How do you write Ka?

1 Answer
anor277
Aug 9, 2016

You mean the #"acid dissociation constant",K_a#?

Explanation:

#HA(aq) + H_2O(l) rightleftharpoons H_3O^+ + A^-#

Given that #[H_2O]# is effectively a constant, we can write the equilibrium expression in this way:

#K_a=([H_3O^+][A^-])/([HA])#

And thus for strong acids, where the equilibrium as written lies strongly to the right, #K_a# is large. #K_a# is small for weaker acids where the equilibrium lies to the left.

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