Chemical changes Study Guide

Electrolysis is a process that uses electrical energy to drive non-spontaneous chemical reactions. When a binary, ionic compound is in a molten state, its ions are free to move. During electrolysis, these mobile ions are attracted to oppositely charged electrodes. At the negative electrode (cathode), positively charged metal ions (cations) gain electrons and are reduced to form the neutral metal element. At the positive electrode (anode), negatively charged non-metal ions (anions) lose electrons and are oxidised to form the neutral non-metal element. For example, in the electrolysis of molten sodium chloride, sodium ions (Na+) are attracted to the cathode and form sodium metal, while chloride ions (Cl-) are attracted to the anode and form chlorine gas.

Insoluble salts are typically prepared by a precipitation reaction. This method involves mixing solutions of two soluble salts, where the cation from one solution combines with the anion from the other to form an insoluble product. This product, known as the precipitate, then separates from the solution. For example, to make silver chloride, a soluble silver salt (like silver nitrate) is mixed with a soluble chloride salt (like sodium chloride). The silver ions react with the chloride ions to form solid silver chloride, which is insoluble. Once the precipitate has formed, it needs to be separated from the soluble reactants and purifie. This usually involves filtration, washing the precipitate to remove impurities, and then drying it to obtain a pure, dry sample.