# EMF measured while verification of Nernst equation keeps on increasing

I was doing this experiment to verify Nernst equation in my school's lab. I had two beakers one with $\ce{ZnSO4}$ and the other with $\ce{CuSO4}$ both having a concentration of $1~\mathrm{M}$. I had a saltbridge having $4~\%$ Agar in $1~\mathrm{M}\ \ce{KCl}$. The temperature was $21.3\ \mathrm{^\circ C}$ Now the problem was that when I connected a multimeter across the electrodes it showed an EMF of $0.8\ \mathrm{V}$ initially and it went on increasing to $1.001~\mathrm{V}$. The increase was rapid initially and became slower and slower. The EMF still kept on increasing but with a very slow pace.

By what I have studied the EMF I get initially should be the maximum one and then go on decreasing as the equilibrium is attained.

So why was the EMF in my experiment increasing? Is it because I had not used wool at the ends of the salt bridge? But the Agar was already a thick gel and was not flowing out of the U-tube.

I asked my teacher and she said that there might be some problem with the multimeter. Does any one of you know the reason for the increasing EMF?

• Hi and welcome to chemistry.stackexchange.com. Thanks for already taking the tour =). I edited your post amoung others to include MathJax for maths and chemistry formatting. For more information on how to do so yourself, check out the help center, this meta-post or this one. Nice first question, btw! – Jan Dec 20 '15 at 13:15
• Do you know the materials for which the electrodes are made? – Orr22 Dec 20 '15 at 15:55
• Comment #1 re: "By what I have studied the EMF I get initially should be the maximum one and then go on decreasing as the equilibrium is attained. " // Not so much "equilibrium" but "steady state." A drop in potential would indicate some sort of polarization at the electrodes. Comment #2 - Based on #1, there is a difference between the "cell potential" and the "working voltage" as a "lot" of current is flowing through the cell. – MaxW Dec 20 '15 at 16:03
• Comment # 3 - I'd expect the multimeter to have a high input impedance and hence that little current would flow in the system. – MaxW Dec 20 '15 at 16:17
• My guess - I'd guess that the observation is due to the salt bridge. I'm thinking that it would act like a capacitor in the system. So it takes some current flow through it to reach equilibrium. // Need someone with real knowledge of salt bridges to comment on this aspect. – MaxW Dec 20 '15 at 16:23