From many years, we know about acid and bases. If we look around, there are lots of examples of acid and bases, like lemon juice and vinegar taste sour where as soap and lye are bitter in taste.

So in general,  acids are the compound which has sour taste, turns litmus red and gives Hydrogen ion [H⁺], when comes in contact with water whereas bases are the compound which has bitter taste, turns litmus blue and gives Hydroxide ion [OH^-] when comes in contact with water. Based on their properties, acids and bases are classified as Arrhenius acid and base, Bronsted acid and bases and Lewis acid and bases. Arrhenius acid gives H⁺ ion and Arrhenius base gives OH^- ion in water. Bronsted acid donates proton whereas Bronsted base accepts protons. Lewis acid accepts electron pair and Lewis base donates electron pair. Acid reacts with Base to form salt and water and the reaction is called as Neutralization.

The ability of acid to react with base is based on Hydrogen ion and hydroxide ion concentration and according to that they are defined as strong acid, strong base, weak acid and weak base. Acidity and basicity of a solution is measured by pH. pH is defines as the negative logarithm (base 10) of the molar concentration of dissolved hydronium ions [H₃O⁺]. Pure water is a neutral solution having pH equal to 7.0. Solution less than pH 7.0 is called as acidic solution whereas solution less than pH 7.0 is called as alkaline solution. The solution which resists the change in pH when small quantities of acid or alkali is added to it, is called as buffers. Solution with pH less than 7.0 are acid buffer solution e.g. mixture of ethanoic acid and sodium etanoate. Solution with pH greater than 7.0 are alkaline buffer solution e.g. misture of ammonia and ammonium chloride.