What is the formula of Iron (III) oxide?

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Study for the IGCSE Edexcel Chemistry Test. Access flashcards and multiple choice questions with hints and explanations. Get ready for your exam!

Multiple Choice

What is the formula of Iron (III) oxide?

Explanation:
The key idea is balancing charges to form a neutral compound. In iron(III) oxide, iron is in the +3 oxidation state and oxide is O2−. To balance +3 with −2, you need two iron ions and three oxide ions: 2×(+3) + 3×(−2) = +6 − 6 = 0. This gives Fe2O3, the formula for iron(III) oxide, the substance known as rust. If it were FeO, iron would be in the +2 state; Fe3O4 contains both +2 and +3 states (iron(II,III) oxide); and FeO2 would imply a different, less common oxidation state for iron.

The key idea is balancing charges to form a neutral compound. In iron(III) oxide, iron is in the +3 oxidation state and oxide is O2−. To balance +3 with −2, you need two iron ions and three oxide ions: 2×(+3) + 3×(−2) = +6 − 6 = 0. This gives Fe2O3, the formula for iron(III) oxide, the substance known as rust. If it were FeO, iron would be in the +2 state; Fe3O4 contains both +2 and +3 states (iron(II,III) oxide); and FeO2 would imply a different, less common oxidation state for iron.

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