CBSE Class 12 Chemistry Chapter 6: General Principles and Processes of Isolation of Elements NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 12 PDF

This chapter delves into the fundamental principles and various processes involved in the isolation of elements from their naturally occurring sources. The NCERT Solutions for Class 12 Chemistry, Chapter 6, cover key concepts such as the abundance of elements, the role of thermodynamics and chemical kinetics in extraction, and different methods like hydrometallurgy, pyrometallurgy, and electrometallurgy. It also explains specific extraction processes for metals like aluminium, copper, and iron, along with purification techniques like distillation, liquation, electrolysis, and zone refining. These solutions provide clear explanations and step-by-step problem-solving, crucial for understanding the complex metallurgical processes and preparing effectively for exams.

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Quick info

Board	CBSE
Class	Class 12
Subject	Chemistry Exemplar
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 6

Chapter summary

Chapter 6 of the NCERT Class 12 Chemistry textbook focuses on the general principles and processes used for isolating elements. The NCERT Solutions cover the abundance of elements in the Earth's crust, thermodynamic principles of metal extraction (like Ellingham diagrams), and kinetic considerations. It details various methods including extraction by chemical reduction, electrolysis, and specific processes for obtaining metals like copper, aluminium, and iron. Purification techniques are also discussed, offering a comprehensive overview of metallurgy.

Learning outcomes

Understand the abundance of elements in the Earth's crust.
Explain the thermodynamic and kinetic principles governing metal extraction.
Describe various methods of metal extraction, including reduction and electrolysis.
Illustrate specific extraction processes for common metals.
Identify and explain purification techniques for metals.

Topics covered

Paper topics

Abundance of Elements
Thermodynamic Principles of Metallurgy
Ellingham Diagrams
Kinetic Considerations in Metallurgy
Extraction by Chemical Reduction
Extraction by Electrolytic Reduction
Hydrometallurgy
Pyrometallurgy
Electrometallurgy
Purification of Metals
Distillation
Zone Refining

Important topics

Thermodynamic Principles of Metallurgy
Ellingham Diagrams
Extraction by Chemical Reduction
Extraction by Electrolytic Reduction
Purification of Metals
Zone Refining

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Questions and Solutions

Multiple Choice Questions (MCQs) - Question 1

In the extraction of chlorine by electrolysis of brine, which of the following statements is correct?

Oxidation of Cl⁻ ion to chlorine gas occurs.
Reduction of Cl⁻ ion to chlorine gas occurs.
For the overall reaction, ΔG° has a negative value.
A displacement reaction takes place.

Solution: The extraction of chlorine by the electrolysis of brine involves the following reaction at the anode:

$2Cl^-(aq) \rightarrow Cl_2(g) + 2e^-$

This clearly shows the oxidation of Cl⁻ ions to chlorine gas. The overall reaction is:

$2H_2O(l) + 2Cl^-(aq) \rightarrow H_2(g) + Cl_2(g) + 2OH^-(aq)$

The standard Gibbs free energy change (ΔG°) for this reaction is approximately +422 kJ, indicating it is not thermodynamically feasible without external energy input. The standard electrode potential (E°) can be calculated using

\Delta G^{\circ} = -nFE^{\circ}

, which results in

E^{\circ} = -2.2V

. Therefore, an external potential greater than 2.2V is required for the reaction to proceed. Thus, option (a) is correct.

Multiple Choice Questions - Question 2

When copper ore is mixed with silica and heated in a reverberatory furnace, copper matte is produced. What does the copper matte contain?

Sulphides of copper (II) and iron (II)
Sulphides of copper (II) and iron (III)
Sulphides of copper (I) and iron (II)
Sulphides of copper (I) and iron (III)

Solution: In the process of smelting copper ore with silica in a reverberatory furnace, iron is removed as slag (silicate), and the remaining molten mixture is called copper matte. This copper matte primarily consists of sulphides of copper(I) and iron(II). The chemical composition is typically represented as

Cu_2S

and

FeS

Multiple Choice Questions - Question 3

Which of the following reactions is an example of autoreduction?

$Fe_3O_4 + 4CO \longrightarrow 3Fe + 4CO_2$
$Cu_2 O + C \longrightarrow 2Cu + CO$
$Cu^{2+} (aq) + Fe(s) \longrightarrow Cu(s) + Fe^{2+} (aq)$
$Cu_2 O + \frac{1}{2} Cu_2 S \longrightarrow 3Cu + \frac{1}{2} SO_2$

Solution: Autoreduction, also known as self-reduction, occurs when a metal oxide is reduced by its own sulphide. In the given options, the reaction

Cu_2O + \frac{1}{2}Cu_2S \longrightarrow 3Cu + \frac{1}{2}SO_2

exemplifies autoreduction. Here, copper(I) oxide (

Cu_2O

) is reduced by copper(I) sulphide (

Cu_2S

) to yield metallic copper. This process is often used to produce blister copper.

Multiple Choice Questions - Question 4

A number of elements are available in the Earth's crust, but which of the following are the most abundant elements?

Al and Fe
Al and Cu
Fe and Cu
Cu and Ag

Solution: Among the elements found in the Earth's crust, Aluminium (Al) is the third most abundant element, constituting about 8.3% by weight. Iron (Fe) is the fourth most abundant, making up approximately 4.2% by weight. While copper (Cu) and silver (Ag) are also present, their abundance is significantly lower compared to aluminium and iron.

Multiple Choice Questions - Question 5

Zone refining is based on which principle?

Impurities of low boiling metals can be separated by distillation.
Impurities are more soluble in molten metal than in solid metal.
Different components of a mixture are differently adsorbed on an adsorbent.
Vapours of volatile compound can be decomposed into pure metal.

Solution: Zone refining is a purification technique that relies on the difference in solubility of impurities between the solid and molten states of a metal. The principle is that impurities are generally more soluble in the molten metal than in the solid metal. In this method, a molten zone is created using a heater, which moves along an impure metal rod. As the molten zone moves, impurities preferentially dissolve in it and are carried along, leaving behind purer metal that crystallizes out. This process is repeated to achieve high purity, commonly used for refining elements like germanium and silicon.

Common mistakes

Confusing oxidation and reduction steps in electrolysis.
Incorrectly applying thermodynamic feasibility to practical extraction.
Misidentifying the composition of intermediate products like copper matte.
Confusing different purification methods and their underlying principles.

Revision tips

Focus on understanding the core principles behind each extraction method.
Memorize the key reactions and conditions for isolating common metals.
Pay close attention to the role of thermodynamics (e.g., Ellingham diagrams) and kinetics.
Review the purification techniques and the specific impurities they remove.

Practice MCQs

Q1. In the electrolytic extraction of chlorine from brine, which process occurs?

Q2. What is the primary composition of copper matte produced when copper ore is mixed with silica in a reverberatory furnace?

Q3. Which of the following reactions is an example of autoreduction?

Q4. Which are the two most abundant elements in the Earth's crust among the given options?

Q5. The principle behind zone refining is based on which property?

Frequently asked questions

What is the main focus of Chapter 6 in CBSE Class 12 Chemistry?

Chapter 6 focuses on the general principles and processes involved in the isolation and purification of elements from their natural sources, covering metallurgical concepts.

What are the key principles behind metal extraction discussed in these solutions?

The solutions explain extraction based on thermodynamic feasibility (using Ellingham diagrams) and kinetic factors, as well as various chemical and electrochemical reduction methods.

How do these NCERT Solutions help in exam preparation?

These solutions provide clear, step-by-step explanations for complex metallurgical processes and MCQs, helping students understand concepts and practice problem-solving for exams.

What is autoreduction, and can you give an example?

Autoreduction is a process where a metal oxide is reduced by its corresponding sulphide. An example is the reaction of copper(I) oxide with copper(I) sulphide to produce copper.

What is the principle of zone refining?

Zone refining is based on the principle that impurities are more soluble in the molten state of a metal than in its solid state. This allows impurities to be concentrated in a molten zone that moves through the metal rod.

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