What is the formula of the compound consisting of iron(II) and nitrite ions.
A. Fe2NO2
B. Fe(NO3)2
C. Fe2N
D. Fe(NO2)2
E. Fe2NO3
The Correct Answer and Explanation is:
The correct answer is: D. Fe(NO₂)₂
Explanation:
To determine the correct formula for a compound consisting of iron(II) and nitrite ions, we need to understand the charges of each ion and how to combine them to form a neutral compound.
1. Understanding the Ions Involved
- Iron(II) ion (Fe²⁺):
The Roman numeral (II) indicates that iron has a +2 charge.
So, the iron(II) ion is written as Fe²⁺. - Nitrite ion (NO₂⁻):
The nitrite ion is a polyatomic ion with a -1 charge.
It is written as NO₂⁻.
2. Combining the Ions to Form a Neutral Compound
To create a neutral compound, the total positive and negative charges must balance.
- Fe²⁺ has a +2 charge.
- NO₂⁻ has a -1 charge.
To balance the +2 charge of one iron(II) ion, we need two nitrite ions: Fe2++2NO2−→Fe(NO2)2\text{Fe}^{2+} + 2\text{NO}_2^- \rightarrow \text{Fe(NO}_2)_2
Thus, the chemical formula is Fe(NO₂)₂.
3. Eliminating Incorrect Options
- A. Fe₂NO₂ — Incorrect. This implies two Fe atoms and one NO₂ group, which does not balance the charges.
- B. Fe(NO₃)₂ — Incorrect. This contains nitrate (NO₃⁻), not nitrite (NO₂⁻).
- C. Fe₂N — Incorrect. This would be a compound with nitride (N³⁻), not nitrite.
- D. Fe(NO₂)₂ — ✅ Correct. One Fe²⁺ ion and two NO₂⁻ ions balance the charges.
- E. Fe₂NO₃ — Incorrect. This is not a valid representation and uses nitrate instead of nitrite.
Conclusion
The correct formula for a compound made of iron(II) and nitrite ions is Fe(NO₂)₂, as it properly reflects the charges and number of ions needed to create a neutral ionic compound.