Nomenclature
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Nomenclature

Ions

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.

Formulas for nitric acid and nitrate ion. [64str03.JPG]

 

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.
HCOOH

formic acid
methanoic acid

HCOO-

formate ion
methanoate ion

Acetic acid will result in the formation of acetate ion. Ethanoic acid gives ethanoate ion.
CH3COOH

acetic acid
ethanoic acid

CH3COO-

acetate ion
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.
CH3CH2COOH

propionic acid
propanoic acid

CH3CH2COO-

propionate ion
propanoate ion

Butyric acid results in the formation of butyrate ion. Butanoic acid gives butanoate ion.
CH3CH2CH2COOH

butyric acid
butanoic acid

CH3CH2CH2COO-

butyrate ion
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.

 

Salts

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.
sodium acetate NaCH3CO2
CH3COONa
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.
calcium propionate
or
calcium propanoate
Ca(CH3CH2CO2)2
Ca(C3H5O2)2

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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Clackamas Community College
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