To name the ionic compound
Fe(OH)₃, we follow the rules for naming ionic compounds, especially those involving transition metals (like iron, Fe), which can have multiple possible charges.
---
Step 1: Identify the ions
- The compound is made of
Fe (iron) and
OH⁻ (hydroxide ion).
- From the table provided,
OH⁻ is called
hydroxide.
- Iron (Fe) is a
transition metal, so it can form more than one type of cation — commonly
Fe²⁺ (iron(II)) or
Fe³⁺ (iron(III)).
---
Step 2: Determine the charge on the iron ion
The formula is
Fe(OH)₃.
- Each
OH⁻ ion has a
-1 charge.
- There are
3 hydroxide ions, so total negative charge = 3 × (-1) =
-3.
- Since the compound is neutral, the iron ion must have a
+3 charge to balance it.
→ So, the iron ion here is
Fe³⁺.
---
Step 3: Name the compound
For transition metals with variable charges, we use
Roman numerals in parentheses to indicate the charge of the metal ion.
- Cation:
Iron(III) (because Fe³⁺)
- Anion:
Hydroxide
Combine them:
>
Iron(III) hydroxide
---
✔ Final Answer:
Iron(III) hydroxide
---
💡 Note:
You might sometimes see older names like “ferric hydroxide,” but the modern IUPAC naming system uses Roman numerals — so
Iron(III) hydroxide is the correct and preferred name.
Parent Tip: Review the logic above to help your child master the concept of nomenclature worksheet 3 ionic compounds containing polyatomic ions.
