posted by Raj on .
How can I tell whether something is a weak, strong, or non-electrolyte?
I know non-electrolytes do not ionize, strong almost completely ionize and weak only partially.
But how would I be able to tell? Like, something like KOH is a strong electrolyte because it can ionize into OH^- and K^+ ions, but why is something like water a weak electrolyte, even though it can ionize into OH^- an H^+ ions.
We talk mostly about acids in water solution; therefore, the strength of an acid or base depends upon how it reacts with water. For example,
HCl(g) + H2O ==> H3O^+ + OH^-
In this case, the extra pair of electrons on the H2O molecule (remember it has two unshared pairs) attract the H^+ from HCl to form H3O^+ and that leaves the Cl^- to stand alone. Said another way, H2O is a stronger base than Cl^-; that is, the H2O molecule to H^+ bond formed is stronger than the
H-Cl bond. So whether an acid or a base is strong or weak depends upon the H-X bond strength versus the H-O-H bond strength. From a practical point, just keep a chart of ionization constants for acids and bases (Ka and Kb) handy. If the compound has a Ka or Kb it is week. If not, it is strong (or it could be insoluble in water).