A Levels Chemistry (9701)•9701/11/O/N/21
Explanation
Stoichiometry ratios in metal oxide formation Steps:
- Balance the reaction equation for each element with O₂ to form its common oxide.
- Find the mole ratio of O₂ to element atoms from the balanced equation.
- Divide by the coefficient of the element to get moles of O₂ per 1 mol atoms.
- Compare ratios to find the minimum value.
Why D is correct:
- Sodium's reaction (4Na + O₂ → 2Na₂O) gives a 1:4 ratio of O₂ to Na atoms, so 0.25 mol O₂ per mol Na, the lowest per the stoichiometry law.
Why the others are wrong:
- A. Aluminum's reaction (4Al + 3O₂ → 2Al₂O₃) requires 0.75 mol O₂ per mol Al.
- B. Magnesium's reaction (2Mg + O₂ → 2MgO) requires 0.5 mol O₂ per mol Mg.
- C. Phosphorus's reaction (P₄ + 5O₂ → P₄O₁₀) requires 1.25 mol O₂ per mol P.
Final answer: D
Topic: Atoms, molecules and stoichiometry
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