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When butane (C₄H₁₀) combusts completely, it forms CO₂ and H₂O. Write the balanced chemical equation and calculate the mass of CO₂ produced when 5.0 g of butane is burnt in excess oxygen.

medium 2 marks Class 10 · Science · Carbon and its Compounds
Answer
15.1 g of CO₂

The correct answer is 15.1 g of CO₂ — Mass of CO₂ = 0.344 mol × 44.01 g mol⁻¹ = 15.14 g, which is 15.1 g to three significant figures.

Step-by-step solution

  1. Write the balanced equation for complete combustion of butane: C₄H₁₀ + 13/2 O₂ → 4 CO₂ + 5 H₂O.
  2. Calculate the molar mass of butane: (4 × 12.01) + (10 × 1.008) = 58.12 g mol⁻¹.
  3. Find moles of butane used: 5.0 g ÷ 58.12 g mol⁻¹ = 0.0860 mol.
  4. From the balanced equation, 1 mol butane produces 4 mol CO₂, so moles of CO₂ = 0.0860 × 4 = 0.344 mol.
  5. Molar mass of CO₂ = (12.01) + (2 × 16.00) = 44.01 g mol⁻¹.
  6. Mass of CO₂ = 0.344 mol × 44.01 g mol⁻¹ = 15.14 g, which is 15.1 g to three significant figures.
Common mistake: Using the coefficient 2 for CO₂ instead of 4, leading to a lower calculated mass.

Concept tested: Combustion of alkanes

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