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When current is passed through a beaker of salt water, the ions move towards the terminals (based on their charge– e.g., sodium ions to the cathode and chlorine ions to the anode).

Following this idea, should there not be a certain point when all the positive ions are on one side, and the negative on the other– with no further movement? So, in effect, causing the solution to not be conductive to electricity anymore?

EDIT: Would this be apparent if I were to do an experiment?

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No, all water has a small spontaneous rate of generating ion pairs. There is a fresh supply of ions generated as long as there is water, so it is only when the water all leaves the system that conduction stops.

What an electric current does, is shift the equilibrium concentration due to that spontaneous generation, so that there is excess (OH-) ions around the positive terminal, and excess (H3O+) ions around the negative terminal. There may (or may not) be a reaction AT those terminals, creating some chemical substances other than water and the electrode material. Some generation of peroxide or hydrogen gas is certainly possible.

The concentration of those ions is represented by the pH of the water: near the positive terminal (anode) the water will be basic, and near the negative terminal it will be acidic. When current is stopped, equilibrium quickly will be reestablished, as the charged ions repel their similarly-charged neighbors.

In the case of AC current, there may be no non-reversible chemical changes at the electrodes, just a mess of oddly-charged ions which revert to neutral water, or there might be evolution of hydrogen and oxygen (and loss of water).

Salt raises some of the rates, and adds to the possible reactions, but is not essential: the ionizing solvent, water, has its own conductivity.

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  • $\begingroup$ True, but note - the conductivity of "deionized water" is rather small (in fact, conductivity of pure water is a measure of how pure it is). The question is about the way in which impurity ions in the liquid (which are in finite supply) would be "used up" in a chemical reaction at the electrodes. $\endgroup$ – Floris Apr 13 '17 at 12:07
  • $\begingroup$ Thank you so much for the explanation :) This helps me a lot. $\endgroup$ – Vee K. Apr 14 '17 at 12:02
  • $\begingroup$ The heating of water in a microwave oven is associated with electric currents, but NO r reactions are expected. It's just all salt water, all the time, until it boils away. That's because there's not enough energy density to push a chemical reaction, and no electrode surface that can act as catalyst. $\endgroup$ – Whit3rd Apr 15 '17 at 0:40
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Theoretically, yes.

At one point of time, all ions will be discharge (even spectator ions, if any, theoretically, will be discharged), after which the solution will lose conductivity.

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  • $\begingroup$ But practically? As in, would I be able to prove this in a lab? $\endgroup$ – Vee K. Apr 14 '17 at 0:38
  • $\begingroup$ See, I haven't tried out electrolysis in the lab for so long. You can try at your house using a combination of dc cells and salt water. $\endgroup$ – Wrichik Basu Apr 14 '17 at 4:29
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Yes, that is exaclty what happens.

Of course, it would take a lot of time to discharge a very big countainer, but the fact that in any container the solution loses conductivity as all ions have adhered to the electrodes is what makes galvanic cells (a.k.a. the basis of the electric battery) not work forever.

With a bit of knowledge on redox reactions you can even calculate how much time it takes for the saline water to lose all its conductivity, but perhaps that would be a question more appropiate for the chemistry stack exchange.

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    $\begingroup$ Thank you for the comment :) I will check on chemistry stack exchange too. $\endgroup$ – Vee K. Apr 14 '17 at 12:02

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