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Chemistry · Glossary

What is Acidity constant?

Definition 10.4 University Chemistry — Year 1 · Chapter 10 — Acid–Base Equilibria and the Predominant-Reaction Method

The acidity constant of a couple HA/A is the constant of the reaction of the acid with water,

HA+HX2O⇌A+HX3OX+,Ka=[A][HX3OX+][HA],pKa=−log⁡Ka.\mathrm{HA} + \ce{H2O} \rightleftharpoons \mathrm{A} + \ce{H3O+}, \qquad K_a = \frac{[\mathrm{A}][\ce{H3O+}]}{[\mathrm{HA}]}, \qquad \mathrm{p}K_a = -\log K_a .

The larger KaK_a (the smaller pKa\mathrm{p}K_a), the stronger the acid and the weaker its conjugate base.

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