Answer to Question #239775 in General Chemistry for spence

Question

A copper/silver electrochemical cell is set up - Cu | Cu²⁺ Ag⁺ | Ag

Using the following values, calculate the potential difference that is expected.

Standard electrode potential of Cu | Cu²⁺ = +0.34V

Standard electrode potential of Ag⁺ | Ag = +0.80V

Explain why the measured potential difference may not be precisely that predicted

Answer 1

V = IR

= 0.34× 0.8 = 0.272volts

There are many things which cause the cell potential not to be predicted.

Anything at all which causes any internal resistance in the cell or the circuit being used to measure it will reduce the measured potential.

As well, frequently, non standard conditions may be used in a lab.

The standard cells are for 1 M solutions. They are measured at 25 degrees Celsius. Differences in these conditions will cause changes. If a reactant or product is a gas, it needs to be bubbled over a platinum (inert) electrode with a pressure of 1 atm.

Other much more significant differences also impact. Unless the electrodes are super clean, with a fresh metal surface that has no oxide layer at all, then the oxide layer will interfere with the reaction and reduce the measure potential. The salt bridge can cause interference to the easy flow of ions, and so cause internal resistance and lower the measured potential. How much will depend on a lot of factors about how it is made etc.