Question

So we're doing oxidation-reduction reactions and batteries and voltages.

We did a lab where we would take two metals, put it in a mixture (bleach/water/vinegar/salt) and used a voltmeter to see the DC voltage.

Now we're supposed to 'calculate the potential difference' for some of the combinations, given this info:

"STANDARD REDUCTION POTENTIALS IN AQUEOUS SOLUTION AT25°C" (google it for the link since jishka won't let me post it)

so I'll just ask for one example: zinc and aluminum. the DC voltage I got was 0.213 if it matters. how do I do it? thanks :)

also if someone knows how to find which copper charge i'm supposed to use since there are three different ones..

Answer 1

First, the usual one to use for Cu is
Cu ==> Cu^2+ + 2e

The potential for the Al/Zn couple, using standard reduction potential (but from my text which is several years old--it may not match your data).
Al + 3e = Al(aq) Eo = about -1.66 red pot
Zn + 2e ==> Zn(aq) Eo = -0.763
Reverse the more negative value and add to the other one; ie.,
Al ==> Al^3+ + 3e 1.66
Zn^2+ + 2e ==> Zn -0.763
Sum = 1.66 + (-0.763) = 0.897 or close to that is what you should have obtained in the lab IF you used the right measuring equipment.

Answer 2

And if the solutions were 1M.