Phosphorus combustion reaction:
4P + 5O2 = 2P2O5.
From the reaction equation it follows that 4 mol of phosphorus enters the reaction with the formation of 2 mol of oxide, which means:
n (P) = 2 • n (P2O5).
Find the practical number of moles:
n (P2O5). = m / Mr = 22/142 = 0.15 mol.
n (P) = 2 * 0.15 = 0.3 mol.
Then the mass of phosphorus:
m (P) = n • Mr = 0.3 • 31 = 9.6 g.
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