What is the Arrhenius concept of acidity?
Old Arrhenius conceived the acidium ion to be
And the autoprotolysis reaction of water was proposed to be:
And so for the stoichiometric equation:
We could write the net ionic equation:
Clearly, stoichiometry requires that we add 2 equiv hydrochloric acid per equiv barium hydroxide.
This could be written in two different ways, depending on whether you consider the barium hydroxide to be in solid form or solution form.
In Arrhenius' view, the HCl solution would be a mixture of
Barium hydroxide is slightly soluble, so you could write is in aqueous form or as a solid. Here is the former:
To balance this, you note that
Or, if the net ionic equation is desired, leave out the
which of course, is the neutralization reaction.
If you write the reaction showing barium hydroxide as a solid, it looks like this: