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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

Answer

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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