Acids, Bases, Arrhenius

Learning Goals

You will learn the definitions of acid and base according to the model of Arrhenius.

Synopsis

The word acid comes from a word that means sour. The word alkali comes from a word that describes the remains left after burning certain plants and these remains feel rather slippery when wet. The word salt probably originates from a word meaning sea salt. Later a salt was defined as a product of the reaction of an acid with a base. The definition of acid according to the Swedish chemist Arrhenius is any compound that can release a hydrogen atom upon ionic dissociation of the compound in water solution. Arrhenius defined a base as a substance that can produce a hydroxide ion in a water solution. NaOH is obviously an Arrhenius base for it dissociates in water to Na⁺ and OH^-. However, ammonia is also a base, for in water it forms the hydroxide ion. The source of the hydroxide ion does not have to be the "base." The reaction of an acid and a base will produce a salt. The Arrhenius definition limits the concept of acid and base to water solutions. We will study other models that are not so limited.

Review Question

Show by a balanced chemical equation how each of the following is classified as a base by the Arrhenius model: Ba(OH)₂, NH₃, and H₂O.
Show by a balanced chemical equation how each of the following is classified as an acid by the Arrhenius model: HCl, CH₃COH, and H₂O.