Chemistry Regents Practice Test

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What is the chemical formula of iron(III) sulfide?

FeS
Fe2S3
Fe3S2
FeS2

The correct answer is: Fe2S3

The chemical formula of iron(III) sulfide is represented by the symbol Fe2S3. In this formula, the "Fe" stands for iron, and the "S" stands for sulfur. The subscript "2" next to iron indicates that there are two iron atoms for every three sulfur atoms in the compound. Iron(III) indicates that iron has a +3 oxidation state. Sulfur typically has a -2 oxidation state. To achieve a neutral compound, the total positive charge must equal the total negative charge. The two iron atoms contribute a total charge of +6 (2 x +3), while three sulfur atoms contribute a total charge of -6 (3 x -2). This balance confirms that the correct formula is indeed Fe2S3. Other formulas such as FeS represent iron(II) sulfide, where iron has a +2 oxidation state. Fe3S2 and FeS2 do not appropriately balance the charges for iron in the +3 oxidation state with the number of sulfur atoms required. Thus, when considering the oxidation states and ensuring overall charge neutrality, Fe2S3 is the accurate representation of iron(III) sulfide.