Answer to Question #121790 in General Chemistry for Victoria

Question

Calculate the volume of oxygen required to burn 40ml of octane (C8H18) completely. The combustion of octane is ? (2C8H18+25O2 ➡️ 16Co2+18H2O

Answer 1

2C₈H₁₈ + 25O₂ = 16CO₂ + 18H₂O

Octane's density is 0.703 g cm⁻³

40 mL of it weights:

40 x 0.703 = 28.12 g

M (octane) = 114.23 g/mol

n = 28.12 / 114.23 = 0.246 mol

The mole ratio of octane and oxygen gives us: 25/2 x 0.246 = 3.077 mol of O₂

At STP the molar volume of a gas (Standard Temperature and Pressure) is equal to 22.4 L 

3.077 x 22.4 = 68.93 L of O₂