Question

The equation for the burning of octane is:
2C₈H₁₈ + 25O₂ $\stackrel{}{\to }$ 16CO₂ + 18H₂O
(i) How many moles of carbon dioxide are produced when one mole of octane burns?
(ii) What volume, at STP, is occupied by the number of moles determined in (i)?
(iii) If the relative molecular mass of carbon dioxide is 44, what is the mass of carbon dioxide produced by burning two moles of octane?
(iv) What is the empirical formula of octane?

Answer 1

(i) According to the balanced chemical equation, one mole of octane will produce eight moles of carbon dioxide.

(ii) At STP, volume occupied by one mole of gaseous carbon dioxide is 22.4 L.
Volume occupied by 8 moles of carbon dioxide at STP = (22.4 $\times$ 8) L = 179.2 L

(iii) When two moles of octane are burnt, 16 moles of carbon dioxide is formed.
Mass of 16 moles of carbon dioxide = $\mathrm{Number}\mathrm{of}\mathrm{moles}\times \mathrm{Relative}\mathrm{molecular}\mathrm{mass}=\left(16\times 44\right)\mathrm{g}=704\mathrm{g}$

(iv) Empirical formula of a compound is the simplest ratio of its constituent atoms. Hence, empirical formula of octane is C₄H₉.