Acids and Bases

The word 'acid' comes from the Latin acidus, meaning sour, and describes substances long recognised by their sour taste, their reaction with active metals such as zinc to liberate hydrogen gas, and their reddening of blue litmus; a base, by contrast, tastes bitter and turns red litmus blue. These classical taste-and-litmus descriptions are far too limited to explain the full range of acid-base behaviour seen in chemistry, so this unit builds up three increasingly general acid-base theories -- proposed in turn by Arrhenius, by L …