RP8 - Measuring EMF of an electrochemical cell Flashcards
What is an electrochemical cell?
● Two different half-cells are connected by a salt
bridge, with their electrodes connected to a
voltmeter (measures EMF/cell potential). This
allows the flow of electrons.
● The electrical energy generated is from chemical redox reactions.
What does a half-cell consist of?
● Half-cells are usually metal/metal ion (metal
electrode in the metal ion solution) or ion/ion
● Each half cell will contain the chemical species from one half of a redox reaction (redox half equation).
What is a salt bridge?
● A salt bridge allows the transfer of ions.
● It is typically a concentrated solution of an electrolyte i.e. KNO3(aq) that doesn’t react with either half cell solution.
Why may a graphite or platinum electrode be used?
They are very unreactive- i.e. will not react with the half cell solutions and will
not affect the voltmeter readings. Usually used in ion/ion half cells.
How do you measure comparative electrode
potentials of different metals?
● 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 a table.
Why do you need to file/ sand away the outer layer of the metal?
It removes the oxide layer on the outside of the metal.
