Rp 08- Measuring EMF Of An Electrochemical Cell

Question 1

What is an electrochemical cell?

Answer 1

Two different half-cells are connected by a salt bridge, with their electrodes connected to a voltmeter. This allows flow of electrons.
The electrical energy generated is from chemical redox reactions.

Question 2

What does a half cell consist of?

Answer 2

Half-cells are usually metal/metal ion (metal electrode in metal ion solution) or ion/ion (ions that are the same element but with different oxidation states, in solution)
Each half cell will contain the chemical species from one half of a redox reaction (redox half equation)

Question 3

What is a salt bridge?

Answer 3

• a salt bridge allows the transfer of ions
• is typical a concentrated solution of an electrolyte I.e. KNO3 (aq) that doesn’t’t react with either half cell solution

Question 4

Why may a graphite or platinum electrode be used?

Answer 4

They are very unreactive. They won’t react with half cell solutions and will not affect voltmeter readings. Usually used in ion/ion half cells.

Question 5

How do you measure comparative electrode potentials if different metals?

Answer 5

• file a piece of copper using emery paper and connect it to the positive voltmeter terminal
• cut a piece of filter paper, saturate with KNO3 solution and place on top of the copper
• connect the voltmeter to another piece of metal
• hold the metal against the filter paper and record the voltmeter value
• repeat with different metals and record the results in the table.

Question 6

Why do you need to file/sand away the outer layer of the metal?

Answer 6

It removes the oxide layer on the outside of the metal.