what is the principal difference between a strong and weak acid?
An example of a strong acid is hydrochloric acid. A strong acid has a pH of 1. hydrogen chloride (in water) hydrogen ion + chloride ion HCl(aq) H+(aq) + Cl-(aq). All of the hydrogen chloride molecules become hydrogen ions and chloride ions when they are dissolved in water (see examples of other strong acids).
An example of a weak acid is ethanoic acid. A weak acid has a pH of 3 to 5. ethanoic acid (in water) hydrogen ion + ethanoic ion CH3CO2H(aq) H+(aq) + CH3CO2-(aq) Some of the ethanoic acid molecules become ions in water but most of them stay as molecules. The reaction is reversible (shown by the arrow).