How is pka related to ka

All acid—base equilibria favor the side with the weaker acid and base. Thus the proton is bound to the stronger base. Two species that differ by only a proton constitute a conjugate acid—base pair.

For an aqueous solution of a weak acid, the dissociation constant is called the acid ionization constant Ka. Similarly, the equilibrium constant for the reaction of a weak base with water is the base ionization constant Kb.

Acid—base reactions always proceed in the direction that produces the weaker acid—base pair. Chem1 Virtual Textbook. When citing the strength of an acid, chemists often use the dissociation constant, Ka, but this number can vary by several orders of magnitude from one acid to another. If you already know the pKa value for an acid and you need the Ka value, you find it by taking the antilog.

In practice, this means raising both sides of the equality to exponents of In the Bronsted-Lowry formulation of acids in solution, the acid donates a proton and the solution accepts one. The solution becomes one containing a conjugate base — which is the product of the acid having lost a proton — and a conjugate acid. Theoretically, this reaction can happen in both directions.

When the solvent is water, this is written as:. It's possible to determine this strength of the original acid by dividing the concentrations of the conjugate acid and base by the concentrations of the original acid and base. When the solvent is water, it's left out of the equation. This operation gives you the dissociation constant Ka:. When Ka is large, it means the conjugate ions aren't strong enough to move the reaction in the opposite direction, which indicates a strong acid.

The dissociation constant for a strong acid can be as high as 10 7 , while for a weak acid it can be as low as 10 Ka and pKa review. Using pKa values to predict the position of equilibrium. Stabilization of a conjugate base: electronegativity. Acid strength, anion size, and bond energy. Stabilization of a conjugate base: resonance. Stabilization of a conjugate base: induction.