An electrolytic cell was made, below is a brief description how: Connect the cop

Question

An electrolytic cell was made, below is a brief description how: Connect the copper strip to the negative terminal of a battery and place it in a small beaker containing 2 to 3 cm of CuSO_4 solution. The clips must not contact the solution. Connect one of the other metal strips to the positive battery terminal and place it in the CuSO_4 solution, being careful that the electrodes do not touch one another. Over a 5 min period, carefully observe the solution and electrodes for evidence of plating or any other reaction.* Record your observations. Freshly clean the copper strip and replace the positive terminal with the remaining metal strip. Again observe the cell for about 5 min. Clean the three metal strips and repeat the above procedure, but with copper connected to the positive battery terminal.Observations: Copper Strip attached to negative terminal with aluminum strip attached to positive terminal: No visible reaction. Copper Strip attached to negative terminal with nickel strip attached to positive terminal: Nickel produced gas bubbles, copper looks like it had a texture change and has a pinkish hue. Copper strip attached to positive terminal with aluminum strip attached to negative terminal: Alumink^pink, copper turned a dark yellow/black. Copper Strip attached to positive terminal with nickel strip attached to negative terminal: Nickel changed to a pinkish colour and the copper developed a darker shade. For each cell that was made (total of 4), write half reactions that are consistent with the observations and write the overall cell reaction.

Explanation / Answer

Copper strip attached to negative terminal (cathode) with aluminum strip attached to positive terminal (anode):
No visible reaction.
Half reaction
3Cu + 3e- --> 3Cu- (this does not occur do to oxyde/reduction characteristics of the element)
Al --> Al3+ +3e-
Overall cell reaction:
3Cu + Al --> 3Cu- + Al3+ (this reaction does not happened)

Copper strip attached to negative terminal (cathode) with nickel strip attached to positive terminal (anode):
Nickel produced gas bubbles, copper looks like it had a texture change and has a pinkish hue:
Half reaction:
2Cu2+ + 4e- --> 2Cu(s)
2H2O --> 4H+ + O2 + 4e- (oxidation at anode)
Overall cell reaction:
2Cu2+ + 2H2O --> 4H+ + O2

Copper strip attached to positive terminal (anode) with aluminum strip attached to negative terminal (cathode):
Aluminum turned pink (actually are deposits of copper on its surface), copper turned dark yellow/black.
Cu2+ + 2e- --> Cu(s)
Cu(s) --> Cu2+ + 2e-
No overall cell reaction (concentration cell)

Copper strip attached to positive terminal (anode) with nickel strip attached to negative terminal (cathode):
Nickel changed to a pinkish colour (actually are deposits of copper on its surface) and the copper developed a darker shade.
Cu2+ + 2e- --> Cu(s)
Cu(s) --> Cu2+ + 2e-
No overall cell reaction (concentration cell)

For further information, check out the standard electrode potential for the different strips and the applied voltage.

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