# What is the Arrhenius concept of acidity?

Mar 31, 2017

Old Arrhenius conceived the acidium ion to be ${H}^{+}$.......

#### Explanation:

And the autoprotolysis reaction of water was proposed to be:

${H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s {H}^{+} + H {O}^{-}$

And so for the stoichiometric equation:

$B a {\left(O H\right)}_{2} \left(s\right) + 2 H C l \left(a q\right) \rightarrow B a C {l}_{2} \left(a q\right) + 2 {H}_{2} O$

We could write the net ionic equation:

$H {O}^{-} + {H}^{+} \rightarrow {H}_{2} O$

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

Mar 31, 2017

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 $C {l}^{-}$ ions.

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

${H}^{+} + C {l}^{-}$$+ B {a}^{2 +} + O {H}^{-}$$\rightarrow B {a}^{2 +} + C {l}^{-} + {H}_{2} O$

To balance this, you note that $B a {\left(O H\right)}_{2}$ has two hydroxide ions, and requires two hydrogen ions for complete reaction:

$2 {H}^{+} + 2 C {l}^{-}$$+ B {a}^{2 +} + 2 O {H}^{-}$$\rightarrow B {a}^{2 +} + 2 C {l}^{-} + 2 {H}_{2} O$

Or, if the net ionic equation is desired, leave out the $B {a}^{2 +}$ and $C {l}^{-}$ ions. (They do not change during the reaction.)

$2 {H}^{+} + 2 O {H}^{-}$$\rightarrow 2 {H}_{2} O$

which of course, is the neutralization reaction.

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

$2 {H}^{+} + 2 C {l}^{-}$$+ B a {\left(O H\right)}_{2} \left(s\right) \rightarrow B {a}^{2 +} + 2 C {l}^{-} + 2 {H}_{2} O$