ / $\text{NaHCO}_3$ / Ranitidine. (1 mark)

Q2. (3 marks)

Broad-spectrum antibiotics: Effective against a wide range of both Gram-positive and Gram-negative bacteria. Example: Chloramphenicol / Tetracycline / Ampicillin. (1.5 marks)
Narrow-spectrum antibiotics: Effective against only one group (either Gram-positive or Gram-negative) of bacteria. Example: Penicillin G. (1.5 marks) Why: Spectrum classification is based on the range of microorganisms an antibiotic acts on.

Q3. (3 marks)

Antacids work by neutralising excess HCl secreted in the stomach, raising the pH and giving relief. (1 mark)
$\text{Mg(OH)}_2 + 2\text{HCl} \rightarrow \text{MgCl}_2 + 2\text{H}_2\text{O}$ (1 mark)
$\text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$ (1 mark) Why: Being basic, they consume acid; they do not stop acid production (that is done by $\text{H}_2$ -blockers like ranitidine).

Q4. (3 marks)

(a) Artificial sweeteners are chemical compounds that give a sweet taste to food but provide little or no calories (energy). (1 mark)
(b) Any two, one property each (2 marks):
- Saccharin: ~550 times sweeter than cane sugar; excreted unchanged, safe for diabetics.
- Aspartame: ~100 times sweeter; unstable at cooking temperature (used in cold foods).
- Sucralose / Alitame: high sweetness, stable to heat.

Q5. (3 marks)

Preservatives: Chemical substances added to food to prevent spoilage due to microbial growth, thus increasing shelf life. (1 mark)
Two examples (any two) (2 marks): Sodium benzoate, sodium metabisulphite/potassium metabisulphite, salt (NaCl), sugar, vegetable oils.

Q6. (3 marks)

Antioxidants: Substances added to food that retard/prevent oxidation (esp. of fats and oils causing rancidity). (1 mark)
Examples (any two) (1 mark): BHT (butylated hydroxytoluene), BHA (butylated hydroxyanisole).
Function: They are more reactive towards oxygen than the food material, so they get oxidised first and protect the food from becoming rancid. (1 mark)

Q7. (4 marks)

Saponification = alkaline hydrolysis of fats/oils (esters) to give soap + glycerol. (1 mark)
Reaction (2 marks):

$\underset{\text{glyceryl tristearate}}{(\text{C}_{17}\text{H}_{35}\text{COO})_3\text{C}_3\text{H}_5} + 3\,\text{NaOH} \rightarrow 3\,\text{C}_{17}\text{H}_{35}\text{COONa} + \underset{\text{glycerol}}{\text{C}_3\text{H}_5(\text{OH})_3}$

Products: Sodium stearate (soap) and glycerol. (1 mark) Why: 3 NaOH per triglyceride because there are three ester linkages.

Q8. (3 marks) (1 mark each type)

Anionic detergents: e.g. Sodium lauryl sulphate / sodium dodecylbenzene sulphonate — used in household laundry & toothpastes.
Cationic detergents: e.g. Cetyltrimethylammonium bromide — used in hair conditioners & germicides.
Non-ionic detergents: e.g. Polyethylene glycol stearate — used in liquid dishwashing detergents.

Q9. (3 marks)

Basis	Soap	Detergent
(a) Hard water	Forms insoluble scum with $\text{Ca}^{2+}/\text{Mg}^{2+}$ , loses cleansing action	Works effectively; Ca/Mg salts are soluble
(b) Biodegradability	Biodegradable (straight chain)	Branched-chain detergents are non-biodegradable, cause pollution

Q10. (3 marks)

Soap is the sodium salt of a weak carboxylic acid. In acidic medium the anion is protonated, forming insoluble free fatty acid, so the soap precipitates and loses cleansing power. (1.5 marks)

$\text{RCOO}^- + \text{H}^+ \rightarrow \text{RCOOH (insoluble)}$

Detergents are salts of strong acids (e.g. sulphonic/sulphuric acids); their anions are not protonated in acid, so they remain effective even in acidic medium. (1.5 marks)

[
  {"claim": "Mg(OH)2 needs 2 mol HCl for neutralisation (stoichiometry)", "code": "HCl_needed = 2; result = (HCl_needed == 2)"},
  {"claim": "Glyceryl tristearate requires 3 NaOH per molecule in saponification", "code": "ester_linkages = 3; NaOH = ester_linkages; result = (NaOH == 3)"},
  {"claim": "Saponification produces 3 soap molecules and 1 glycerol per triglyceride", "code": "soap = 3; glycerol = 1; result = (soap == 3 and glycerol == 1)"},
  {"claim": "NaHCO3 + HCl mole ratio is 1:1", "code": "ratio = Rational(1,1); result = (ratio == 1)"}
]