5.1.3 Acids, bases and buffers GapFill

An acid and the ion formed when it donates a proton, or a base and the ion formed when it accepts a proton, are called a  conjugatereciprocalgeminalmutual acid–base pair. Depending on the number of protons they are capable of donating, acids can be classified as mono-, di-, or tri  oxichydricbasicacidic. The acidity of an aqueous solution can be expressed using a   pHpDpApO value. A solution where this value barely changes on the addition of small quantities of acid or base is called a  balancedbuffermoderatorsteady solution. In acid−base titrations, the same value is often plotted against the volume of acid or base that has been added to the solution in the conical flask. The volume of acid or base that has to be added to exactly neutralise the solution is called the   correspondenceequivalenceendhalf-neutralisation point. Unless a weak acid is being titrated against a weak base, or vice versa, the reaction is also monitored using  an indicatora signala beacona marker solution. The volume of added acid or base at which the indicator changes colour is known as the   equivalencehalf-neutralisationterminationend point.