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)