Calculate the mass fraction of phosphorus in phosphorus (III) oxide and phosphorus (V) oxide.

Given: oxides P2O3 and P2O5. Find: ω1 (P) – ?, ω2 (P) -?
Decision.
1. Mass fraction of phosphorus in P2O3 oxide.
Mr (P2O3) = 2 • Ar (P) + 3 • Ar (O) = 2 • 31 + 3 • 16 = 110
ω1 (P) = (2 • Ar (P) / Mr (P2O3)) • 100% = (2 • 31: 110) • 100% = 56.36%
2. Mass fraction of phosphorus in oxide P2O5.
Mr (P2O5) = 2 • Ar (P) + 5 • Ar (O) = 2 • 31 + 5 • 16 = 142
ω2 (P) = (2 • Ar (P) / Mr (P2O5)) • 100% = (2 • 31: 142) • 100% = 43.66%
Answer: in P2O3 oxide, the mass fraction of phosphorus is higher than in P2O5 oxide.

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