Question

The chemical equation below shows the combustion of propane (C3H8).

C3H8 + 5O2 Right arrow. 3CO2 + 4H2O

The molar mass of oxygen gas (O2) is 32.00 g/mol. The molar mass of C3H8 is 44.1 g/mol. What mass of O2, in grams, is required to completely react with 0.025 g C3H8?
0.018 grams
0.034 grams
0.045 grams
0.091 grams

Answer 1

Moles C3H8 = 0.025 g / 44.1 g·mol−1 = 5.662×10−4 mol.
Moles O2 needed = 5 × 5.662×10−4 = 2.831×10−3 mol.
Mass O2 = 2.831×10−3 mol × 32.00 g·mol−1 = 0.0906 g ≈ 0.091 g.

Answer: 0.091 grams.