Required practical 8: Measuring EMF of a cell

Question 1

First part of practical is to set up an electrochemical cell of zinc and copper

Why do you sand them down with emery paper first

Answer 1

To remove the oxide layer off the metal

Question 2

What is the method of making an electrochemical cell of zinc and copper

Answer 2

. Sand them both down with emery paper
. Wipe them down with cotton wool soaked in acetone/propanone
. Place copper into a beaker with 50cm^3 CuSO4 solution
. Place zinc into beaker with 50cm^3 of ZnSO4
So now these are both the half cell

. To make the salt bridge, plug one end of a plastic u tube with cotton wool then fill it up with NaCl and then plug the other end
Or…
Soak a piece of filter paper in potassium nitrate (KNO3).

.So join the two beakers with a U tube so the two plugged ends are in each beakers solution

.Connect the half cells with wires, crocodile clips and a voltmeter to make a circuit
Then the reading that the voltmeter gives is the emf of the cell

Question 3

What is the purpose of a salt bridge

Answer 3

It allows the ions to flow between the two electrodes to complete the circuit

Salt bridges must be inert so don’t react with the electroyte
Salt bridges must conduct electricity

Question 4

The second part of the experiment is comparing the electrode potentials of different metals

Answer 4

. Get a piece of copper, sand it down with emery paper
. Use crocodile clips and a wire to connect it to the positive terminal of the voltmeter
. Cut a piece of filter paper that is the same area as the copper, and moisten it with sodium chloride NaCl solution
. Place it on top of the metal
. Connect a second lead to the voltmeter and clip it with crocodile clip onto the other metal
. Hold the metal above the filter paper and
record voltage reading which can be positive or negative
. Repeat with different metals and compare the electrode potentials