electrolysis of CuSO4

• Electrolysis w Passive Electrodes

  Method: (Graphite electrodes)

  1. Pour CuSO4 solution into beaker
  2. Put two graphite rods in (1 to the -ve terminal of a DC supply, other to +ve
  3. fill two test tubes w solution n position 1 over each electrode
  4. Turn on power supply, observe what happens at each electrode
  5. Test gas produced (glowing splint / burning splint)
  6. Record observations n results

  • Analysis of results: Record observations at each electrode, inc. results of gas tests
  • Conclusion: Cu metal is formed at the negative electrode and oxygen gas is formed at the positive electrode

  
• Electrolysis w Active Electrodes (copper electrodes):

  • Cu metal frm Cu anode oxidized -> copper ions in solution
  • They migrate to cathode, reduced -> solid copper metal on cathode
  • so no of Cu2+ in solution = same thru the process = no significant change in intensity of blue colour of solution
  • However when using carbon (graphite) electrodes, O2 gas produced @ anode (oxidation of water molecules) which may react w carbon electrode / escape into the air, potentially leading to changes in the appearance of the solution
• label

  A) inert

  B) reactivity

  C) 4OH-

  D) 2H2O

  E) O2

  F) 4e-

  
• label

  A) oxidise

  B) Cu

  C) Cu

  D) Cu2+

  E) 2e-

  
• label

  A) ore

  B) cathode

  C) pure

  
• to clean the electrodes - wash with distilled water and dip in acetone and let the liquid evaporate
• Conclusion:

  • The cathode increases in mass while the anode decreases
  • This occurs as copper atoms are oxidised at the anode and form ions while copper ions are reduced at the cathode, forming copper atoms
  • The gain in mass by the negative electrode is the same as the loss in mass by the positive electrode
  • Therefore the copper deposited on the negative electrode must be the same copper ions that are lost from the positive electrode
  • That implies that the concentration of the Cu ions in the solution remains constant
• Copper(II) sulphate solution is corrosive
• if u dont understand then use this vid: https://www.onlinemathlearning.com/electrolysis-copper-sulphate.html
• Copper refining

  • pure & impure Cu electrodes
  • Electrolysis cn purify metals by separating impurities
  • impure metal always anode eg impure copper
  • cathode = pure copper
  • electrolyte: aq of soluble salt of pure metal eg CuSO4
  • Cu atoms @ anode lose electrons, go into solution as ions: Cu ⟶ Cu2+ + 2e-
  • anode becomes thinner due to loss of atoms & impurities fall out as sludge
  • Cu2+ are attracted to cathode - gain electrons & form purified Cu atoms
  • cathode becomes thicker Cu2+ + 2e- ⟶ Cu
  • anode sludge contains precious metals eg silver which are found as impurities in the unrefined copper