Strong versus Weak Acids and Bases

A crucial distinction in acid-base chemistry is between strength and concentration, two ideas that students often confuse. Concentration measures how many moles of acid or base are dissolved per unit volume of solution. Strength measures the extent to which the acid or base ionizes in water. A strong acid is fully (or almost fully) ionized in aqueous solution, meaning nearly every molecule donates its proton. A weak acid is only partially ionized, so at equilibrium the solution contains mostly intact molecules and only a small proportion of ions. It is perfectly possible to have a concentrated weak acid or a dilute strong acid; the two properties are independent.

Common strong acids include hydrochloric acid ($HCl$), nitric acid ($HNO_3$), and sulfuric acid ($H_2SO_4$). Their ionization is