K in Ka

[Chris_Strickhouser_1A]

Why does the “K” in KA mean that the acid is a weak acid? In other words, how do we know the acid is weak just by looking at the “K”?

[Tricia Tran 1G]

If the acid is strong, it would completely dissociate so you can just calculate the [H3O+] or pH or whatever the question asks for just by looking at the initial concentration of the acid. For weak acids, you would need an ICE table to calculate [H3O+] or pH at equilibrium since the acid does not completely dissociate. To do this, you would need the Ka value. Therefore, a quick trick is that if you are given the Ka value, you know that the acid should be weak.

[BeauBrown]

You can use pKa (-log[Ka]) to see what acid/base is strong. Just like pH, the lower the stronger.

[yvette nouneh]

If you have a high value of Ka, which would correspond to a small pKa value, you know that the acid is strong. If you have a low value of Ka, which would correspond to a large pKa value, you would know that the acid is weak.