Overview
This lecture explains the rules for naming acids, including those with polyatomic and monoatomic ions, and how to write their chemical formulas from their names.
Naming Acids with Polyatomic Ions
- If the polyatomic ion ends in "-ate," replace with "-ic" and add "acid" (e.g., sulfate → sulfuric acid).
- If the polyatomic ion ends in "-ite," replace with "-ous" and add "acid" (e.g., sulfite → sulfurous acid).
- Common oxyacids: H₂SO₄ (sulfuric acid), H₂SO₃ (sulfurous acid), HClO₄ (perchloric acid), HClO (hypochlorous acid), HNO₃ (nitric acid), HNO₂ (nitrous acid), HC₂H₃O₂ (acetic acid).
Naming Acids with Monoatomic Ions (Binary Acids)
- For monoatomic ions ending in "-ide," use the prefix "hydro-" + root of element + "-ic acid" (e.g., H₂S → hydrosulfuric acid, HCl → hydrochloric acid, HI → hydroiodic acid, HBr → hydrobromic acid).
Writing Formulas from Acid Names
- Identify if "hydro" is present to distinguish between binary and oxyacids.
- For acids ending in "-ic," use the "-ate" form of the ion; for "-ous," use the "-ite" form.
- Add the appropriate number of hydrogens to balance the negative charge of the anion (e.g., phosphoric acid: phosphate is PO₄³⁻ so add three H⁺ to get H₃PO₄).
- Carbonic acid: CO₃²⁻ needs two hydrogens → H₂CO₃.
- For binary acids, pair H⁺ with the monoatomic anion (e.g., HBr for hydrobromic acid).
Exception Example
- Hydrocyanic acid is based on the polyatomic ion cyanide (CN⁻) despite "hydro-"; formula is HCN.
Key Terms & Definitions
- Acid — Compound that releases H⁺ ions in solution.
- Polyatomic ion — Ion with more than one atom (e.g., SO₄²⁻, NO₃⁻).
- Monoatomic ion — Ion with a single atom (e.g., Cl⁻, S²⁻).
- Oxyacid — Acid containing hydrogen, oxygen, and another element.
- Binary acid — Acid containing hydrogen and one other element.
- Suffix "-ic" — Used in acid names from "-ate" ions.
- Suffix "-ous" — Used in acid names from "-ite" ions.
- Prefix "hydro-" — Used for binary acids with "-ide" anions.
Action Items / Next Steps
- Memorize common polyatomic ions and their charges.
- Practice naming and writing formulas for acids using the provided rules.
- Complete any assigned problems on acid nomenclature.