Calculate the mass of air required to burn 20 grams of sulfur, assume that the mass fraction of oxygen in the air is 23.1%.

Given:
n (S) – 20g
w (O2) -23.1%
Find: m (air) -?
Let’s make the equation:
S + O2 = SO2
sulfur and oxygen 1 mole each
M (S) = 32 g / mol
M (O2) = 32 g / mol (16 * 2)
m (O2) = 20g
n (S) = 20g / 32g / mol = 0.625 mol
x = 20 * 32/32 = 20g (oxygen)
20g-23.1% x-100%
x = 20 * 100 / 23.1 = 86.6 g
Answer: m (air) = 86.6g.