Introduction :

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

1.  The conversion of electrical energy into chemical energy
2.  The conversion of chemical energy into electrical energy

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

1. Insulators
2. 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 :