🧬 pKa Calculator
Convert an acid dissociation constant (Ka) into pKa, and estimate buffer pH from pKa and conjugate acid/base concentrations using the Henderson-Hasselbalch equation.
What is pKa?
pKa is a convenient logarithmic way to express how strong a weak acid is. It’s derived from the acid dissociation constant, Ka, which describes the equilibrium between a weak acid and its ions in water.
How this calculator works
pKa is calculated directly from Ka using:
pKa = −log10(Ka)
A smaller pKa means a stronger acid (more dissociation), while a larger pKa means a weaker acid. If you also enter the concentrations of the conjugate base and the remaining weak acid in a buffer solution, the calculator estimates the buffer’s pH with the Henderson-Hasselbalch equation:
pH = pKa + log10([A-] / [HA])
This equation is widely used to design and understand buffer solutions, which resist changes in pH. It works best when the buffer contains meaningful amounts of both the weak acid and its conjugate base. This tool is for general chemistry education purposes.