What will happen if we do electrolysis with AC

Why electrolysis occurs only with DC not AC?

Image Source: Wikipedia.com

Today I am going to describe it with an example of electrolysis. If we take a beaker with CuSO₄ in it and place two copper rods connected with two terminals of the battery and flow electricity through it from a DC source. Then one rod will act like cathode and one like anode. The rod which is connected with the positive terminal of the battery called as anode and the rod which is connected with negative called as cathode.

When we do all these setups then electrolysis starts there.

What happens at anode in this process?

When we give DC current to the system, then at anode Cu²⁺ get out from the solid copper rod and get dissociated in the Copper sulphate solution by leaving 2 electrons in the copper solid (Anode). And due this, CuSO₄ get a positive charge in it and copper solid rod (anode) start gaining more and more electrons and becomes negative charged.

What happens at cathode in this process?

When we give DC current to the system, then at cathode Cu²⁺ from the CuSO₄ solution go towards the copper solid rod (cathode) and by gaining 2 electrons from the cathode rod turns into copper solid which is gathered at cathode. And due to these all processes copper solid gets positive charge and CuSO₄ solution gets negative charge. This leads to flow of electrons from anode to cathode in the wire which is connected to the battery and the electrolytic solution.

So, this is what which happens when we apply DC current to the system now see what happens when we apply AC current to the same system. First of all, understand what is AC current. AC stands for alternating current unlike DC this current change its direction many times in a second. In India, each house is supplied with 220 V AC current with 50Hz of frequency. But in countries like USA each house supplied with 100 V AC current with 60Hz frequency.

[1 Hz frequency means 1 oscillation per second, here 60 Hz means 60 oscillation per second]

Now, suppos that we have connected our electrolyte with 100 V AC having 60 Hz of frequency. And dipped two electrodes A and B. So, the direction of the flow of electric current is changing 60 * 2= 120 times in each second. And if we go with Faraday’s first law of electrolysis which is “The amount of deposited or evolved material is directly proportional to the applied electricity. So, the amount of deposited copper at electrode A is equal to deposited copper at electrode B. But wait, why I said copper is depositing at both electrodes. AC current is fluctuating current in which the direction of current is not determined. The direction of the current changes many times in a second. As the direction of the flow of current changes that's why anode and cathode also changes and due to which copper get deposited on the both.

Comparison of rate of electrolysis with the frequency graph of AC.

Because only for 0.83ms current flow from A to B and in next 0.83ms current flows from B to A due to which in each second the amount of deposited copper at anode and cathode reduced with same amount. Simply, we can say that in half second copper [Cu (s)] deposit at electrodes and next half second it reduced, overall there is no electrolysis is taking place.

Two copper electrode in coppersulphate solution connected with an AC source.

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