Process in which electric current passed through a substance causes a chemical change, usually the gaining or losing of electron s (see oxidation-reduction ).
It is carried out in an electrolytic cell consisting of separated positive and negative electrode s (anode and cathode, respectively) immersed in an electrolyte solution containing ion s or in a molten ionic compound. Electric current enters through the cathode ; positively charged cation s travel to it and combine with electrons. Negatively charged anion s give up electrons at the anode . Both thus become neutral molecules. Electrolysis is used extensively in metallurgy to extract or purify metal s from ore s or compounds and to deposit them from solution ( electroplating ). Electrolysis of molten sodium chloride yields metallic sodium and chlorine gas; that of a strong solution of sodium chloride in water (brine) yields hydrogen gas, chlorine gas, and sodium hydroxide (in solution); and that of water (with a low concentration of dissolved sodium chloride or other electrolyte) yields hydrogen and oxygen .