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I learnt that on dilution of an electrolytic solution, it's conductivity decreases. However, there is an increase in the molar conductivity of the solution. The book explained the reason by comparing the definition of the two terms. However, it gave a hypothetical example which contradicts the statement it earlier stated. Maybe there is a printing error, but it has got me confused now.

Can someone please explain why the conductivity of an electrolytic solution decreases but molar conductivity increases on dilution, maybe with the help of a good hypothetical example?

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I've just been doing an experiment on this, and my understanding's not that great, but as I understand it the conductivity decreases because you have a lower concentration of charge carriers in the solution. The molar conductivity increases however, because as the charged ions get further apart they interact and slow each other down less. Essentially each ion becomes more able to move through the solution, but the increase in conductivity from this effect is outweighed by the decrease due to there being fewer ions in a given volume.

Personally I find it easier to think about the other way around. As you increase the concentration of the solution you get more charge carrying ions, so the conductivity increases. But because the ions get closer together they begin to interact and slow each other down so the conductivity per mole of the ions is reduced.

I hope you still find this useful and that I managed to explain what I meant

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  • $\begingroup$ I agree with the answer, but what will be the effect in resistance of a fairly concentrated solution of a strong electrolyte (say 2N $\ce{NaCl}$)? Will the resistance increase because of some unionized molecules of solute in high concentration? $\endgroup$ – Apurvium Jul 17 at 11:07

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