Naming Acids

Naming an acid from its formula requires us to recognize the basic structure of all acid formulas. Acids are similar to ionic compounds, in that they are made of positive and negative pieces. The difference is that the positive piece is always hydrogen ions (H⁺¹).

The name of the acid, then, is based on the negative ion alone. The names of negative ions always end in either "ate," "ite," or "ide." The name of the acid is related to the ending on that negative ion according to the system below. You will need to know your polyatomic ions for this.

ATE ions make IC acids

For example, the acid HNO₃ is a hydrogen attached to NO₃, which is called nitrate. (We know that nitrate has a -1 charge, although that's "invisible" because it is cancelled by the H⁺¹)
NitrATE makes nitrIC ACID. So HNO₃ is nitric acid.

Another example: H₂C₂O₄

ITE ions make OUS acids

The acid HNO₂ is a hydrogen attached to NO₂, which is called nitrite. (We know that nitrite has a -1 charge, although it's "invisible" because it is cancelled by the H⁺¹)
NitrITE makes nitrOUS ACID. So HNO₂ is nitrous acid.

Another example: HClO₂

IDE ions make HYDRO___IC acids

The acid HCN is a hydrogen attached to CN , which is called cyanide. (We know that cyanide has a -1 charge, but that's "invisible" because it is cancelled by the H⁺¹)
CyanIDE makes HYDROcyanIC ACID. So HCN is hydrocyanic acid.

Another example: H₂Se

Remember that an element from the periodic table with a negative charge gets the "ide" ending, so Se^-2 is selenide.

A note about acid names

Acids made from the ions sulfate, sulfite, sulfide, phosphate, phosphite and phosphide have a "quirk" in their name.
Sulfate (SO₄^-2) should make sulfic acid (following the system above), however we call it sulfuric acid (because it sounds better). The table below gives the correct names for each of these acids.

ion name	acid name
sulfate	sulfuric acid
sulfite	sulfurous acid
sulfide	hydrosulfuric acid
phosphate	phosphoric acid
phosphite	phosphorous acid
phosphide	hydrophosphoric acid

Your Turn

Try these on your own. The answers are here.

1. H₃PO₄
2. HBrO
3. HBr
4. HClO₄
5. HI
6. H₃P
7. HNO₂