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ICSE Class 7 Chemistry Question 12 of 16

Metals and Non-metals — Question 11

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Question 11

Explain the term – rusting and give a word equation for the formation of rust. If polished iron nails are kept in three separate test tubes, state the contents in each test tube required, to prove the conditions for rusting.

Answer

Rusting involves slow oxidation of iron in presence of air and moisture resulting in formation of hydrated iron [III] oxide called rust.

Iron + Oxygen ⟶ Iron [III] Oxide →moisture\xrightarrow{\text{moisture}} Hydrated Iron [III] Oxide [rust]

 Test Tube ATest Tube BTest Tube C
ContentsAnhydrous calcium chlorideBoiled tap water with oil layer on topOrdinary tap water
Condition presentOxygenMoistureMoisture & oxygen
Condition absentMoistureOxygenNil
ResultIron nails do not rustIron nails do not rustIron nails rust
ConclusionMoisture is essential for rustingOxygen is essential for rustingMoisture and oxygen both are essential for rusting

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

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