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How to Determine Anode & Cathode Half-Reactions

Batteries are an indispensable component of our modern mobile world. Without batteries, we'd all need long extension cords attached to our cell phones, which would be dangerous and, frankly, ridiculous. Batteries generate electrical energy through controlled chemical reactions, of which there are two: an oxidation reaction at the anode produces electrons, and a reduction reaction at the cathode absorbs them.

Instructions

- 1
  Identify which two types of metal make up your cathode and your anode. Different types of battery use different types of metals and solutions containing ions of those metals. One simple type of battery uses a copper (Cu) cathode and a zinc (Zn)anode.
- 2
  Identify what aqueous solutions containing ions of these metals are used in your battery. The copper-zinc battery typically uses solutions of CuSO4 and ZnSO4.
- 3
  Determine the valence of your anions in solution, and use this to determine the valence of your cations. For SO4, it's -2. So the CuSO4 solution has SO4 ions with a charge of -2 associated with Cu ions that must have a +2 valence in order to balance. The ZnSO4 has SO4 ions with a -2 charge associated with +2 charged Zn ions.
- 4
  Write the half equation at the anode. This is the reaction that produces electrons. The metallic zinc has to lose those electrons, going into solution as Zn ions with a +2 charge. The half reaction therefore is: Zn(s) ' Zn+2(aq) + 2 e-. In these equations "aq" indicates that the ions are in an aqueous solution and "s" indicates that the metal is in a solid form. "e-" represents electrons.
- 5
  Write the half equation at the cathode. The cathode absorbs electrons, bringing positively charged copper ions out of solution by balancing them with the incoming electrons. The half-reaction therefore is Cu+2(aq) + 2 e- ' Cu(s).

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