Key Concepts
- 1What is an alloy?
- 2What is corrosion?
Important Formulas & Facts
Homogeneous mixture of metals (or metal + non-metal). Examples: Brass (Cu+Zn), Bronze (Cu+Sn), Steel (Fe+C), Stainless Steel (Fe+Cr+Ni+C). Alloys are harder and more corrosion-resistant than pure metals.
Slow degradation of metals by chemical reaction with environment. Iron rusting: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O. Prevention: painting, oiling, galvanising, alloying, electroplating.
Must-Know Questions
Q1Which of the following metals is the most reactive?
Potassium (K) is the most reactive metal among the options. The reactivity series (descending): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au. Potassium reacts violently with cold water.
Q2An element reacts with oxygen to give a compound with a high melting point. This compound is soluble in water. The solution turns red litmus blue. The element is likely to be:
The compound has a high melting point (ionic), is soluble in water, and its solution is basic (turns red litmus blue). This describes a metal oxide (e.g., Na₂O, CaO). Metals form basic oxides. The element is calcium — CaO + H₂O → Ca(OH)₂ (basic).
Q3What are amphoteric oxides? Give two examples.
Amphoteric oxides are metal oxides that react with both acids and bases to form salt and water. They show both acidic and basic behaviour. Examples: 1. Aluminium oxide (Al₂O₃): Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O (reacts with acid) Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (reacts with base) 2. Zinc oxide (ZnO): ZnO + 2HCl → ZnCl₂ + H₂O (reacts with acid) ZnO + 2NaOH → Na₂ZnO₂ + H₂O (reacts with base)
Q4Why is sodium kept immersed in kerosene oil?
Sodium is a highly reactive metal that reacts vigorously with oxygen in air and with water. In air, it forms sodium oxide (4Na + O₂ → 2Na₂O), and with water it forms NaOH and H₂ with explosive violence (2Na + 2H₂O → 2NaOH + H₂↑ + Heat). To prevent it from catching fire or reacting with moisture, sodium is stored under kerosene oil, which does not react with sodium and prevents contact with air and water.
Q5Define the terms: (a) Mineral (b) Ore (c) Gangue
(a) Mineral: The naturally occurring compounds or elements of metals found in the earth's crust are called minerals. Example: Bauxite (Al₂O₃·2H₂O), haematite (Fe₂O₃). (b) Ore: A mineral from which a metal can be extracted profitably and conveniently is called an ore. All ores are minerals but all minerals are not ores. Example: Bauxite is the ore of aluminium. (c) Gangue: The unwanted impurities (sand, rocky matter, earthy particles) present in an ore are called gangue. It is removed during the concentration of ore.
Practice Metals and Non-metals
Reinforce what you just revised with practice questions