Use the Bronsted-Lowry definitions to identify the two conjugate acid-base pairs in the following acid-base reaction:

Question

H20 + H20 <-> H30^+ + OH^-

Let's see what you think on this after the previous post. Just remember, the acid is the one that HAS the H and the base is the one that TAKES the H.

But they all have an H in them? How would I know then, which one is the acid and which one is the base?

I agree this is not that clear cut; however, the H3O^+ is a clue. That MUST have come from H2O; therefore, one of the H2O molecules gave a H to the other one to form H3O^+ and that leaves a OH^- ion.

I think the point of this question is to show you that H2O can be an acid while H2O is being a base.