Find the mass of burned phosphorus if 22.27 grams of P2O5 is formed.

First, we write down the equation of reactions.
4P + 5O2 = 2P2O5.
First, we find the amount of phosphorus oxide substance. We use the following formula.
n = m / M.
Find the molar mass.
M (P2O5) = 30 × 2 + 5 × 16 = 60 + 80 = 140 g / mol.
n = 22.27 g / 140 g / mol = 0.159 mol.
Further, according to the reaction equation, we find the amount of moles of phosphorus.
X mol P – 0.159 mol P2O5.
4 mol Р – 2 mol Р2О5.
X = 4 × 0.159 ÷ 2 = 0.318 mol.
Next, we find the mass of phosphorus.
M (P) = 30 g / mol.
m = n × M = 0.318 mol × 30 g / mol = 9.55 g.
This means that the mass of burned phosphorus is 9.55 grams.
Answer: m (P) = 9.55 g.