The acid dissociation constant measures the strength of a weak acid. Larger Ka means stronger acid (more dissociation).

pKa = -log10(Ka). Lower pKa means stronger acid. It is more convenient for comparing acids.

Do strong acids have Ka values?

Strong acids fully dissociate, so their Ka is very large (effectively infinite). Ka is mainly used for weak acids.

Free Ka Calculator

Calculate the acid dissociation constant (Ka) from equilibrium concentrations of a weak acid.

Save

[H+] at Equilibrium

[A-] at Equilibrium

[HA] at Equilibrium

0.000167

pKa3.78

Ka vs [H+] at Equilibrium

View formula & how it works →

How to Calculate Ka

Formula

Ka = [H+][A-] / [HA]

For the equilibrium: HA <-> H+ + A-

Example Calculation

At equilibrium: [H+]=0.004, [A-]=0.004, [HA]=0.096 M.

01Ka = (0.004 × 0.004) / 0.096
02Ka = 0.000016 / 0.096
03Ka = 1.67 × 10^-4
04pKa = -log10(1.67 × 10^-4) = 3.78

Frequently Asked Questions

Learn More

Understanding Molarity

Learn what molarity is, how to calculate it, and why it matters in chemistry. Covers moles, liters, dilution, and step-by-step examples for preparing solutions.

Related Calculators

Kb Calculator

Calculate base dissociation constant.

pKa Calculator

Calculate pKa from Ka.

Buffer pH Calculator

Calculate buffer pH.