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Conductance of Electrolytic Solutions

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Conductance of Electrolytic Solutions - Lesson Summary

Resistivity (ρ) is defined as the electrical resistance when a sample is 1metre long with a cross-section of 1square metre. Resistivity is measured in ohm-metres.

R = ρ l/A

If l = 1m and A = 1m2
R = ρ 1m/1m2
  R = ρ

Conductivity (κ) is the conductance of a material when it is 1metre long with a cross section of 1square metre. Conductivity is measured in S m-1.

G = K A/l

If l = 1m and A = 1m2
G = K 1m2/1m
G = K

Materials can be classified as conductors, non-conductors and semiconductors based on their conductivity.

Conductors are materials with large conductivities such as metals and metal alloys.

Some non-metals including graphite, Carbon black and some organic polymers are also electrical conductors.

Insulators are materials with very low conductivity such as glass and ceramics.

Semi-conductors have conductivities between conductors and insulators.

Superconductors have zero resistivity (or) infinite conductivity. The earliest materials identified as superconductors were metals and alloys at low temperatures below 15K.

The conductivity of electricity by ions present in a solution is called electrolytic conductance.

Molar conductivity is the conductivity of a solution divided by the molarity of the solution. Limiting molar conductivity is the conductivity at infinite dilution.

λm = K/C

If C is in mol m-3
   k is in Sm-1
Unit of λm = Sm2mol-1

λm (Sm2mol-1) = K(Sm-1) x 1000(Scm3L-1)/molarity(mol L-1)

Conductivity meters can be used to measure the conductivity and molar conductivity of an aqueous electrolyte solution by comparing to a solution of known conductivity.

The molar conductivities of strong electrolytes are weakly dependent on concentration. Molar conductivities of weak electrolytes are very dependent on concentration.

Kohlrausch's law states that the limiting molar conductivity of an electrolyte can be determined from the sum of the individual contributions from the ions in the electrolyte. Equilibrium constants for weak electrolytes can be determined from conductivity data.


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