By Donny Quinn, Updated Mar 24, 2022

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Strong acids and bases fully dissociate in aqueous solution, meaning every acidic molecule donates a proton or every alkaline molecule releases a hydroxide ion. Weak acids, such as hydrofluoric acid, and weak bases, such as ammonia, only partially dissociate. Calculating the percentage of dissociation—the fraction of molecules that ionize—provides insight into their behavior.

Step 1: Determine the Quantity of Dissociated Species

In many problems this value is supplied directly. In more advanced contexts you may need to derive it from equilibrium expressions or experimental data.

Step 2: Divide by the Initial Concentration

Take the moles‑per‑liter of dissociated species and divide by the initial moles‑per‑liter of the acid or base. The initial concentration is usually provided on the reagent label or in the problem statement.

Step 3: Convert to a Percentage

Multiply the result by 100 to express the degree of ionization as a percent.

TL;DR

When the direct dissociation value isn’t given, you’ll need to work through equilibrium expressions—often using the acid dissociation constant (K_a)—to calculate the percent dissociation.

Understanding this calculation helps chemists predict how weak acids and bases behave in solution.