Maharashtra Board Class 12 Chemistry Chapter 5 Electrochemistry PDF Download

5. Electrochemistry

Can You Recall?

What is a redox reaction?

Which form of energy is converted into electrical energy in dry cells?

How is NaOH manufactured from NaCl?

5.1 Introduction

Dry cell is used to power our electrical and electronic equipments because it generates electricity. Do you know how does a dry cell generate electricity? A chemical reaction occurs in it which generates electricity. Thus in a dry cell chemical energy is converted into electrical energy.

You are familiar with the electrolysis of solutions of ions. Electrolysis is breaking down of an ionic compound by the passage of electricity. Breaking down of an electrolyte during electrolysis is a chemical reaction that takes place by the passage of electricity. Electrical energy is, thus, converted into chemical energy.

Electrochemistry is the area of chemistry which is concerned with interconversion of chemical and electrical energy.

It also deals with the resistance and conductance of aqueous electrolytic solutions. The determination of conductivities of aqueous electrolytic solutions provide an information on the extent of ionization of electrolytes in water. (Refer to Chapter 3).

The study of electrochemical cells is important in science and technology. It makes possible the manufacture of essential chemicals. You have learnt preparation of NaOH, widely used in the manufacture of soaps, detergents and paper, by electrolysis of NaCl. Electrolysis is possibly the only means to produce fluorine. The processes such as electro-refining (for purification of metals), electroplating (for coating one metal is on the surface of another) are also electrochemical processes.

In standard XI, you learnt redox reactions. Redox reaction forms the basis for the generation of electricity by chemical reactions and also for chemical reactions brought out by means of electricity. These processes are carried out in an electrochemical cell. Electrochemistry deals with the design and operation of such cells.

The current research in electrochemistry is focused on the design of fuel cells. The fuel cells are being explored as convenient and compact source of electricity.

Teacher's Note

Electrochemistry is used in our daily life. For example, batteries in mobile phones and torches work by electrochemical reactions. Like Aadhaar card stores information digitally, electrochemistry also converts chemical energy into electrical energy in a digital way through electrons.

Exam Trick

Remember: Electrochemistry = Chemical energy and Electrical energy going back and forth. In a battery, chemicals give electricity. In electrolysis, electricity makes chemicals. That is the whole chapter!

Points to Remember

Electrochemistry changes chemical energy into electrical energy and electrical energy into chemical energy.
Electrolysis breaks down ionic compounds using electricity.
Dry cells and batteries generate electricity through chemical reactions.
Metals like copper and zinc can be purified using electrochemistry.
Electrochemical cells have two parts: anode and cathode where reactions happen.

5.2 Electric Conduction

We know that the electric current represents a charge transfer. A charge transfer or flow of electricity occurs through substances called conductors. There are two types of conductors which give rise to two types of conduction of electricity.

5.2.1 Metallic Conduction

Can You Recall?

What is the origin of electrical conductivity of metals?

Electrical conduction through metals involves a direct flow of electrons from one point to the other. The outermost electrons of metals form conduction bond. The electrons in conduction band are free to move and hence flow under the influence of applied electrical potential (Chapter 1). Metallic conductors are, thus, electronic conductors.

Teacher's Note

Think about copper wire. When you connect it to a battery, electrons flow through it like water flows in a pipe. These electrons move from the negative side to the positive side of the battery, just like water flows from high to low places.

Exam Trick

Remember: Metallic conduction = electrons moving. It is called electronic conduction because electrons carry the charge. Easy!

Points to Remember

In metals, electrons are free to move and carry electric current.
Metallic conductors are also called electronic conductors.
The outermost electrons form a conduction band in metals.
Electrons flow from negative to positive through an external circuit.
Copper and aluminum are good metallic conductors.

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