What are some common mistakes students make with Arrhenius acids?
There is one error only, and it is a teacher's one: to teach Arrhenius' definition of acids.
She should involve her students with Bronsted-Lowry definition. An Arrhenius acid is a species liberating H+ ions in water solution, whereas a B&L acid is a species which may donate a proton to another species in every milieu.
There really isn't one, hopefully; it's very simple. The only thing you need to know about Arrhenius acids is that they dissociate in water to give