Chemistry - Electrochemistry (Electrolysis and electroplating)

Electrolysis is the breakdown of an ionic compound, molten or in aqueous solution, by the passage of electricity. The substance being decomposed is called the electrolyte.

The Anode is the positive electrode where oxidation occurs (loss of electrons). The Cathode is the negative electrode where reduction occurs (gain of electrons). Remember the mnemonic OIL RIG (Oxidation Is Loss, Reduction Is Gain).

In the electrolysis of molten salts, such as molten $PbBr_2$, the metal is produced at the cathode ($Pb^{2+} + 2e^- \rightarrow Pb$) and the non-metal at the anode ($2Br^- \rightarrow Br_2 + 2e^-$).

In aqueous solutions, water provides $H^+$ and $OH^-$ ions. At the cathode, $H_2$ gas is produced if the metal in the salt is more reactive than hydrogen (e.g., $Na$, $K$, $Mg$). If the metal is less reactive (e.g., $Cu$, $Ag$), the metal is deposited.

At the anode in aqueous solutions, oxygen gas ($O_2$) is produced from $OH^-$ ions unless the solution contains a high concentration of halide ions ($Cl^-$, $Br^-$, $I^-$), in which case the halogen is produced.

Electroplating is the process of coating a metal object with a thin layer of another metal using electrolysis. The object to be plated is made the cathode, and the plating metal is made the anode. The electrolyte must be a solution of a soluble salt of the plating metal.

In the refining of Copper, an impure copper anode dissolves into the electrolyte, and pure copper atoms are deposited onto the cathode: $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$.