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Naming Hydroxides
General Chemistry • Chemical Compounds
Frequently Asked Questions
How do you name hydroxides in ionic nomenclature?
Name the cation first, then add the word "hydroxide." If the metal has more than one possible charge, include a Roman numeral to show the oxidation state.
How is the Roman numeral determined in a metal hydroxide like Fe(OH)3?
Each OH group has charge -1, so three OH groups contribute -3 total. To make the compound neutral, Fe must be +3, so the name is iron(III) hydroxide.
When do you need parentheses around OH in a hydroxide formula?
Use parentheses when more than one hydroxide group is present, such as Ca(OH)2 or Al(OH)3. Parentheses are not needed when there is only one OH, such as NaOH or NH4OH.
Why is Al(OH)3 named aluminum hydroxide without a Roman numeral?
Aluminum is treated as a fixed-charge cation at +3 in common nomenclature, so a Roman numeral is not used. Variable-charge metals like iron or copper require the Roman numeral.
Does this tool work for hydroxides with polyatomic cations other than ammonium?
It is designed for metal hydroxides M(OH)n and ammonium hydroxide (NH4OH). More complex formulas may require broader polyatomic-ion naming rules.