Introduction

Introduction :

Electrochemistry deals with the study of electrochemical processes and their applications which involve:

The conversion of electrical energy into chemical energy
The conversion of chemical energy into electrical energy

Based on electrical conductivity, the materials are divided into two types as follows:

Insulators
Conductors

Insulators :

The substances which resist the flow of electric current through them are called insulators.
They do not have free electrons or freely moving charged particles. e.g. Organic polymers (like plastics), glass, diamond, quartz etc.,

Conductors :

The substances which allow the flow of electricity through them with little resistance are known as conductors. These are divided into:

1. Metallic or electronic conductors :

Electrical conductors are materials which contain movable electric charge. The charge may be positive or negative. In case of metallic conductors like copper or aluminium, the movable charge particles are electrons and in electrolytic conduction the movable charge particles are ions, either positive ions or negative ions.

Electronic Conductors :

Electronic Conductors are the conductors which conduct the electricity through the electrons.
Example: All metals, Graphite etc.
These materials contain electrons which are relatively free to move.

Metallic Conductors :

Metallic Conductors are those which allow electricity to pass through them without undergoing any chemical change.
The conduction occurs due to the movement of electrons under the influence of applied electrical potential. The stream of electrons constitutes the current.
Conductivity decreases with increase in temperature due to vibrational disturbances.

2. Electrolytes :

The substances which furnish oppositely charged ions for the conduction of electricity.
Example : NaCl, KCl, $$CH_3COOH$$, HCl etc.
There is flow of ions towards the oppositely charged electrodes.
During conduction of electricity through electrolytes, oxidation occurs at anode whereas reduction occurs at cathode i.e., a chemical reaction occurs.
The conductivity increases with increase in temperature as the extent of ionization increases.
In order to pass the current through an electrolytic conductor (aqueous solution or fused electrolyte), two rods or plates (metallic conductors) are always needed which are connected with the terminals of a battery.
These rods or plates are known as
- Anode : The electrode through which the current enters the electrolytic solution is called the anode (positive electrode)
- Cathode: The electrode through which the current leaves the electrolytic solution is known as cathode (negative electrode).

The electrolytic solution conducts electricity not by virtue of the electrolytic as in metallic conductors but as a result of movement of charged particles called ions towards the respective oppositely charged electrodes.
The ions which carry positive charge and move towards cathode are termed cations while ions carrying negative charge which move towards anode are called
When these ions reach the boundary between a metallic and an electrolytic conductor, electrons are being either attached to or removed from the ions.
Removal of electrons is termed oxidation (de−electronation) which occurs at anode while addition of electrons is called reduction (electronation) that takes place at cathode.
Hence, flow of electrons through the outer circuit from anode to cathode across the boundary is accompanied by oxidation and reduction.
The electrolytes undergo dissociation to furnish ions either in molten state or in aqueous solutions.
Depending on the extent of ionization (or dissociation) in water, the electrolytes are further divided into:
- Strong electrolytes: Undergoes complete ionization in water.
  - Example: $$ NaCl, KCl, K_2SO_4, HCl, H_2SO_4, NaOH, NaNO_3.,$$
- Weak electrolytes : Undergoes partial ionization in water.
  - Example: $$HF, CH_3COOH, NH_4OH, HCOOH $$etc.
- Non-electrolytes: The substances which do not furnish ions for electrical conduction are called non-electrolytes.
  - Example : urea, glucose, sucrose, alcohol, glycerine, pure water etc.

Distinction between metallic and electrolytic conduction :

S No	Metallic conduction	Electrolytic conduction
1	Electric current flows by movement of electrons	Electric current flows by movement of ions
2	No chemical change occurs	Ions are oxidized or reduced at the electrodes
3	It does not involve the transfer of any matter	It involves transfer of matter in the form of ions.
4	Ohm's law is followed	Ohm's law is followed
5	Resistance increases with increase of temp.	Resistance decreases with increase of temp
6	Faraday law is not followed.	Faraday law is followed.

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Q1 : What is Electrochemistry?

Electrochemistry is defined as the branch of chemistry that examines the phenomena resulting from combined chemical and electrical effects.

Q2 : What is the difference between an insulator and a conductor?

Conductors are the substances which allow the electricity to pass through them while insulators resist electricity. A conductor is something which allows electric current to flow through it freely whereas an insulator prevents any electric current flowing through it.

Q3 : What are insulators and conductors of heat?

The materials which allow heat to pass through them easily are conductors of heat. For examples,aluminum, iron and copper. The materials which do not allow heat to pass through them easily are poor conductors of heat such as plastic and wood. Poor conductors are known as insulators.

Q4 : Is air a good insulator?

Yes, air is an excellent insulator. As air is mostly empty space, thermal energy does not transfer easily. This is why big, fluffy blankets with lots of trapped air are so warm

Q5 : Give some examples for Conductors and Insulators?

Examples of Conductors include metals, aqueous solutions of salts (i.e., ionic compounds dissolved in water), graphite, and the human body. Examples of Insulators include plastics, styrofoam, paper, rubber, glass, and dry air.

Q6 : Define Conductors and what are types of conductors?

Conductors : The substances which allow the flow of electricity through them with little resistance are known as conductors. These are divided into: 1. Metallic or electronic conductors : Electrical conductors are materials which contain movable electric charge. The charge may be positive or negative. In case of metallic conductors like copper or aluminium the movable charge particles are electrons and in electrolytic conduction the movable charge particles are ions, either positive ions or negative ions. Electronic Conductors : Electronic Conductors are the conductors which conduct the electricity through the electrons. Example: All metals, Graphite etc. These materials contain electrons which are relatively free to move. Metallic Conductors : Metallic Conductors are those which allow electricity to pass through them without undergoing any chemical change. The conduction occurs due to the movement of electrons under the influence of applied electrical potential. The stream of electrons constitutes the current. Conductivity decreases with increase in temperature due to vibrational disturbances.

Q7 : Define electrolyte?

An electrolyte is a chemical compound that ionizes when dissolved or molten and thus produces an electrically conductive medium. This includes most acids, salts and bases.

Q8 : What is Ion?

An atom or group of atoms (i.e. a radical) which has gained or lost one or more outer shell (valence) electrons, giving it a net positive or negative electrical charge. For Example: When sulfuric acid ($$H_2SO4$$) is added to water, it breaks down into $$H^+$$ and $$SO_4$$= ions according to $$H_2SO_4\rightarrow 2H^+ + SO^=_4$$ It thus breaks up into three ions — two $$H^+$$ ions and an $$SO^=_4$$ ion. Here the group of atoms representing the sulfate radical, $$SO^=_4$$ , has two extra electrons which it has stolen from the two hydrogen atoms, giving it a net negative charge of -2e.

Q9 : Define Electrolysis?

Electrolysis is the passage of an electric current through an electrolyte with subsequent migration of positively and negatively charged ions to the negative and positive electrodes and ensuing chemical changes.

Q10 : What is Electrolytic cell?

Electrolytic cell is a cell in which electrolysis occurs, consisting of an electrolyte through which current from an external source is passed, by a system of electrodes, in order to produce an electrochemical reaction.

Q11 : Define Anode?

(1) The positive electrode of an electrolytic cell. (2) The negative terminal of a voltaic or primary cell.

Q12 : Define Cathode?

(1) The negative electrode of an electrolytic cell. (2) The positive terminal of a voltaic or primary cell.

Q13 : What is Anion and Cation?

Anion is negatively charged ion where as Cation is positively charged ion

Q14 : Define Ionic compound?

An ionic compound is a compound formed by ions bonding together through electrostatic forces. Upon dissolving, it breaks apart into its individual ions. Ionic compounds are usually formed by a bonding of metal and non-metal ions. Example: table salt, NaCl.

Q15 : Describe the properties of ionic compounds?

Following are the properties shared by the ionic compounds. Notice that the properties of ionic compounds relate to how strongly the positive and negative ions attract each other in an ionic bond. • Ionic compounds form crystal lattices rather than amorphous solids. • Ionic compounds have high melting points and high boiling points. • Ionic compounds have higher enthalpies of fusion and vaporization than molecular compounds. • Ionic compounds are hard and brittle. • Ionic compounds conduct electricity when they are dissolved in water. • Ionic solids are good insulators.

Unit-1 Electrochemistry25

Unit-2 Chemistry of Batteries13