SCH4C                     Lab #19 - Electrolysis
Introduction:  When an electrical current passes through a solution of an electrolyte, chemical reactions may take place at the electrodes.  These electrolytic reactions may involve the decomposition of the electrolyte.  The reaction would then be called electrolysis.  Depending on the kind of electrodes used, electrolysis of a substance can produce different results.  In this experiment you will electrolyze copper(II) sulphate using carbon electrodes and copper electrodes respectively.
Problem:   The observe the effects of different electrodes on the electrolysis of a substance.
Apparatus:   2560 mL beaker, DC power source, connecting wires, electrode holder
Materials:   acetone, 0.5 M copper(II) sulphate solution, litmus paper, 2 carbon electrodes, 2 copper electrodes.
Safety Issues:  Acetone is poisonous and flammable.  Avoid breathing it.  Keep it away from sparks and flames and avoid spills.  Copper compounds are poisonous and should not be spilled or flushed down the drain.  Dispose of any copper(II) sulphate solution into the hazardous waster containers provided.  Beware of electrical shock. 
Procedure:
1.  After reading through this procedure, design a chart to record your results.

    

Part I
2. Clean the carbon electrodes CAREFULLY, they are extremely fragile.  Determine the mass of each electrode.
3. Set up the electrolysis cell like in the diagram above using the carbon electrodes.  Dip a piece of blue litmus paper into the electrolyte and record the pH.  Adjust the voltage to 5.0 V and pass current through the solution for 20 minutes.
4. Remove the cathode (the electrode which has changed colour). rinse it with distilled water and then with acetone.  Allow it to dry and then determine its mass.  Do the same with anode.
5. Dip a piece of blue litmus paper into the electrolyte and record the pH and nay other observations.

   

Part II
6. Clean the cooper electrode with sand paper or steel wool.  Rinse with distilled water and then with acetone.
7. Identify the cathode with a marking.  Determine the mass of each electrode.  Repeat Steps 3, 4 and 5.
8. Compare the colour of the electrolyte before and after the electrolysis.  Record your observation.  Dispose of the copper solution according to WHMIS hazardous materials disposal procedures.


Calculation:     Calculate the change in mass for each of the four electrodes.
Concluding Questions
1. Which carbon electrode is more massive after the electrolysis? Explain.
2. Account for the colour change in the electrolyte in Part I.  What does the litmus test suggest?
3. Write the half cell and the over all reaction for Part I
4. Account for the mass changes of the copper electrodes.  What does this suggest about the electrolysis of copper(II) sulphate using copper electrodes?  What is the supporting evidence from the experiment?
5. Summarize the importance of the electrodes in the electrolysis of a substance.
6. What would be the difference if lead electrodes were used in Part I instead of carbon ones?  Explain.
7. How could you use electrolysis to purify the following:
a)  a bar of nickel         b) an impure gold ingot