The chemical formula for iron(II) nitrate is
a. Fe2(NO3)3
b. Ir(NO2)2
c. Fe2N3
d. Fe(NO3)2
e. Fe(NO2)2
The Correct Answer and Explanation is:
The correct answer is:
d. Fe(NO₃)₂
Explanation:
Iron(II) nitrate is an ionic compound consisting of the Iron(II) ion (Fe²⁺) and the nitrate ion (NO₃⁻). To determine the correct formula, it’s important to understand both the charge balance and the nomenclature rules for ionic compounds.
Step 1: Understand the Ions Involved
- Iron(II) refers to the iron ion with a +2 charge, or Fe²⁺.
The Roman numeral (II) in the name indicates this oxidation state. - Nitrate is a polyatomic ion with the formula NO₃⁻ and carries a -1 charge.
Step 2: Determine the Correct Ratio
Since Fe²⁺ has a +2 charge and NO₃⁻ has a -1 charge, we need two nitrate ions to balance the charge of one iron(II) ion:
$$
\text{Fe}^{2+} + 2(\text{NO}_3^-) \rightarrow \text{Fe(NO}_3)_2
$$
This ensures the compound is electrically neutral, which is a requirement for all stable ionic compounds.
Step 3: Analyze the Incorrect Options
- a. Fe₂(NO₃)₃: This is the formula for iron(III) nitrate, which contains Fe³⁺ ions, not Fe²⁺.
- b. Ir(NO₂)₂: This uses Iridium (Ir) and nitrite (NO₂⁻), not iron or nitrate.
- c. Fe₂N₃: This suggests a compound of iron and nitrogen, not nitrate.
- e. Fe(NO₂)₂: This is iron(II) nitrite, which contains nitrite (NO₂⁻), not nitrate (NO₃⁻).
Conclusion
The correct formula, Fe(NO₃)₂, reflects:
- The Fe²⁺ ion (Iron(II))
- The NO₃⁻ ion (nitrate)
- The proper charge balance: +2 from iron and 2 × -1 from two nitrate ions