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An electrolyte is any salt or ionizable molecule that, when dissolved in solution, will give that solution the ability to conduct electricity. This is because when a salt dissolves, its dissociated ions can move freely in solution, allowing a charge to flow.
Electrolyte solutions are normally formed when a salt is placed into a solvent such as water. For example, when table salt, NaCl, is placed in water, the salt (a solid) dissolves into its component ions, according to the dissociation reaction:
NaCl(s) → Na+(aq) + Cl−(aq)
It is also possible for substances to react with water to yield ions in solution. For example, carbon dioxide gas, CO2, will dissolve in water to produce a solution that contains hydrogen ions, carbonate, and hydrogen carbonate ions:
The resulting solution will conduct electricity because it contains ions. It is important to keep in mind, however, that CO2 is not an electrolyte, because CO2 itself does not dissociate into ions. Only compounds that dissociate into their component ions in solution qualify as electrolytes.
Strong and Weak Electrolytes
As mentioned above, when an ionizable solute dissociates, the resulting solution can conduct electricity. Therefore, compounds that readily form ions in solution are known as strong electrolytes. (By this reasoning, all strong acids and strong bases are strong electrolytes.)
By contrast, if a compound dissociates to a small extent, the solution will be a weak conductor of electricity; a compound that only dissociates weakly, therefore, is known as a weak electrolyte.
A strong electrolyte will completely dissociate into its component ions in solution; a weak electrolyte, on the other hand, will remain mostly undissociated in solution. An example of a weak electrolyte is acetic acid, which is also a weak acid.
Nonelectrolytes are compounds that do not ionize at all in solution. As a result, solutions containing nonelectrolytes will not conduct electricity. Typically, nonelectrolytes are primarily held together by covalent rather than ionic bonds. A common example of a nonelectrolyte is glucose, or C6H12O6. Glucose (sugar) readily dissolves in water, but because it does not dissociate into ions in solution, it is considered a nonelectrolyte; solutions containing glucose do not, therefore, conduct electricity.