Question

How do you write Ka?

Answer 1

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.