Acid naming is a pattern-based system that lets chemists translate between a chemical formula and a clear compound name. It matters because acids appear in reactions, lab labels, safety instructions, and everyday substances such as vinegar and citrus juice. Once you recognize whether an acid contains oxygen, the naming rules become much easier to apply.
The key split is between binary acids and oxyacids.
Key Facts
- Binary acids contain hydrogen and one nonmetal: H + nonmetal.
- Binary acid names use hydro + nonmetal root + ic acid, such as HCl = hydrochloric acid.
- Oxyacids contain hydrogen, oxygen, and a polyatomic ion called an oxyanion.
- For oxyacids, anion ending -ate becomes -ic acid, such as NO3- to nitric acid.
- For oxyacids, anion ending -ite becomes -ous acid, such as NO2- to nitrous acid.
- The acid formula must be electrically neutral, so total H+ charge balances the anion charge, such as H2SO4 from 2H+ + SO4^2-.
Vocabulary
- Binary acid
- An acid made of hydrogen and one other nonmetal element, such as HBr or H2S.
- Oxyacid
- An acid made of hydrogen bonded to an oxygen-containing polyatomic ion, such as HNO3 or H2SO4.
- Oxyanion
- A negatively charged polyatomic ion that contains oxygen, such as nitrate, sulfate, or chlorite.
- Root name
- The shortened element or ion name used inside an acid name, such as chlor for chlorine or sulfur for sulfide.
- Neutral formula
- A chemical formula in which the total positive charge equals the total negative charge.
Common Mistakes to Avoid
- Adding hydro to every acid name is wrong because hydro is used only for binary acids that do not contain oxygen.
- Naming HNO3 as hydrogen nitrate is wrong in acid naming because nitrate changes to nitric acid when it is written as an aqueous acid.
- Changing -ate to -ous is wrong because oxyanion endings follow a fixed pattern: -ate becomes -ic and -ite becomes -ous.
- Forgetting to balance charge in name-to-formula problems is wrong because the number of H atoms must match the anion charge, such as H3PO4 for phosphate, PO4^3-.
Practice Questions
- 1 Name each acid: HCl, H2S, HBr.
- 2 Write the formulas for sulfuric acid, chlorous acid, and carbonic acid. Use these ions: SO4^2-, ClO2-, and CO3^2-.
- 3 A student names HClO3 as hydrochloric acid. Explain the error and give the correct name.