Class 12 Chemistry Electrochemistry Electrical conductance

Electrical conductance

  • The inverse of resistance is known as conductance.

  • It is measured in a unit called Siemens represented by the symbol ‘S’
  • It is equal to ohm–1 also known as mho or Ω –1.
  • The electricalconductance depends on:
    Nature and structure of the metal
    2. Number of valence electrons per atom
    3. Electrical conductance decreases with increase of temperature and vice versa.

  • The free ions Na+ and Cl- present in the solution are responsible for the conductance in a solution.
  • The inverse of resistivity is termed as conductivity.
  • Ω = 1/k
  • It is represented by the symbol (Greek, kappa).
  • It is measured in a unit called Sm–1.
  • When length = 1m.

Cross sectional area = 1m2

            Then conductivity becomes the conductance.

The conductivity of an electrolytic solution depends on:

1.Nature of the electrolyte added
2.Size of the ions produced and their solvation
3.Nature of the solvent and its viscosity
4.Concentration of the electrolyte
5.It increases with the increase of temperature.
6.Pressure

 

  • Matters can be classified into conductors, insulators andsemiconductors depending on the magnitude of their conductivity.

Conductors:

  • Solids with conductivities ranging between 104 to 107 ohm–1m–1 are conductors.
  • Metals have conductivities in the order of 107 ohm–1m–1 is good conductors.
  • For example, Iron, Copper, Aluminum.

Fig. Metal is used at the tip of the plug that is inserted into the socket

 

Insulators:

  • Solids with very low conductivities ranging between 10–20 to 10–10 ohm–1m–1.
  • For example, Wood, plastic, cloth, glass.

 

Fig. Wood and plastics are also solids but are insulators

A man touching the electric pole with a metal rod will get an electric shock because metal rod is a conductor whereas a man touching the same with a wooden plank will be safe because wood is an insulator.

Semiconductors:

  • Solids with conductivities in the intermediate range from 10–6 to 104 ohm–1 m–1.
  • For example, Gallium, Germanium, Silicon

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