Let's solve the problem step by step.
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Problem:
Write the name of the ionic compound:
Fe(OH)₃
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Step 1: Identify the ions present
The compound
Fe(OH)₃ consists of:
-
Fe: Iron (a transition metal)
-
(OH)₃: Three hydroxide ions
From the table provided:
-
OH⁻ is the
hydroxide ion (a polyatomic ion with a -1 charge)
So, each OH⁻ has a -1 charge.
Since there are
three OH⁻ ions:
Total negative charge = 3 × (-1) =
-3
To balance this, the iron ion must have a
+3 charge to make the compound neutral.
Therefore, the iron ion is
Fe³⁺.
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Step 2: Determine the name of the cation
Iron (Fe) is a
transition metal, which means it can form more than one type of ion (variable oxidation states). So we must specify its charge using
Roman numerals in parentheses.
Since Fe is
+3, we write
iron(III).
> Note: The Roman numeral indicates the charge of the metal ion.
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Step 3: Name the anion
The anion is
OH⁻, which is called
hydroxide.
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Step 4: Combine the names
Now, combine the cation and anion names:
- Cation:
Iron(III)
- Anion:
Hydroxide
So, the full name is:
>
Iron(III) hydroxide
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✔ Final Answer:
Iron(III) hydroxide
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🔍 Explanation Summary:
- The formula Fe(OH)₃ shows three hydroxide ions (each -1), so total charge = -3.
- Therefore, Fe must be +3 → Fe³⁺.
- Since iron is a transition metal, we use Roman numerals to indicate its charge.
- The name includes the metal name followed by the charge in parentheses, then the anion name.
✔ This naming follows IUPAC rules for ionic compounds with variable-charge metals.
Parent Tip: Review the logic above to help your child master the concept of naming polyatomic ions worksheet.
