The equation for the burning of octane is:

2C₈H₁₈ + 25O₂ ⟶ 16CO₂ + 18H₂O

(i) How many moles of carbon dioxide are produced when one mole of octane burns?

(ii) What volume at S.T.P. 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?

$\begin{matrix} 2\text{C}_8\text{H}_{18} & + &25\text{O}$2 & \longrightarrow & 16\text{CO}2 & + & 18\text{H}2\text{O} \ 2\text{ Vol.}&& 25\text{ Vol.} && 16\text{ Vol.}&& 18\text{ Vol.} \ &&&&16[12 + 2(16)] \ &&&&16[12 + 32] \ &&&&16[44] = 704 \text{g} \ \end{matrix}

(i) 2 moles of octane produces 16 moles of CO₂

∴ 1 mole octane produces $\dfrac{16}{2}$ x 1

= 8 moles of CO₂

(ii) 1 mole CO₂ occupies volume = 22.4 L

As 2 moles of octane produces 8 moles of carbon dioxide which will occupy volume $\dfrac{22.4}{1}$ x 8

= 179.2 dm³ of CO₂

(iii) 1 mole CO₂ has mass = 44 g

∴ 16 moles will have mass $\dfrac{44}{1}$ x 16

= 704 g of CO₂

(iv) Molecular formula is C₈H₁₈

∴ Ratio of C and H is 8 : 18

Simple ratio is 4 : 9

Hence, empirical formula = C₄H₉