When aq. solutions of an acid and base are mixed then

The reaction between acid and base is known as neutralisation reaction. According to Arrhenius theory of acid and base, in which a water solution of acid is mixed with a water solution of base to form a salt and water. This reaction is complete only if the resulting solution has neither acidic nor basic properties. Such a solution is called a neutral solution. Complete neutralization can take place when a strong acid, such as hydrochloric acid, HCl, is mixed with a strong base, such as sodium hydroxide, NaOH. Strong acids and strong bases completely break up, or dissociate, into their constituent ions when they dissolve in water. In the case of hydrochloric acid, hydrogen ions, H⁺, and chloride ions, Cl⁻, are formed. In the case of sodium hydroxide, sodium ions, Na⁺, and hydroxide ions, OH⁻, are formed. The hydrogen and hydroxide ions readily unite to form water. If the number of hydrogen ions in the hydrochloric acid solution is equal to the number of hydroxide ions in the sodium hydroxide solution, complete neutralization occurs when the two solutions are mixed. The resulting solution contains sodium ions and chloride ions that unite when the water evaporates to form sodium chloride.