Tuesday, August 23, 2011

Acids Nomenclature

Let’s deal with these compounds now, many must have heard about acids at some point, on a movie, or in jokes; but everything points to their destructive capability.
The following acids are Oxacids, as they have oxygen in their structure; there is another kind of acids, the hydroacids that only have the Non-Metal and the Hydrogen.

Acids are formed when Non-Metal Oxides (also known as Anhydrides) react with Water.
SO3      +       H2O     ------>      H2SO4
Acid formulas are a bit tricky to make, but with a little practice it becomes very easy.
First as usual, I'm going to start with the formula writing structure:

H Non-Metal O

As you can see the Hydrogen comes first, then the No-Metal and the Oxygen is last.
Most of the Acids have only subscripts on the Hydrogen and Oxygen but some rare have it on the No-Metal aswell.

HA MetalC OB

There are many ways to figure out the subscripts; I'm going to teach you the easiest one in my opinion.
Write down the elements in the correct order. (2 examples)

H S O                                              H Cl O
Now check the valence of the No-Metal you are going to use, is it an EVEN or ODD number. (For valences check this page: Valences)
  • If it is EVEN ---->the HYDROGEN’s SUBSCRIPT is 2
  • If it is ODD ---->the HYDROGEN’s SUBSCRIPT is 1
S ---> Ox # = +2 +4 +6
(Let’s do the formula for the valence +4)

H2 S O  

Cl ---> Ox # = +1 +3 +5 +7
(Let’s do the formula for the valence +3)
H1Cl O  
There's no need to write the subscript if its 1

Now here is the trick part: SUM the OXIDATION NUMBER of the Non-Metal with the HYDROGEN SUBSCRIPT
Now take this number and divide it by 2, this is now the OXYGEN’s SUBSCRIPT; weird isn't it? but this is the best way to do it.


There are 3 ways of naming Acids.
  • TRADITIONAL nomenclature
  • IUPAC nomenclature
  • STOCK nomenclature
IUPAC and STOCK nomenclature in acids is not used frequently, as it is a bit difficult and general chemical compound markets in the most part use only the TRADITIONAL nomenclature. 

You need to learn a little system of prefixes and suffixes (for the oxidation numbers)

Note that the suffix does not depend on the number but on how many valences the element has.


Name this Acid


Remember how to make Acid formulas? Now we just need to go backwards to figure out which oxidation number the metal is using. Take the oxygen subscript, multiply it by 2 and subtract the Hydrogen subscript.

Now that we know which it is, let’s find the correct suffix to use. It has 4 oxidation numbers:

+1 ----> Hip-----ous
+3 ----> -ous
+5 ----> -ic
+7 ----> Per------ic

Traditional nomenclature has this writing structure:


So we just need to fill the name of the Non-metal and the suffix

PerChloric Acid

Coming up! Acids Exercises


Hento the loony repairman :D said...

mmnh i was an ace at dojng this in high school. but later forgot due to not needing this in real life (in my field) but i want to get back on track XD, keep the head working :D

Anonymous said...

I got a science book out from the library; totally gonna learn all this stuff, EZPZ. :P

Liaata said...

nice post, thanks. guess i learned something :D

H's Corner said...

I'm studying engineering. I found this soooo boring.
But you explained it well! You're better than my teacher.


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