Introduction to NCERT Exemplar Solutions for Class 12 Chemistry Chapter 6: General Principles and Processes of Isolation of Elements
Metals and non-metals that we use in everyday life are rarely found in their pure state. Instead, they exist in nature as minerals and ores combined with other elements. The process of obtaining pure metals from these ores is called metallurgy, and it plays a central role in industrial Chemistry. Chapter 6 introduces students to the scientific principles and practical steps involved in the extraction and refining of elements. The Class 12 NCERT Exemplar Solutions for this chapter provide detailed explanations of challenging problems that test understanding, logical application, and problem-solving ability. Also, solve questions of NCERT with the help of NCERT solutions for class 12 Chemistry.
Occurrence of Metals
Elements occur in nature either in a native state or in the combined state. Noble metals like gold, silver, and platinum are found in free form, while most other metals are present as oxides, sulfides, halides, or carbonates. Exemplar questions often test students on identifying ores of common metals such as hematite, bauxite, cinnabar, and chalcopyrite. This lays the foundation for understanding the extraction process.
Concentration of Ores
Before metals can be extracted, ores must be concentrated to remove impurities known as gangue. Different physical and chemical methods are used depending on the nature of the ore. Techniques include:
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Hydraulic washing for density-based separation
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Magnetic separation for ores attracted to magnets
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Froth flotation for sulfide ores
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Leaching for ores like bauxite using chemical solutions
Exemplar problems challenge students to decide which concentration method is most suitable for a given ore, ensuring that they learn to apply theoretical knowledge in a practical context.
Extraction of Crude Metal
Once concentrated, ores are converted to crude metals using pyrometallurgical, hydrometallurgical, or electrometallurgical processes. This involves roasting (heating in presence of oxygen) or calcination (heating in absence of oxygen) to convert ores into oxides, which can then be reduced using carbon, carbon monoxide, or more reactive metals.
Electrolytic reduction is also studied, especially for highly reactive metals like aluminum. Exemplar questions often ask students to compare reduction techniques and explain why a particular method is used for a specific metal.
Thermodynamic and Electrochemical Principles
The extraction of metals is governed by thermodynamic principles, particularly the Gibbs free energy change. The Ellingham diagram is introduced to show the feasibility of reduction reactions at different temperatures. Students also learn how electrochemical principles are applied in extraction processes, such as in the electrolytic refining of copper or aluminum.
Exemplar solutions provide practice in interpreting Ellingham diagrams, solving Gibbs free energy problems, and applying electrochemical equations to predict reaction feasibility. These higher-level questions help learners develop strong reasoning skills.
Refining of Metals
Metals obtained in crude form are impure and must be refined for industrial use. Different methods include:
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Electrolytic refining (used for copper, silver, gold)
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Zone refining (for high-purity silicon and germanium)
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Vapour-phase refining (such as Mond’s process for nickel and van Arkel process for zirconium)
The NCERT Exemplar questions provide detailed explanations of these refining methods, including why specific techniques are chosen for certain metals.