UPSC Prelims 2007 Q121: Science & Technology – Chemistry
Which one of the following is called Philosopher’s wool?
- (a) Zinc Bromide
- (b) Zinc Nitrate
- (c) Zinc Oxide
- (d) Zinc Chloride
Answer: (c) Zinc Oxide
Explanation
Philosopher's wool = Zinc oxide (ZnO)
| Name | Compound |
|---|---|
| Philosopher's wool | Zinc oxide (ZnO) — forms as white woolly flakes when zinc burns in air |
| Chinese white / Zinc white | Also ZnO (as a paint pigment) |
| White vitriol | Zinc sulphate (ZnSO₄·7H₂O) |
| Blue vitriol | Copper sulphate (CuSO₄·5H₂O) |
| Green vitriol | Ferrous sulphate (FeSO₄·7H₂O) |
Uses of ZnO: sunscreens (blocks UV), ointments (calamine), rubber, paints.
Answer: (c) Zinc Oxide.
Why each option is right or wrong
- (a) Incorrect. Zinc bromide has no such common name.
- (b) Incorrect. Zinc nitrate is not called philosopher's wool.
- (c) CORRECT. Zinc oxide is called philosopher's wool (also Chinese white).
- (d) Incorrect. Zinc chloride is used as a flux and wood preservative.
Key point
Philosopher's wool = ZnO = Chinese white. White vitriol = ZnSO₄.
Remember
Philosopher's wool is zinc oxide.
Common mistakes
- Confusing white vitriol (zinc sulphate) with philosopher's wool (zinc oxide).
- Not linking 'wool' to the fluffy white flakes formed when zinc burns.
- Mixing up the three vitriols — blue (Cu), green (Fe), white (Zn).
Exam tip
Burn zinc → fluffy white 'wool' → ZnO.
Sources
- NCERT Class X — Science, Ch 3 (Metals and Non-metals)
- NCERT Class XII — Chemistry, Ch 8 (d- and f-Block Elements)