Question 15
Give a reason why –
(a) rust turns moist red litmus blue
(b) a green deposit is seen on the surface of an article of copper
(c) iron objects rust easily but the iron pillar at Qutab Minar has not rusted over the years.
(a) Rust is hydrated iron [III] oxide. As all metallic oxides are basic in nature and rust is a metallic oxide of iron, hence, it turns moist red litmus blue.
(b) The green deposit on copper articles is caused by copper reacting with moisture and atmospheric gases to form copper carbonate [CuCO3], which is green, and copper hydroxide [Cu(OH)2].
(c) Iron pillar of Qutab Minar has not rusted over the years because
- The high purity and great mass of iron may have created a temperature stabilizer thus reducing the condensation of moisture on it.
- The protective passive iron coating formation on the surface of iron.
- Good forge welding and absence of impurities in iron.
ICSE Class VII Chemistry Chapter 5 14 Marks
Metals and Non-Metals — Quick Study Guide
Elements are broadly classified as metals, non-metals, or metalloids based on their physical and chemical properties.
Key Properties
- Metals: Lustrous, malleable, ductile, sonorous, good conductors, high density
- Non-metals: Dull, brittle, poor conductors, non-sonorous, low density
- Metalloids: Properties of both (e.g., Silicon, Germanium)
Chemical Reactions
- Metal + O2 → Basic oxide (turns red litmus blue)
- Non-metal + O2 → Acidic oxide (turns blue litmus red)
- Metal + Acid → Salt + H2
Exam Tips
- Know all exceptions: Mercury (liquid), Graphite (conducts), Diamond (lustrous), Na/K (soft)
- Learn the comparison table (8 properties) thoroughly
- Practice writing equations for metal reactions
- Know uses of at least 5 metals and 5 non-metals
Bright Tutorials | ICSE Class VII Chemistry | Chapter 5: Metals and Non-Metals | Contact: 9403781999