Conductors and Non Conductors
• Non-Conductors: Those substances which do not allow electric current to pass through them are called non-conductors or insulators. Example: - wood, plastic glass, rubber etc.
• Conductors: Those substances which allow electric current to flow through tem are called conductors. Examples: Copper, Iron, Gold, Silver, Graphite, salt solution etc.
Conductors can further be divided into two groups
• Metallic Conductors: These conductors conduct electricity or electric current by movement of electrons without undergoing any chemical change during the process. These conduct electricity in both solid as well as molten state. Example: All the metals and Graphite
• Electrolytes: Those substances which conduct electricity only when they are present in aqueous solution and not in solid form are called electrolytes. These conduct electricity by movement of ions in solutions.
Comparison of Electrolytic and Metallic Conduction
Electrolytic Conductance:
Specific Resistance or resistivity (ρ):
R = ρ× l /A
Where,
R = Resistance
A=Area of cross sections of electrodes
l = Distance between the electrodes.
Specific Conductance or Conductivity (κ):
κ = 1/ ρ
Units: W–1 cm–1 or Sm–1
Equivalent Conductance (Λ):
Conducting power of all the ions produced by one g-equivalent i.e. one equivalent of an electrolyte in a given solution
Λ = 1000 κ /C
Where, C be the normality of solution i.e. concentration of electrolytic solution in equivalent/L.
Units: W–1cm2
Molar Conductance (Λm):
Conductance of solution due to all the ions produced by one mole of the dissolved electrolyte in a given solution.
Λm = κ/c
Where, c = concentration of solution in mol m-3.
Λm = κ×1000/M
Where, M is molarity of solution.
Units: S cm2 mol-1
Relation between Λ and Λm
Λm = n Λ
Where n = n-factor of the electrolyte = total charge carried by either ion = M/E solution.
Molar and Equivalent Conductance: Increases with increase in dilution.
• Weak electrolyte: Increase is due to increase in extent of ionization.
• Strong electrolyte: Increase is due to increase in mobility of ions because of decreased inter-ionic attraction.
Debye-Hückel-Onsager Equation
Λm = Λ0m – (A+B Λ0m) √C
Where,
A & B = Debye-Hückel constants.
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