- Acids are covalent compounds that release hydrogen ions in water. Their names are determined by specific nomenclature rules. - There are two categories of acids: binary acids containing hydrogen and one other atom type, and oxy-acids containing hydrogen and a polyatomic ion. - Binary acids are named with the prefix "hydro-" followed by the other atom's name ending in "-ic". Oxy-acids do not use "hydro-" and change the polyatomic ion's name ending to "-ic".

1. Acid Nomenclature

2. Purpose
• Acids are a special class of covalent substances. As such, they have their
own set of rules for nomenclature. In this lesson, you will learn to identify
acids based on their formulas and name them accordingly.

3. Basic Definition of an Acid
• An acid is a covalent compound that when dissolved in water releases
hydrogen ions:
– Hydrochloric acid gas splits into hydrogen ions and chloride ions when
dissolved in water
HCl (g)  H+ (aq) + Cl-(aq)

4. Acid formulas often begin with H
• Some common acids:
– HNO3
– HCl
– H2SO4
• Notice how each formula begins with H. While this is not an absolute rule,
for now it makes it easy to identify acids.

5. Acid Nomenclature
• There are two categories of acids we will deal with, and they are named
differently.
– Category 1: Binary acids – contain only H and one other type of atom
• Examples:
– HCl – hydrochloric acid
– H2S – hydrosulfuric acid
– Category 2: Oxy-acids – contain H with a polyatomic ion
• Examples:
– HNO3 – nitric acid
– H2SO4 – sulfuric acid

6. Category 1 Acids begin with hydro-
• For binary acids, we begin with hydro- and end the nonmetal in –ic.
• Examples:
– HCl – hydrochloric acid
– H2S – hydrosulfuric acid

7. Category 2 Acids DO NOT begin with hydro-
• For oxy-acids we DO NOT begin with hydro-. We change the ending on the
polyatomic ion. In this case, all of our polyatomic ions ended in –ate so we
change them to –ic.
• Examples:
– HNO3
» NO3
- = nitrate ion
» nitric acid
– H2SO4
» SO4
2- = sulfate ion
» sulfuric acid

8. Other oxyacids – keep in mind but not required
now.
• The oxyacids we looked at were all based on polyatomic ions ending in
-ate. If the polyatomic ion ends in -ite, the acid name ends in -ous
– -ate polyatomic ions
• NO3
- = nitrate ion
• HNO3 = nitric acid
– -ite polyatomic ions
• NO2
- = nitrite ion
• HNO2 = nitrous acid

9. Misconception Alert
• Look back at H2S and H2SO4 – one is hydrosulfuric acid and one is sulfuric
acid. For some reason, students have a really hard time remembering
when to use hydro-. For now, use hydro- only when the hydrogen is with
one other type of atom.
• Note: The actual rule is to use hydro- when the anion (negative ion left after the hydrogen is
removed) ends in –ide. In most cases this is a monatomic ion such as S2- or Cl-. There are a
couple polyatomic ions that end in –ide that do take hydro- when in acid form. You do not
need to worry about this now.

10. Pause and Practice
• What are the names of the following acids:
– HI
– H3PO4
– HF
– HClO4 (ClO4
- is the chlorate ion)

11. Pause and Practice
• What are the names of the following acids:
– HI
• Hydroiodic acid
– H3PO4
• Phosphoric acid
– HF
• Hydrofluoric acid
– HClO4 (ClO4
- is the perchlorate ion)
• Perchloric acid

12. Now try the exercises