Question

What is the Arrhenius concept of acidity?

Answer 1

Old Arrhenius conceived the acidium ion to be `H^+`.......

Explanation:

And the autoprotolysis reaction of water was proposed to be:

`H_2O(l) rightleftharpoons H^(+) + HO^-`

And so for the stoichiometric equation:

`Ba(OH)_2(s) + 2HCl(aq) rarr BaCl_2(aq) + 2H_2O`

We could write the net ionic equation:

`HO^(-) + H^(+) rarr H_2O`

Clearly, stoichiometry requires that we add 2 equiv hydrochloric acid per equiv barium hydroxide.

Answer 2

This could be written in two different ways, depending on whether you consider the barium hydroxide to be in solid form or solution form.

Explanation:

In Arrhenius' view, the HCl solution would be a mixture of `H^+` and `Cl^-` ions.

Barium hydroxide is slightly soluble, so you could write is in aqueous form or as a solid. Here is the former:

`H^+ + Cl^-` `+ Ba^(2+) + OH^-` `rarr Ba^(2+) + Cl^- + H_2O`

To balance this, you note that `Ba(OH)_2` has two hydroxide ions, and requires two hydrogen ions for complete reaction:

`2H^+ + 2Cl^-` `+ Ba^(2+) + 2OH^-` `rarr Ba^(2+) + 2Cl^- + 2H_2O`

Or, if the net ionic equation is desired, leave out the `Ba^(2+)` and `Cl^-` ions. (They do not change during the reaction.)

`2H^+ +2OH^-` `rarr 2H_2O`

which of course, is the neutralization reaction.

If you write the reaction showing barium hydroxide as a solid, it looks like this:

`2H^+ + 2Cl^-` `+ Ba(OH)_2(s) rarr Ba^(2+) + 2Cl^- + 2H_2O`