pKa converter
Convert pKa to the dissociation constant it stands for, and to pKb. Each unit of pKa is a tenfold change in strength.
That's about the same as acetic acid. That is a moderately strong acid, the range of the carboxylic acids.
What it means
How strong is that acid?
Values are for water at 25 °C. pKa shifts with solvent and temperature, and in a protein an ordinary side chain can move several units.
Every unit
Your acid strength in every unit
Learn
Three things worth knowing
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At pH = pKa, it is half dissociated
That is the Henderson–Hasselbalch equation in one line, and it is why a buffer is strongest within about one unit of its pKa.
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Logarithms tame the range
Ka values run from 10² to 10⁻¹⁶. Taking the negative logarithm turns that unmanageable span into the −2 to 16 that fits on a page.
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Lower means stronger
Acetic acid at 4.76 is far weaker than sulfuric at −3, despite the bigger number. The scale runs backwards, like magnitudes of stars.
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Background
About pKa
pKa is the negative logarithm of the acid dissociation constant, so a lower pKa means a stronger acid. At a pH equal to the pKa, exactly half the molecules have given up their proton — which is what makes buffers work.