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<big><font size="2"><big>The textbook states NH3 is an Arrhenius
base.<br>
<br>
The book is technically incorrect. The original definition
stated<br>
that OH- was part of the compound and that compound when put<br>
in water released the OH-, making the solution basic (inc. the
conc.<br>
of OH-). This theory wasn't able to correctly explain why NH3
was<br>
a base. Instead people came up with the nonexistent substance<br>
ammonium hydroxide, NH4OH, which has an OH- in the formula.<br>
This really doesn't exist. If you put NH3 in H2O you get NH4+
ions<br>
and OH- ions, which we can see using Bronsted-Lowry Theory.<br>
However, if you allow the water to evaporate you don't get a
compound<br>
of ammonium hydroxide. Instead what happens as the water<br>
vaporizes is the NH3 slowly comes out of soln as a gas (which
it is<br>
to begin with) and you will eventually be left with nothing
but air.<br>
<br>
A looser definition, what the book uses, is an Arrhenius base
is<br>
any substance that increases the conc. of OH- in an aqueous
soln.<br>
NH3 does inc. the conc. of OH-. But again, this does not
strictly<br>
fit the definition of an Arrhenius base. Using this criteria
any<br>
anion that acts as a base would be considered an Arrhenius
base<br>
(such as F- and no books state this is so).<br>
<br>
By the way, you will often see on a bottle of aqueous NH3 the
name<br>
ammonium hydroxide. This is a misnomer (as I explained above)
but<br>
has kind of stuck for the name of an aqueous solution of NH3.<br>
<br>
Here's a link which also describe this,<br>
<br>
<a class="moz-txt-link-freetext"
href="http://www.chemteam.info/AcidBase/Arrhenius-AcidBase.html">http://www.chemteam.info/AcidBase/Arrhenius-AcidBase.html</a><br>
<br>
This technically applies to other things as well. According
to his<br>
original theory the base had to have an OH (technically, OH-)
in<br>
the formula. This means the answer in the solutions manual on<br>
Carmen to 16.14(b) is technically not correct.<br>
<br>
Dr. Zellmer</big></font></big>
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