Base Equilibrium Constant (Kb)

The Equilibrium Constant for a base (K_b) is found using the equation K_b = [BH⁺][OH^-] / [B], with [BH⁺] representing the protonated base, [OH^-] the hydroxide ions, and [B] the original base added to solution. K_b refers to the dissociation of a base in solution, and uses the Brönsted-Lowry definition of a base, as opposed to Arrhenius. The inputs are the concentration of the protonated base [BH⁺], the hydroxide ions [OH^-], and the unchanged base [B]. While this version of the equation uses molarity, a more complete definition uses molar activity instead of molarity. Molar activity accounts for both the molarity and non-ideal conditions. Molar activity is a unitless term, therefore the base dissociation constant is unitless.

Uses

K_b is useful for biochemists, but can also prove useful in any situation involving or requiring pH or pOH. The base equilibrium constant K_b can be used in the following constant formula, K_w = K_a * K_b, to solve for K_a, which in turn can be used to find pH. Since K_w is a constant with a value of 1.00 x 10¹⁴, if either K_b or K_a is known, then the other equilibrium constant can be calculated. Similarly, K_b can be used to find the pOH of a solution.

References

Whitten, et al. "Chemistry" 10th Edition. Pp. 734

Wikipedia: Equilibrium constant

Chemistry.osu

Ausetute.com, ChemTeam

See also:

Acid Equilibrium Constant (for the Spanish site click here)