Write down the half-reaction that takes place at the cathode
The half-reaction that takes place at the cathode depends on the specific electrochemical cell or system being considered. In general, however, common half-reactions at the cathode can involve the reduction of anionic species or the gain of electrons. Some possible examples include:
1. Reduction of hydrogen ions (H+) to hydrogen gas (H2):
2H+ + 2e- -> H2
2. Reduction of oxygen molecules (O2) to hydroxide ions (OH-):
O2 + 2H2O + 4e- -> 4OH-
3. Reduction of metal cations (M+) to metal atoms (M):
M+ + e- -> M
Remember that the direction of the electron flow and the specific half-reaction depend on the context of the electrochemical cell or system being considered.
To determine the half-reaction that takes place at the cathode, we need to know the specific electrochemical cell or reaction in question. The cathode is the electrode where reduction occurs.
For example, let's consider the electrochemical cell involving the reduction of copper(II) ions (Cu2+) to copper metal (Cu). In this case, the half-reaction at the cathode would be:
Cu2+(aq) + 2e- -> Cu(s)
This half-reaction shows the reduction of copper(II) ions (Cu2+) to copper metal (Cu) by gaining two electrons (2e-). The (aq) notation indicates that the species is in aqueous solution, while the (s) notation indicates that the species is a solid.