First, let's deal with the ions, then the compounds (salts) that can be made from them.
During the middle of the previous course (CH 105) when we were studying acids and
talked about the nomenclature of acids, we spent some time talking about how to name the
negative ions formed by acids such as sulfuric acid and nitric acid. I would like to take
a little bit of time now to review that.
|It is actually quite simple. If you know the name of the acid, all you
have to do is remove the -ic from the acid's name and replace it with -ate.
|The same holds true for carboxylic acids.
They dissociate to give carboxylate ions. This same method holds for the
IUPAC names as well as common names of these acids. Some of these are shown here (and in
Example 5 in your workbook).
|Formic acid, when neutralized or ionized, will result in formate
ion. Using the IUPAC name, methanoic acid gives methanoate ion.
|Acetic acid will result in the formation of acetate ion.
Ethanoic acid gives ethanoate ion.
|Propionic acid, which is a common name for propanoic acid, will result in
the formation of propionate ion or propanoate ion to use
the IUPAC name.
|Butyric acid results in the formation of butyrate ion.
Butanoic acid gives butanoate ion.
I might also point out that the condensed structural formulas of the acids and ions
shown here do not specifically show the double bond between carbon and one of the oxygen
atoms. The use of condensed structural formulas presumes that you can figure this out.
Also, sometimes -CO2H is used in place of -COOH for the acids and sometimes -CO2-
is used in place of -COO- for the ions.
You name carboxylate salts in the same way that you do for other salts.
|Sodium acetate is such a salt. The formula for sodium acetate is given
here (and in Example 9-a). It simply combines sodium ion with acetate ion. So the formula
could be written NaCH3CO2.
|There are other ways that you might see the formula written.
For example, you might have the sodium at the oxygen end of the formula. The reason for
doing that would be to emphasize that the positive sodium ion is attached to the negative
end (the oxygen end) of the acetate ion.
Again, note that the two oxygen atoms can be written in different ways. In a condensed
structural formula, the two oxygen atoms that are bonded to the carbon atom, the oxygen
with the double bond and the oxygen with the single bond, can be written as O2
or they can be written separately as OO. Either way is quite acceptable.
|Another compound that you may have heard about is calcium propionate. The
formula for calcium propionate would have a calcium ion and two propionate ions. It has
two propionate ions because each one has a negative charge and calcium has a +2 charge.
Again, a couple different ways of writing this formula. One is calcium with the
condensed structural formula for the ion. The other way of showing this is calcium with
what could be called the "molecular" formula for the ion in which all the carbon
atoms are listed together, rather than showing how the atoms are arranged, C3H5O2-.
This "molecular" formula is not a particularly good way of writing the formula
because it does not show how the atoms are arranged. However, it does take up less room
and it is correct.
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