RP 08 Measuring EMF of an electrochemical cell

• What is an electrochemical cell?

  • Two different half-cells are connected by a salt bridge, with their electrodes connected to a voltmeter (measures EMF). This allows for 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 (ions that are the same elements 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)
• What is a salt bridge?

  • Allows the transfer of ions
  • It is typically a concentrated solution of an electrolyte that doesn't react with either half cell solution
• Why may a graphite or platinum electrode be used?

  They are very unreactive and will not react with the half cell solutions and will not affect the voltmeter readings. Usually 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 voltmeter to another piece of metal
  • Gold 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