Polyprotic acid distribution

Visualize how every protonation state changes with pH for acids with one to seven dissociable protons.

For an acid with $n$ dissociable protons, the fractional composition $\alpha_j$ is the fraction present after $j$ protons have dissociated. Enter the stepwise $\mathrm{p}K_a$ values to compare all $n+1$ forms on one graph.

The fractions are calculated from the complete equilibrium distribution, so at every pH

\sum_{j=0}^{n}\alpha_j=1.

Move the composition slider across the graph to inspect the exact fraction and percentage of every species.

EQUILIBRIUM LAB

Acid distribution diagram

H_nA ⇌ … ⇌ Aⁿ⁻

Choose the number of protons and the stepwise pKa values. The graph shows the fraction (α) of the total acid present in every protonation state.

Composition at pH 7.00

At each pKa, two adjacent forms have equal fractions. All α values always sum to 1.