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Metals and Non-metals — Question 13

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Questions 13

You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Answer

When copper vessels come into contact with moist carbon dioxide in the air, copper carbonate is formed that gets deposited as a green layer on the surface of these copper vessels and tarnishes them. The citric acid present in lemon or tamarind juice acts to neutralize the basic copper carbonate, effectively dissolving this layer. This restores the characteristic luster of the copper vessels.

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Science | Chapter 3: Metals and Non-MetalsWeb Content

Chapter 3: Metals and Non-Metals — Quick Revision Guide

Introduction

Metals and non-metals have contrasting physical and chemical properties. This chapter covers their properties, reactivity series, ionic bonding, extraction of metals from ores, and corrosion prevention.

Key Points at a Glance

  1. Metals: lustrous, malleable, ductile, good conductors, sonorous, high m.p./b.p. Exceptions: Hg (liquid), Na/K (soft), Na/K/Li (low density)
  2. Non-metals: dull, brittle, poor conductors, low m.p./b.p. Exceptions: iodine (lustrous), diamond (hardest), graphite (conductor)
  3. Metals react with O2 (basic oxides), H2O, dilute acids, and salt solutions based on reactivity
  4. Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > ... > H > Cu > Ag > Au
  5. Ionic bonding: electron transfer from metal to non-metal; ionic compounds have high m.p., are hard, brittle, conduct electricity when molten/dissolved
  6. Extraction depends on reactivity: high (electrolysis), medium (reduction with C), low (heating in air)
  7. Thermite reaction: Fe2O3 + 2Al → 2Fe + Al2O3 (railway welding)
  8. Electrolytic refining: anode = impure, cathode = pure, electrolyte = metal salt solution
  9. Alloys: brass (Cu+Zn), bronze (Cu+Sn), stainless steel (Fe+Cr+Ni+C), solder (Pb+Sn); improve properties

Real-World Connections

Gold/silver jewellery uses alloys for hardness; galvanised iron sheets resist rusting; aluminium foil for food packaging; copper wiring in electrical circuits; stainless steel utensils resist corrosion.

Quick Self-Test (5 Questions)

  1. What is the most important concept you learned from this chapter?
  2. Can you write three key equations/formulae from this chapter from memory?
  3. Draw a labelled diagram relevant to this chapter without looking at your notes.
  4. Explain one real-world application of a concept from this chapter.
  5. What is one common mistake students make in this chapter, and how can you avoid it?

Further Study

  • NCERT Textbook Chapter 3
  • NCERT Exemplar Problems
  • Bright Tutorials Detailed Notes: ch03-metals-non-metals.html
  • Bright Tutorials Practice Questions: ch03-metals-non-metals.html
  • Previous Year CBSE Board Papers

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