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📗 Nayab Subba syllabus: Paper I, General Knowledge, Unit 1.8.4 · Open the full Nayab Subba course
Unit 1.8.4 of the Nayab Subba syllabus asks about materials we use every day: soap, plastics, fibre, glass, fertilisers and pesticides. Questions usually test what they are made of, their types and their effects.
1. Soap and detergent
- Soap is made by heating fats or oils with an alkali. This reaction is called saponification; glycerol (glycerine) is a by-product.
- Sodium hydroxide (caustic soda, NaOH) gives hard soap (bathing and washing bars); potassium hydroxide (KOH) gives soft soap (liquid soap, shaving soap).
- A soap molecule has a water-loving (hydrophilic) head and an oil-loving (hydrophobic) tail. The tails hold the dirt and oil, forming micelles that are washed away by water.
- In hard water (with calcium and magnesium salts) soap forms scum and does not lather well.
- Detergents are synthetic cleaning agents (sodium salts of sulphonic acids). They work well even in hard water, but some are non-biodegradable and cause foam and water pollution; phosphates in detergents cause eutrophication (excess algae) in lakes.
2. Plastics
- Plastics are polymers: long chains made by joining many small units (monomers).
| Type | Feature | Examples |
|---|---|---|
| Thermoplastic | Softens on heating; can be re-shaped and recycled | Polythene, PVC, polystyrene, nylon, PET bottles |
| Thermosetting | Sets hard once; does not soften on heating | Bakelite (switches, handles), melamine (crockery) |
- Polythene (polyethylene) is used for bags; PVC for pipes and cables; Teflon for non-stick pans; bakelite was the first fully synthetic plastic.
- Problems: plastics are non-biodegradable, block drains, harm animals, and burning them releases toxic gases (dioxins). Microplastics now pollute rivers and food.
- Solutions: reduce, reuse, recycle (3R), ban thin plastic bags, use cloth and paper bags.
3. Fibres
| Type | Source | Examples |
|---|---|---|
| Natural – plant | Plant cells (cellulose) | Cotton, jute, hemp, allo (Himalayan nettle), flax |
| Natural – animal | Protein | Wool (sheep, yak), silk (silkworm cocoon), pashmina (mountain goat) |
| Semi-synthetic | Made from natural cellulose | Rayon (artificial silk) |
| Synthetic | Petrochemicals | Nylon (first fully synthetic fibre, 1935), polyester (terylene), acrylic |
- Synthetic fibres are strong, light and quick-drying but melt and stick to the skin in fire and are not biodegradable.
- Nepal is famous for pashmina, allo and handmade dhaka cloth.
4. Glass
- Glass is made by melting silica (sand) with soda ash (sodium carbonate) and limestone (calcium carbonate) at a very high temperature and cooling it quickly. It is an amorphous solid (a “super-cooled liquid”).
| Type | Special feature / use |
|---|---|
| Soda-lime glass | Common window glass and bottles |
| Borosilicate (Pyrex) glass | Resists heat; laboratory and cookware |
| Lead (crystal) glass | Sparkles; decorative items, lenses |
| Toughened/safety glass | Vehicle windows |
| Coloured glass | Metal oxides: cobalt oxide → blue, chromium oxide → green |
- Glass is recyclable and does not rust or react with most chemicals.
5. Fertilisers
- Plants need mainly nitrogen (N), phosphorus (P) and potassium (K) (NPK).
| Fertiliser | Main nutrient |
|---|---|
| Urea | Nitrogen (about 46% N) |
| DAP (diammonium phosphate) | Phosphorus and nitrogen |
| Potash (MOP) | Potassium |
- Organic manure and compost improve soil structure; bio-fertilisers (for example *Rhizobium* bacteria, blue-green algae) fix nitrogen naturally.
- Overuse of chemical fertiliser makes soil acidic, pollutes water and causes eutrophication. Nepal imports chemical fertiliser, and shortages during the planting season are a common problem.
6. Pesticides
- Pesticides kill or control harmful organisms.
| Type | Controls |
|---|---|
| Insecticide | Insects (aphids, mosquitoes) |
| Herbicide (weedicide) | Weeds |
| Fungicide | Fungi (blight) |
| Rodenticide | Rats and mice |
- DDT is a well-known insecticide that is now banned/restricted because it stays in the environment and builds up in food chains (biomagnification).
- Pesticide residue on vegetables can harm health; Nepal checks residues at markets (for example, rapid bioassay tests).
- Safer methods: Integrated Pest Management (IPM), bio-pesticides (neem), correct dosage and waiting period before harvest.
📌 Key points to remember
- Soap = fat/oil + alkali (saponification); NaOH → hard soap, KOH → soft soap; detergents work in hard water.
- Thermoplastics soften on heating (polythene, PVC); thermosetting plastics do not (bakelite, melamine).
- Natural fibres: cotton, jute, allo, wool, silk; rayon is semi-synthetic; nylon is the first synthetic fibre.
- Glass = silica + soda ash + limestone; borosilicate (Pyrex) resists heat; cobalt gives blue colour.
- NPK fertilisers: urea (N, about 46%), DAP (P), potash (K); overuse harms soil and water.
- Pesticides: insecticide, herbicide, fungicide, rodenticide; DDT is banned due to biomagnification; IPM is safer.
📝 Quiz
Test yourself: Materials in Daily Life
52 questions check what you read about Soap and detergent, Glass and Pesticides. Each attempt picks 25 at random.
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