Electrochemistry II: Electrolysis

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Electrochemistry II Electrolysis

• Experiment 33

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Electrolysis

• Electrolysis is the use of an electric current to
  make a non-spontaneous chemical reaction proceed.
• The anode is the positive electrode where
  oxidation occurs. (LEO)
• The cathode is the negative electrode where
  reduction occurs. (GER)

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The Electrolytic Cell

• An electrolytic cell converts electrical energy
  to chemical energy when an electric current
  passes through it.
• Note this is the opposite from a galvanic cell
  or voltaic cell which converted chemical energy
  to electrical energy.

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Electrolysis of Water

• The overall reaction for the electrolysis of
  water is 2H2O(l) ? O2(g) 2H2(g)
• The half-reactions are as follows
• At the anode
• 2H2O(l) ? O2(g) 4H(aq) 4e-
• At the cathode
• 4e- 4H2O(l) ?2H2(g) 4OH - (aq)
• Note the for every 2 moles of water you get 1
  mole of oxygen gas and 2 moles of hydrogen gas.

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Electrolysis of Potassium Iodide Solution

• Now you will electrolyze a solution of potassium
  iodide.
• There are 2 possible half-reactions for both
  oxidation and reduction.
• Possible oxidation half-reactions
• 2H2O(l) ? O2 (g) 4H(aq) 4e -
• 2I-(aq) ? I2(s) 2e-
• Possible reduction half-reactions
• 2H2O(l) 2e- ? H2 (g) 2OH- (aq)
• K(aq) e- ? K(s)

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Observations

• By using pH indicator you can detect the presence
  of H. If H is present, then oxidation of water
  occurred at the anode.
• If Iodine is present the solution will be brown
  and oxidation of the iodine ion occurred.
• By using pH indicator you can detect the presence
  of OH-. If you see a color change, then OH- is
  present and reduction of water occurred at the
  cathode.
• If potassium metal is plated onto the surface of
  the electrode, then reduction of the potassium
  ion occurred.

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Procedure Notes

• We will only do choice II for this experiment.
• Collect all iodine solutions.
• You will also perform the experiments on the
  handout.
• Collect all nickel plating solutions.