How do you calculate the Ka of an acid?

1 Answer
Jul 10, 2017

Answer:

#K_a# applies to weak acids in aqueous solution

Explanation:

For a hypothetical weak acid #HA rightleftharpoons H^+ + A^-#

#K_a = (([H^+][A^-])/[HA])# where #[H^+], [A^-] & [HA]# are molar concentrations of hydronium ion, conjugate base and weak acid at equilibrium.

Example:
Given a 0.10M weak acid that ionizes ~1.5%
#[H^+] = [A^_] = 0.015(0.10)M = 0.0015M#
#[HA] ~~ 0.10M - 0.0015M~~ 0.0985M#

#K_a = (([H^+][A^-])/[[HA]]) = ((0.0015)(0.0015))/(0.0985)# = #2.28xx10^-4#