A strong acid is a substance that completely ionizes (breaks down) into its ions in water. This means it donates all of its hydrogen ions (H+) when dissolved in water.
Related terms
Bronsted-Lowry Acid: An acid according to Bronsted-Lowry theory is any substance that can donate a proton (H+).
Hydronium Ion (H3O+): The ion formed from water gaining a hydrogen ion (H+) from an acid.
pH Scale: A measure of how acidic or basic a solution is, based on its concentration of hydronium ions.