Science Class 12 - General Principles-And-Processes-Of-Isolation-Of-Elements Notes

Comprehensive study notes for Class 12 - General Principles-And-Processes-Of-Isolation-Of-Elements olympiad preparation

General Principles and Processes of Isolation of Elements

Welcome to the chapter on General Principles and Processes of Isolation of Elements for Class 12. In this chapter, you will learn about the various methods used to extract and purify metals from their ores. By the end of this chapter, you will understand the basic concepts of metallurgy and the steps involved in the isolation of elements from natural sources.

Introduction

Most metals are found in nature as compounds, not in their pure form. The process of obtaining pure metals from their ores is called metallurgy. This chapter covers the important steps and principles involved in the extraction and purification of metals.

Key Concepts

  • Ore: A naturally occurring substance from which a metal can be profitably extracted.
  • Gangue: The unwanted impurities present in the ore.
  • Metallurgy: The process of extraction of metals from their ores and their purification.

Steps in Metallurgy

  • 1. Concentration of Ore: Removal of gangue from the ore using physical or chemical methods (e.g., gravity separation, froth flotation, magnetic separation).
  • 2. Extraction of Metal: The concentrated ore is converted into the metal by chemical processes such as reduction (using carbon, electrolysis, or other reducing agents).
  • 3. Purification of Metal: The crude metal obtained is purified by methods like distillation, liquation, electrorefining, or zone refining.

Important Methods of Concentration

  • Gravity Separation: Used when the ore particles are heavier than the gangue.
  • Froth Flotation: Used for sulphide ores. The ore is mixed with water and chemicals to form froth, which carries the ore particles to the surface.
  • Magnetic Separation: Used when either the ore or the gangue is magnetic.

Extraction of Crude Metal

  • Calcination: Heating the ore in the absence of air to remove volatile impurities.
  • Roasting: Heating the ore in the presence of air to convert sulphides to oxides.
  • Reduction: Converting metal oxides to metals using reducing agents like carbon, CO, or by electrolysis.

Purification of Metals

  • Electrolytic Refining: The impure metal is made the anode and pure metal is deposited at the cathode.
  • Zone Refining: Used for highly pure metals. A moving heater melts a small region, carrying impurities with it.
  • Distillation and Liquation: Used for metals with low boiling or melting points.

Applications and Importance

  • Metallurgy is essential for obtaining pure metals for industrial use.
  • Understanding extraction helps in recycling and conservation of resources.

Practice Questions

  1. What is the difference between ore and gangue?
  2. Describe the froth flotation process.
  3. Why is calcination used in metallurgy?
  4. Explain electrolytic refining with an example.
  5. Name two methods used for the purification of metals.

Challenge Yourself

  • Draw a flowchart showing the steps involved in the extraction of a metal from its ore.
  • Research and write about the extraction of aluminium from bauxite.

Did You Know?

  • Gold is often found in its native (pure) form, while most other metals are found as compounds.
  • Zone refining is used to obtain ultra-pure silicon for making computer chips.

Glossary

  • Ore: A mineral from which a metal can be extracted profitably.
  • Gangue: The unwanted material present in the ore.
  • Calcination: Heating an ore in the absence of air.
  • Roasting: Heating an ore in the presence of air.
  • Electrolytic Refining: Purification of metal using electricity.

Answers to Practice Questions

  1. Ore is a mineral from which metal can be extracted; gangue is the unwanted material in the ore.
  2. Froth flotation is a process used to concentrate sulphide ores by mixing them with water and chemicals to form froth, which carries the ore particles to the surface.
  3. Calcination is used to remove volatile impurities from the ore by heating it in the absence of air.
  4. In electrolytic refining, impure metal is made the anode, pure metal is deposited at the cathode (e.g., copper refining).
  5. Zone refining, electrolytic refining, distillation, liquation (any two).

Understanding metallurgy helps us extract and use metals wisely for the progress of society!