• Strong electrolytes
Strong electrolytes are substances that are virtually fully ionized in solution, and include ionic solids and strong acids. As a result of their complete ionization, the concentration of ions in solution is proportional to the concentration of strong electrolyte added.

eg. NaCl, KNO₃, HCl in aqueous solutions

• Weak electrolytes
Weak electrolytes are not fully ionized in solution. They include weak Bronsted acids and bases.

eg. CH₃COOH, NH₃, H₂O

• Non-electrolytes
Liquids/solutions that do not contain ions are referred as non electrolytes. They do not conduct electricity.

eg. C₆H₆, Kerosene

Conductance and conductivity

A metal cuboid is shown on the left hand side above. A cuboid shape portion of a solution with the similar dimensions of the metal cube which is in between two electrodes is shown on the right hand side.

Here l = Length of the metal cube or the selected cuboid shape portion of the solution (m)
A = Area of cross section (m₂)
R = Resistance (Ω )
ρ= Resistivity (Ωm )
1/R = Conductance ( Ω^-1 or S )

Regarding the above cuboids,

R∝l     and    R∝ (1/A)

∴ R∝(l/A)

R = ρl/A

ρ = RA/l

k =1/ρ = l/AR

• Coherent SI unit of conductivity is and the most practical unit is Ω^-1m^-1

• Conductivity and resistivity are constants for the particular substance (metal or solution with a given concentration) and it changes with temperature (about 2% per one degree Celsius in solution).

Factors affecting conductivity of a solution

• Nature of the solute (aqueous solutions of strong, weak and non electrolytes, molten electrolytes)
• Concentration of the solute
• Temperature

• For dilute solutions decrease in conductivity is approximately proportional to the concentration and this is very correct for very dilute solutions. The reason is the decrease of interactions among ions in dilution.

• Current = Charge / Time.
Current carried by an ion at a given temperature in a given electric field depends on the concentration of ions and their speed. Speed of an ion depends on its charge, size and potential gradient of the applied electric field.

• H⁺ and OH^– ions have the highest speeds. So those ions contributes a lot for the conductance. For example, H⁺ ions contribute about 80% for the conductance of dilute HCl solution.