Dissociation is a very important chemical process. When molecules dissociate, they break up to smaller pieces, which leave or take extra electrons from the other pieces. These are called ions. The pieces can reassemble themselves back to the original molecule, because the electric charges attract the pieces to each other. The familiar properties of salty, acidic, basic and alkaline solutions are caused by the dissociation. Salts dissociate to their ions, acids dissociate to hydrogen ions, alkali dissociate to hydroxide ions and non-alkali bases make water dissociate to hydroxide ions by absorbing hydrogen ions.
Dissolution of salts is a dissociation process. Polar solvents (e.g. water) can break the crystalline structure of an ionic crystal (e.g. table salt) and dissolve the substance. The crystal is dissociated into ions. That is, there are no molecules of sodium chloride floating in the solution, but individual sodium and chloride ions. When the water is boiled away, the salt reassembles itself back to the crystals.
NaCl (s) -> Na+(aq) + Cl-(aq)
The taste and the smell of a dissociating substance is not the taste of the crystal, but the taste of the ions it dissociates into. Table salt tastes of sodium ions and chloride, salmiakki tastes of ammonium and chloride, citric acid tastes of citrate and hydrogen ions, etc.
Ionic salts and strong acids dissociate completely, but some substances dissociate only partially, forming a dynamic equilibrium between the whole and dissociated states. When one breaks up, another reassembles, so that the total ratio between them is constant. This is an important type of chemical equilibrium, which includes weak acids, weak bases and acidic or basic salts.