Electrolytes and Solubility

Electrolyte = A solute that produces ions in solution.

Electrolytic Solution = A solution that conducts electricity.

When an electrolyte dissolves in water (or another solvent) it forms an electrolytic solution. Why?

Electricity is the flow of charged species in response to the application of an electric field gradient.

Solutions can also conduct electricity, but the charge carriers are now ions.

For example pure water is a very good insulator, but if we add sodium chloride we create ions to form an electrolytic solution.

NaCl(s) + H2O(l) Na+(aq) + Cl-(aq) + H2O(l)

Therefore, NaCl is an electrolyte.

It is important to realize that a compound may dissolve in water (soluble) but not dissociate into ions. Such compounds do not form ions and thus do not produce electrolytic solutions. They are called non-electrolytes. Examples of non-electrolytes include sugar and ethanol.

Non-electrolyte = A solute that dissolves without producing ions.

Demo – conductivity of distilled H2O, sugar water & NaCl(aq)

Electrolytes can be further classified into strong and weak electrolytes.

Strong electrolyte = A solute that dissolves almost completely to ions (i.e. soluble inorganic salts, strong acids & bases).

Weak electrolyte = A solute that only partially dissolves into ions (i.e. weak acids and bases).

To illustrate the distinction between strong and weak electrolytes consider two solutions each one containing 1,000,000 molecules of solute.

Solution A Solute = HCl Strong electrolyte

Solution B Solute = HC2H3O2 Weak electrolyte

If we look at the solute species present in each solution we might find approximately the following numbers.

Solution A

Solution B

Demo – Conductivity of acetic acid and HCl.

As a final note be careful not to confuse the solubility of a substance in water with whether it is a weak, strong or non-electrolyte. For example sugar dissolves completely in water, but does not form ions so it is a non-electrolyte. On the other hand BaSO4 only dissolves very slightly in water, but the amount of salt that does dissolve completely dissociates into Ba2+ and SO42- ions, so BaSO4 is a strong electrolyte.