2H2O+2e−→2OH−+H22H_{2}O + 2e^{-} \rightarrow 2OH^{-} + H_{2}2H2O+2e−→2OH−+H2 and hydrogen gas will bubble up. The anode reaction is:2NaCl→2Na++Cl2+2e−2NaCl \rightarrow 2 Na^{+} + Cl_2 + 2e^{-}2NaCl→2Na++Cl2+2e− and chlorine gas will be liberated. The positively-charged sodium ions Na+ will react toward the cathode, neutralizing the negative charge of OH− there; the negatively-charged hydroxide ions OH− will react toward the anode, neutralizing the positive charge of Na+ there. Without the ions from the electrolyte, the charges around the electrode slow continued electron flow; diffusion of H+ and OH− through water to the other electrode takes longer than movement of the much more prevalent salt ions. In other systems, the electrode reactions can involve electrode metal as well as electrolyte ions. In batteries for example, two materials with different electron affinities are used as electrodes: outside the battery, electrons flow from one electrode to the other; inside, the circuit is closed by the electrolyte's ions. Here, the electrode reactions convert chemical energy to electrical energy. Oxidation of ions or neutral molecules occurs at the anode, and the reduction of ions or neutral molecules occurs at the cathode. Two mnemonics for remembering that reduction happens at the cathode and oxidation at the anode are: "Red Cat" (reduction - cathode) and "An Ox" (anode - oxidation). The mnemonic "LeO said GeR" is useful for remembering "lose an electron in oxidation" and "gain an electron in reduction." It is possible to oxidize ferrous ions to ferric ions at the anode. For example:Fe2+(aq)→Fe3+(aq)+e−Fe^{2+}(aq) \rightarrow Fe^{3+} (aq) + e^{-}Fe2+(aq)→Fe3+(aq)+e− +2e−+2H+→+ 2 e^{-} + 2 H^{+} \rightarrow+2e−+2H+→ HydroquinoneHydroquinone is a reductant or electron donor and organic molecule. Para-benzoquinoneP-benzoquinone is an oxidant or electron acceptor.In the last example, H+ ions (hydrogen ions) also take part in the reaction, and are provided by an acid in the solution or by the solvent itself (water, methanol, etc.). Electrolysis reactions involving H+ ions are fairly common in acidic solutions, while reactions involving OH- (hydroxide ions) are common in alkaline water solutions. The oxidized or reduced substances can also be the solvent (usually water) or electrodes. It is possible to have electrolysis involving gases. In order to determine which species in solution will be oxidized and which will be reduced, the standard electrode potential of each species may be obtained from a table of standard reduction potentials, a small sampling of which is shown here:Eox0(V)E_{ox}^0 (V)Eox0(V) Ered0(V)E_{red}^0 (V)Ered0(V) = +1.36 V in the table. Recall that a more positive potential always means that that reaction will be favored; this will have consequences concerning redox reactions.Show Sources CC licensed content, Shared previously |