RP8 - Measuring the EMF of an electrochemical cell.

Question 1

Draw a diagram to show how you would set up a electrochemical half-cell

Question 2

Describe a method that can be used to determine the EMF of an Zinc and Copper Half-cell.

Answer 2

1. Clean a piece of copper and a piece of zinc using emery paper or fine grade
   sandpaper.
2. Degrease the metal pieces using some cotton wool and propanone.
3. Place the copper into a 100 cm3 beaker with about 50 cm3 of 1.0 mol dm-3 CuSO4
   solution.
4. Place the zinc into a 100 cm3 beaker with about 50 cm3 of 1.0 mol dm-3 ZnSO4 solution.
5. Lightly plug one end of a plastic U-tube with cotton wool and fill the tube with the solution of 2.0 mol dm-3 sodium chloride solution (NaCl), then plug other end.
6. Join the two beakers with U-tube so that the plugged ends are in the separate beakers.
7. Connect the Cu(s)|Cu2+ (aq) and Zn(s)|Zn2+ (aq) half-cells by connecting the metals using crocodile clips and leads. Include a voltmeter in the circuit in order to read off the voltage.

Question 3

What is the salt bridge and describe it’s role?

Answer 3

● Allow the movement of ions between electrodes and to complete the circuit.
● Must not react (inert) with the electrolyte or ions in solution and must conduct electricity.
● Platinum is often used.
● Alternatively, a strip of filter paper saturated with NaCl solution can be used instead of a U-tube.