Introduction to Hydroxides
Hydroxides are inorganic compounds formed by a metal bonded to the hydroxide group (OH⁻). They are basic compounds that release OH⁻ ions in aqueous solution.
Nomenclature using prefixes
Multiplicative prefixes indicate the number of atoms of each element: mono-, di-, tri-, tetra-, penta-, hexa-, etc.
Examples:
- NaOH: sodium hydroxide
- Fe(OH)₂: iron(II) hydroxide
- Fe(OH)₃: iron(III) hydroxide
- Pb(OH)₄: tin(IV) hydroxide (lead(IV) hydroxide where applicable)
Nomenclature by oxidation state
Hydroxide carries a -1 charge per OH group and the oxidation state of the other element is indicated using Roman numerals or numbers in parentheses.
To determine the oxidation state, multiply -1 by the number of hydrogens (OH groups) to get the total negative charge. That negative charge is balanced by the positive charge of the other element; divide by the number of atoms of that element to obtain its oxidation state.
Elements that typically have a single oxidation state (alkali metals +1, alkaline earth metals +2, aluminum +3) often omit the oxidation state in the name.
Examples:
- Fe(OH)₂: iron(II) hydroxide
- Fe(OH)₃: iron(III) hydroxide
- Pb(OH)₄: lead(IV) hydroxide
- Ca(OH)₂: calcium hydroxide (oxidation state often omitted)
- NaOH: sodium hydroxide (oxidation state omitted)
| Formula | IUPAC Name | Common Name |
|---|---|---|
| NaOH | Sodium hydroxide | Caustic soda |
| Ca(OH)₂ | Calcium hydroxide | Slaked lime |
| Fe(OH)₃ | Iron(III) hydroxide | — |
| Al(OH)₃ | Aluminum hydroxide | — |
| Mg(OH)₂ | Magnesium hydroxide | Milk of magnesia |
| Cu(OH)₂ | Copper(II) hydroxide | — |
| KOH | Potassium hydroxide | Caustic potash |
| Ba(OH)₂ | Barium hydroxide | — |