Question

In electrochemistry, why is my experimental voltage value of my cell lower than the standard electrode potential? I used zinc and copper as the electrodes and connected zinc sulphate and copper(II) sulphate using a salt bridge. I got 0.85V instead of 1.10V.
I've read that maybe there might be contamination. What contamination might affect the values? Are there any other reasons I should take note of?

Thanks a lot for your help.

How did you measure the voltage? If you used a voltmeter that takes too much power to operate it the small cell can't supply the current needed to operate the meter; therefore, the voltage drops. Also, if the copper and zinc solutions are not 1 M, that will affect the voltage. Good connections are necessary, otherwise you will have a voltage drop across the resistance at the poor connection. Contamination that you mention may affect the concentration of the solutions as above (so they aren't 1 M); also, some contaminants may react with the copper or zinc electrodes themselves.

Would 1 M be 1 mol/dm3?
Thanks, Dr Bob.

Yes, 1 molar = 1 mol/L = 1 mol/1000 cc = 1 mol/cubic decimeter