12 g of magnesium reacts completely according to 2Mg + O → 2MgO. What mass of magnesium oxide is formed? (Relative masses: magnesium 24, magnesium oxide 40.)
Answer and explanation
Correct answer: C. 20 g
- Step 1: Moles of magnesium mol.
- Step 2: From the equation, 1 mol of magnesium gives 1 mol of magnesium oxide, so moles of magnesium oxide mol.
- Step 3: Mass g.
Answer
20 g.
Why not the others: 12 g: it assumes mass is conserved between reactant and product alone. 40 g: it doubles the correct value.
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