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                                                                                                                                                      Last updated:  02/09/2010

            

     
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                                        Recognizing an Acid                   update: 6/10/03

At this very beginning level, you will recognize an acid by the fact that its formula starts with H⁺¹, as in these examples:

HCl
HNO₃
H₂SO₄
HClO₃
H₃BO₃

As you become more sophisticated in your chemistry, you will realize that there are many acid formulas that do not start with H.

There is one exception to this: the formula CH₃COOH should be recognized as acetic acid. The particular way it is written is common in organic chemistry. An alternate way to write acetic acid is HC₂H₃O₂. This is done in the inorganic style which you are currently studying.

The formula H₂O should not be considered an acid. It is the formula for water.

Naming Acids

In order to explain acid naming, the sequence of HCl, HClO, HClO₂, HClO₃, and HClO₄ will be discussed in order.

All binary acids are named the same way:  

- The name for HCl is hydrochloric acid. 
- Other binary acids you are responsible for are HF, HBr, HI, and H₂S.

1. the prefix "hydro" is used.
2. the root of the anion is used.
3. the suffix "ic" is used.
4. the word "acid" is used as the second word in the name.
   

                                                        Acid involving a polyatomic ion:


Generally acids with -ate (polyatomic groups) endings are named "___ic" acids.
Generally acids with  -ite (polyatomic groups) endings are named " __ous" acids.

1) HClO is an acid involving a polyatomic ion. You MUST recognize the polyatomic ion in the formula. There is no other way to figure out the name. If you don't recognize the polyatomic, then you're sunk without a trace.

The polyatomic ion is ClO¯ and its name is hypochlorite. Any time you see the "ite" suffix, you change it to "ous" and add the word acid.

The name of HClO is hypochlorous acid.

2) HClO₂ has the ClO₂¯ polyatomic ion in it. The name of this ion is chlorite.

Since the "ite" suffix is used, it gets changed to "ous."

The name of HClO₂ is chlorous acid.

3) HClO₃ has the ClO₃¯ polyatomic ion and its name is chlorate. Any time you know the "ate" ending is used on the polyatomic, you use "ic" when you write the corresponding acid formula.

The name of HClO₃ is chloric acid.

4) HClO₄ has the ClO₄¯ polyatomic ion and its name is perchlorate.

Since the "ate" suffix is used, it gets changed to "ic."

The name of HClO₄ is perchloric acid.

Practice Problems