Electrolytes commonly exist as solutions of acids, bases or salts. In simple terms, the electrolyte is a material that dissolves in water to give a solution that conducts an electric current. Furthermore, some gases may act as electrolytes under conditions of high temperature or low pressure. Electrolyte solutions can also result from the dissolution of some biological (e.g. DNA, polypeptides) and synthetic polymers (e.g. polystyrene sulfonate), termed polyelectrolytes, which contain multiple charged moieties.
Electrolyte solutions are normally formed when a salt is placed into a solvent such as water and the individual components dissociate due to the thermodynamic interactions between solvent and solute molecules, in a process called solvation. For example, when table salt, NaCl, is placed in water, the following occurs: NaCl(s) Na+ + Cl- It is also possible for substances to react with water when they are added to it, producing ions, e.g. carbon dioxide gas dissolves in water to produce a solution which contains hydrogen ions and bicarbonate ions.
Polyelectrolytes are polymers that develop substantial charge when dissolved or swollen in a highly polar solvent medium such as water. The attendant electrostatic interactions - within a single polyelectrolyte, between polyelectrolytes, or with molecules/surfaces - produce physical properties much different than those for neutral polymers. Most polyelectrolyte solution and gel properties vary sharply with addition of simple electrolytes, which screen electrostatic interactions according to concentration.
An electrolyte in a solution may be described as concentrated if it has a high concentration of ions, or dilute if it has a low concentration. If a high proportion of the solute dissociates to form free ions, the electrolyte is strong; if most of the solute does not dissociate, the electrolyte is weak. The properties of electrolytes may be exploited using electrolysis to extract constituent elements and compounds contained within the solution.
Polyelectrolyte type chemicals generally form weak electrolytes, especially the long-chain polymers with a good deal of branched architecture within their repeating conformation. Many polyelectrolytes are not fully charged in solution at slightly alkaline to slightly acidic pH values, and their fractional charge can be modified by changing solution pH. Thus, the physical properties of polyelectrolyte solutions are strongly affected by pH and this affects their degree of charging that releases counter-ions as well as charges the polymer backbone chemical. Not only does this affect electrical conductivity of a solution but gives polyelectrolyte chemicals a variety of uses over a wide range of pH values.