RP8 Measuring EMF of an Electrochemical cell

Method

• Clean a piece of copper and a piece of zinc using emery paper or fine grade sandpaper

• Degrease the metal using cotton wool and propanone if needed

• Place the copper into a 100cm3 beaker and fill with 25cm3 of 1moldm-3 of CuSO4 solution

• Place the zinc into a 100cm3 beaker and fill with 25cm3 of 1moldm-3 of ZnSO4 solution

• Connect the cells with an appropriate length of filter paper that has been soaked in saturated potassium nitrate solution (having allowed any excess to drain first)

Why would the electrode potential values for the cells set up slightly vary from the theoretical values?

• Not under standard conditions (not 298K)

• May be an oxidation layer on the metal electrodes

• High Internal Resistance - salt bridge used might not allow ions to flow freely enough, causing high internal resistance and a lower measured voltage e.g. if salt bridge is not saturated

Why were we not able to include a magnesium cell in this experiment?

• Magnesium will react with the water.

• While this is a slow reaction it still makes the data more unreliable than zinc, iron, copper

calculate the emf

• EMF = E0 of RHS - E0 of LHS