Which of the following is the correct chemical formula for iron(III) sulfide?

• A. FeSO3
• B. FeS
• C. Fe3S2
• D. Fe2S3

Answer: (D)

Verified step by step guidance

1. Identify the oxidation state of iron in iron(III) sulfide. The (III) indicates that iron has a +3 charge, so Fe is Fe^{3+}.
2. Determine the charge of the sulfide ion. Sulfide (S) typically has a charge of 2-, so S is S^{2-}.
3. Balance the total positive and negative charges to find the correct ratio of Fe^{3+} to S^{2-}. The goal is to have the total positive charge equal the total negative charge.
4. Set up the charge balance equation: 3x (charge of Fe^{3+}) times number of Fe atoms = 2x (charge of S^{2-}) times number of S atoms. This can be written as 3a = 2b, where a and b are the subscripts for Fe and S respectively.
5. Find the smallest whole number ratio that satisfies 3a = 2b. This ratio gives the chemical formula Fe_{2}S_{3}.