How ionic solutions carry current. Resistance and conductivity, molar conductivity and how it changes with concentration, and Kohlrausch's law for strong and weak electrolytes.
3 lessons, about 1 h 30 min3 simulations11 problems6 practice questionsPython in every lesson
Created by StemPy LabA lamp lights when a salt solution joins two wires, but not when they dip in distilled water. The ions carry the current, and a conductivity cell measures how well they do it. The conductivity of a solution is the cell constant divided by the resistance, and a solution of known conductivity gives the cell constant.
When you dilute a salt solution, its conductivity falls, because fewer ions are left in each cubic metre. To compare electrolytes fairly we divide by the concentration. This gives the molar conductivity. It rises a little on dilution for a strong electrolyte and a great deal for a weak one.
In a very dilute solution every ion moves on its own, so each ion adds its own share to the molar conductivity. This is Kohlrausch's law. It gives the limiting value for a weak electrolyte, where a graph cannot, and it leads to the degree of dissociation and the solubility of a salt that hardly dissolves.
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