Questions 15
A man went door to door posing as a goldsmith. He promised to bring back the glitter of the old and dull ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
The man's actions and the outcome suggest that he used aqua regia to clean the gold bangles. Aqua regia is a mixture of one part by volume of concentrated nitric acid and three parts by volume of concentrated hydrochloric acid. It is known for its ability to dissolve noble metals like gold and platinum.
When the man dipped the bangles in aqua regia, outer layer of gold dissolved in it. So, although the bangles sparkled like new but their weight was reduced drastically.
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