The Equilibrium Constant for an acid (Ka) calculator computes Ka based on the concentration of free floating protons [H3O+], conjugate base [A-] and the weak acid added to the solution [HA].
INSTRUCTION: Choose units and enter the following:
Equilibrium Constant for an acid (Ka) : The calculator returns the constant in moles per liter.
Ka = [H3O+]•[A-] / [HA]
The Equilibrium Constant for an acid (Ka) is found using the equation Ka = [H3O+][A-] / [HA], with [H3O+] representing the free floating protons, [A-] the conjugate base, and [HA] the original weak acid added to solution. Ka refers to the dissociation of a weak acid in solution, and uses the Brönsted-Lowry definition of an acid, as opposed to Arrhenius. The inputs are the molarity of the hydronium [H3O+], the conjugate base [A-], and the acid [HA]. 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 acid dissociation constant is unitless.
Ka is useful for biochemists and organic chemists among others, but can also prove useful in any situation involving or requiring pH or pOH. The base equilibrium constant Ka can be used in the following constant formula, Kw = Ka * Kb, to solve for Kb, which in turn can be used to find pOH. Since Kw is a constant with a value of 1.00 x 1014, if either Kb or Ka is known, then the other equilibrium constant can be calculated. Similarly, Ka can be used to find the pH of a solution.
Whitten, et al. "Chemistry" 10th Edition. Pp. 734
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