In electrolysis, if no halogens are present in the anode environment, oxidation at the anode may produce which gas?

In electrolysis, if no halogens are present in the anode environment, oxidation at the anode may produce which gas?

• A. Oxygen gas
• B. Hydrogen gas
• C. Chlorine gas
• D. Nitrogen gas

Answer: (A)

At the anode, oxidation occurs and the species that gets oxidized is the one available and easiest to oxidize among those in solution. If no halide ions are present, water is the species that can be oxidized, so it loses electrons to form oxygen gas: 2 H2O → O2 + 4 H+ + 4 e-. In basic conditions this becomes 4 OH− → O2 + 2 H2O + 4 e−. Halogens would be formed instead only if halide ions were present, since they are oxidized more readily than water. Hydrogen gas, meanwhile, is produced at the cathode by reduction of water, not at the anode.

At the anode, oxidation occurs and the species that gets oxidized is the one available and easiest to oxidize among those in solution. If no halide ions are present, water is the species that can be oxidized, so it loses electrons to form oxygen gas: 2 H2O → O2 + 4 H+ + 4 e-. In basic conditions this becomes 4 OH− → O2 + 2 H2O + 4 e−. Halogens would be formed instead only if halide ions were present, since they are oxidized more readily than water. Hydrogen gas, meanwhile, is produced at the cathode by reduction of water, not at the anode.