I can’t inderstand a Chemistry experiment. There is a half cell with Copper sulfate pentahydrate and two electrodes of copper and zinc. How can voltage pass?

Question

We did the experiment without a battery and we checked the voltage connecting the two electrodes with a voltmeter and worked. I can’t figure out how can it work without a battery supply because it is only half cell and both electrodes are in the same cell. Please help.

Answer 1

The copper and the zinc will undergo oxidation/reduction where reduction will take place at the Cu electrode and oxidation at the Zn electrode. This is based on the fact that reduction potential for Cu²⁺ is greater than that of Zn²⁺.  Thus, 

Cu²⁺ + 2e- ==> Cu(s) at the Cu electrode and

Zn(s) ==> Zn²⁺ + 2e- at the Zn electrode

Without a salt bridge, and with both electrodes in the same bath, the current will not last long because there will be no neutralization of charge build up.  So, while a voltage will pass, it will be of very short duration.  Also, I wouldn't agree that you have only a half cell.  You still have 2 half cells, but they aren't separated.