Arrhenius Acid-Base Theory and NH3

[Zellmer, Robert]

I mentioned this in lecture.  The textbook states NH3 is an
Arrhenius base.  Someone had a question about this.

The book is technically incorrect.  The original definition stated
that OH- was part of the compound and that compound when put
in water released the OH-, making the solution basic (inc. the conc.
of OH-).  This theory wasn't able to correctly explain why NH3 was
a base.  Instead Arrhenius came up with the nonexistent substance
ammonium hydroxide, NH4OH, which has an OH- in the formula.
This actually doesn't exist.  If you put NH3 in H2O you get a few
NH4+ ions and OH- ions, which we can see using Bronsted-Lowry
Theory, but most of it remains as dissolved NH3 (in a 1 M NH3 soln
only 1.33 % has reacted and 98.67 % remains as NH3).
If you allow the water to evaporate you don't get a compound
of ammonium hydroxide.  Instead what happens as the water
vaporizes is the NH3 slowly comes out of soln as a gas (which it is
to begin with).   You are left with nothing but air in the container.

A looser definition, what the book uses, is an Arrhenius base is
any substance that increases the conc. of OH- in an aqueous soln.
NH3 does inc. the conc. of OH-.  But again, this does not strictly
fit the definition of an Arrhenius base.  Using this criteria any
anion that acts as a base would be considered an Arrhenius base
(such as F- and no books state this is so).

By the way, you will often see on a bottle of aqueous NH3 the name
ammonium hydroxide (NH4OH).  This is a misnomer (as I explained above)
but has kind of stuck for the name of an aqueous solution of NH3.

Here's a link which also describe this,

http://www.chemteam.info/AcidBase/Arrhenius-AcidBase.html

Below are some more interesting links dealing with this and
Arrhenius (quite prolific scientist).  I don't necessarily like using
Wikipedia as a direct reference but you can find other links there
to check on things.

https://h2g2.com/edited_entry/A708257

https://h2g2.com/edited_entry/A692796

https://en.wikipedia.org/wiki/Svante_Arrhenius

https://en.wikipedia.org/wiki/Base_(chemistry)<https://en.wikipedia.org/wiki/Base_%28chemistry%29>

This technically applies to other substances as well.  According to his
original theory the base had to have an OH (technically, OH-) in
the formula.  This means the answer in the solutions manual on
Carmen to 16.14(b) (13th, 12th & 10th ed.), 16.16(b) (11th ed.) is
technically not correct.

Dr. Zellmer
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