Questions 12
Give reasons :
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphides ores are usually converted into oxides during the process of extraction.
(a) Platinum, gold and silver are low reactive metals so they rarely corrode and hence do not lose their shine and lustre. Additionally, they are very malleable and ductile so they can be easily crafted into beautiful jewellery having fine design.
(b) Sodium, potassium and lithium react so vigorously with oxygen that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are stored under oil.
(c) Aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide on its surface. This oxide layer is very stable and acts as a protective coating by preventing further reaction of aluminium. This combined with aluminium's excellent heat conductivity, easy and cheap availability, malleability and ductility makes it a good choice to make utensils for cooking.
(d) As metals can be easily extracted by the reduction of their oxides rather than from their carbonates and sulphides therefore carbonate and sulphide ores are usually converted into oxides during the process of extraction.
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
- Metals: lustrous, malleable, ductile, good conductors, sonorous, high m.p./b.p. Exceptions: Hg (liquid), Na/K (soft), Na/K/Li (low density)
- Non-metals: dull, brittle, poor conductors, low m.p./b.p. Exceptions: iodine (lustrous), diamond (hardest), graphite (conductor)
- Metals react with O2 (basic oxides), H2O, dilute acids, and salt solutions based on reactivity
- Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > ... > H > Cu > Ag > Au
- Ionic bonding: electron transfer from metal to non-metal; ionic compounds have high m.p., are hard, brittle, conduct electricity when molten/dissolved
- Extraction depends on reactivity: high (electrolysis), medium (reduction with C), low (heating in air)
- Thermite reaction: Fe2O3 + 2Al → 2Fe + Al2O3 (railway welding)
- Electrolytic refining: anode = impure, cathode = pure, electrolyte = metal salt solution
- 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)
- What is the most important concept you learned from this chapter?
- Can you write three key equations/formulae from this chapter from memory?
- Draw a labelled diagram relevant to this chapter without looking at your notes.
- Explain one real-world application of a concept from this chapter.
- 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