In a closed vessel, 1 g of magnesium is burnt with 0.5 g of oxygen gas. Which reactant remains in excess? Find the quantity of excess reactant. [Mg = 24, O = 16]
WBBSE
Class X
Physical Science
Chemical Calculations
03 Mark
2025
Mass of Mg = 1 g
Mass of Oâ‚‚ = 0.5 g
Balanced Chemical Equation:
2Mg + O₂ → 2MgO
Molar mass of Mg = 24 g/mol
Molar mass of Oâ‚‚ = 32 g/mol
From the balanced equation,
48 g of Mg reacts with 32 g of Oâ‚‚.
Therefore, Mg required to react with 0.5 g of Oâ‚‚
= \frac{48 \times 0.5}{32}
= 0.75 g
Available Mg = 1 g
Excess Mg = 1 − 0.75 = 0.25 g
Hence, magnesium remains in excess and the excess quantity is 0.25 g.
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