. Acids and bases The term ‘acid’ is derived from the latin word ‘acidus’ meaning sour. We have already learnt in earlier classes that acid tastes sour, turns blue litmus to red and reacts with metals such as zinc and produces hydrogen gas. Similarly base tastes bitter and turns red litmus to blue.
These classical concepts are not adequate to explain the complete behaviour of acids and bases. So, the scientists developed the acid – base concept based on their behaviour. Let us, learn the concept developed by scientists Arrhenius, Bronsted and Lowry and Lewis to describe the properties of acids and bases. .
. Arrhenius Concept One of the earliest theories about acids and bases was proposed by swedish chemist Svante Arrhenius. According to him, an acid is a substance that dissociates to give hydrogen ions in water. For example, HCl, H SO etc., are acids.
Their dissociation in aqueous solution is expressed as HCl(g) H (aq)+Cl (aq) H O ⇀ ↽ The H + ion in aqueous solution is highly hydrated and usually represented as H O + , the simplest hydrate of proton H(H O)