The amount of carbon dioxide evolved upon complete combustion of 116 g of n-butane is: (Atomic masses: H =1, C =12, O =16)

Solution & Explanation

Concept: stoichiometry via the balanced combustion equation and mole ratios. Combustion of n-butane: C₄H₁₀ + (13/2)O₂ → 4CO₂ + 5H₂O. Molar mass of C₄H₁₀ = 4(12) + 10(1) = 48 + 10 = 58 g mol⁻¹. Moles of butane = 116 / 58 = 2 mol. From the equation, 1 mol butane gives 4 mol CO₂, so 2 mol butane gives: moles CO₂ = 2 × 4 = 8 mol. Mass of CO₂ (molar mass 44 g mol⁻¹) = 8 × 44 = 352 g. Hence 352 g of CO₂ is evolved — answer (A). Trap: forgetting the 4:1 CO₂-to-butane ratio (each butane has 4 carbons) would give a wrong, smaller answer such as 88 g.