Chemical changes Study Guide

Electrolysis is a process that uses electrical energy to drive non-spontaneous chemical reactions. It occurs in an electrolyte, which is an ionic compound either molten or dissolved in a suitable solvent, containing free-moving ions. When an external direct current is applied, two electrodes are immersed in the electrolyte: a positively charged anode and a negatively charged cathode. Positively charged ions, called cations, are attracted to the negatively charged cathode. At the cathode, cations gain electrons (reduction). Conversely, negatively charged ions, called anions, are attracted to the positively charged anode. At the anode, anions lose electrons (oxidation). This directed movement and subsequent reaction of ions constitute the mechanism by which electrolysis drives chemical change and enables the extraction of reactive metals or separation of elements from compounds.

When acids are dissolved in water, they release hydrogen ions (H⁺) into the solution. It is these hydrogen ions that are responsible for the characteristic acidic properties, such as a sour taste or reacting with metals to produce hydrogen gas. Conversely, alkalis are soluble bases that release hydroxide ions (OH⁻) when dissolved in water. These hydroxide ions are responsible for the characteristic alkaline properties, such as a slippery feel or reacting with acids in neutralisation reactions. The concentration of these ions determines the strength of the acid or alkali, and therefore its pH. Strong acids and alkalis fully dissociate in solution, releasing a high concentration of H⁺ or OH⁻ ions, respectively, while weak acids and alkalis only partially dissociate.