Fertilizers and Paints
~7 min read
- Fertilizers: Substances added to soil to supply plant nutrients. NPK = Nitrogen, Phosphorus, Potassium. Urea (highest N), DAP, MOP, superphosphate.
- Paints: Pigment + binder + solvent + additives. Protect surfaces; provide colour.
- Pigments: Coloured insoluble compounds. White (TiO₂), red (Fe₂O₃), blue (Prussian blue), yellow (chromates).
NDA tests common fertilizers (urea, DAP, NPK), and basic chemistry of paints.
Fertilizers and Nutrients
- Three primary nutrients (macronutrients): Nitrogen (N), Phosphorus (P), Potassium (K).
- Secondary nutrients: Calcium, Magnesium, Sulphur.
- Micronutrients: Iron, Manganese, Zinc, Copper, Boron, Molybdenum (needed in tiny amounts).
- Manure (organic): Cow dung, compost, vermicompost — slower release but improve soil structure.
- Chemical fertilizers deliver concentrated nutrients quickly but can damage soil microbiota with overuse.
Common Chemical Fertilizers
| Fertilizer | Formula | Nutrient | N content |
|---|---|---|---|
| Urea | CO(NH₂)₂ | Nitrogen | 46% — highest among nitrogen fertilizers |
| Ammonium Nitrate | NH₄NO₃ | Nitrogen | 33% |
| Ammonium Sulphate | (NH₄)₂SO₄ | Nitrogen + Sulphur | 21% N |
| Calcium Ammonium Nitrate (CAN) | 5Ca(NO₃)₂·NH₄NO₃·10H₂O | Nitrogen + Calcium | 25% |
| Superphosphate (Single) | Ca(H₂PO₄)₂ + CaSO₄ | Phosphorus | 16% P₂O₅ |
| Triple Superphosphate (TSP) | Ca(H₂PO₄)₂ | Phosphorus | 46% P₂O₅ |
| DAP (Diammonium phosphate) | (NH₄)₂HPO₄ | N + P | 18% N, 46% P₂O₅ |
| MOP (Muriate of Potash) | KCl | Potassium | 60% K₂O |
| NPK (composite) | various | N + P + K combined | e.g., 19:19:19 grade |
Paints
- Components:
- Pigment: Insoluble coloured solid (titanium dioxide white, iron oxide red).
- Binder (vehicle): Holds pigment to surface (oil, latex, polymers).
- Solvent (thinner): Keeps paint liquid for application (turpentine, water, mineral spirits).
- Additives: Driers, anti-skinning agents, mildewcides.
- Types:
- Oil paint: Pigment + linseed oil + thinner. Durable for outdoor. Slow drying.
- Emulsion (latex) paint: Pigment + water + acrylic polymer. Quick drying, low odour, common for interiors.
- Enamel paint: Solvent-based with high gloss. Metal surfaces, doors.
- Varnish: Transparent finish. Resin + solvent. Wood protection.
- Lacquer: Quick-drying transparent finish. Furniture, instruments.
- Distemper: Pigment + chalk + glue + water. Cheap interior paint.
- Whitewashing: Slaked lime [Ca(OH)₂] + water + chalk. Inexpensive surface coating; absorbs CO₂ to form CaCO₃.
Common Pigments
| Pigment | Compound | Colour |
|---|---|---|
| Titanium dioxide | TiO₂ | White (most common; replaced toxic lead-based paint) |
| Iron oxide | Fe₂O₃ | Red, brown (rust colours) |
| Lead chromate | PbCrO₄ | Yellow (toxic, phased out) |
| Chromium oxide | Cr₂O₃ | Green |
| Prussian blue | Iron ferrocyanide | Deep blue |
| Cadmium yellow / red | CdS / CdSe | Bright yellow/red (toxic, restricted) |
| Lampblack / Carbon black | Carbon | Black |
| Zinc oxide | ZnO | White (sunscreen) |
NDA PYQ Examples
Q: The nitrogen content of urea is approximately:
(a) 25% (b) 33% (c) 46% (d) 60%
Answer: (c) 46% — highest among nitrogen fertilizers.
Q: DAP fertilizer contains:
(a) Only nitrogen (b) Only phosphorus (c) Nitrogen and phosphorus (d) Potassium and sulphur
Answer: (c) Diammonium phosphate — N + P.
Q: NPK in fertilizers refers to:
(a) Nitrogen, Phosphorus, Calcium (b) Nitrogen, Phosphorus, Potassium (c) Nitric, Phosphoric, Potassium (d) Natural Plant Kit
Answer: (b) Nitrogen, Phosphorus, Potassium.
Q: Whitewash on walls turns hard because:
(a) Water evaporates (b) Ca(OH)₂ absorbs CO₂ to form CaCO₃ (c) It freezes (d) It oxidises
Answer: (b) Ca(OH)₂ + CO₂ → CaCO₃ + H₂O — solid layer.
Q: Titanium dioxide is the main pigment in:
(a) Red paint (b) White paint (c) Black ink (d) Blue dye
Answer: (b) White paint.
Drill Fertilizers and Paints for NDA
NDA-pattern items on Fertilizers and Paints with answer keys and explanations.
Start Free Mock TestFrequently Asked Questions
Why is urea the most popular nitrogen fertilizer?
Highest nitrogen content (46%) among common N fertilizers — so fewer bags need to be transported and applied. Also relatively cheap to manufacture (from ammonia and CO₂) and easy to handle. Most produced fertilizer globally.
What does '20-20-20 NPK' mean?
Percentages of N (20%), P₂O₅ (20%), and K₂O (20%) by weight in a balanced complete fertilizer. Different ratios suit different crops/stages (e.g., 19-19-19 general; 10-26-26 for fruiting).
Why is whitewashing common in India?
Cheap (slaked lime is plentiful), antibacterial (high pH kills microbes), reflective (cools houses in summer), absorbs CO₂ from air to form hard CaCO₃ over weeks. Annual or biennial application — cultural tradition + practical advantages.
Are lead-based paints still used?
No, banned or restricted in most countries since the 1970s-80s. Lead is highly toxic, especially for children — causes developmental disorders. Replaced by TiO₂ for white, organic pigments for colours.
Why do paints have a smell?
Solvent-based paints contain volatile organic compounds (VOCs) that evaporate as paint dries. VOCs can be harmful — modern 'low-VOC' or 'zero-VOC' water-based paints (latex/emulsion) are preferred for indoor use.