What mass of phosphorus must react with 32.5 g of oxygen?

Question

2P + 5O2 --> 2P2O5

Answer 1

4P + 5O₂ --> 2P₂O₅ .. balanced equation

If you have 32.5 g of O₂, how many moles is this?

32.5 g x 1 mol O₂ / 32 g = 1.016 moles of O2 present

How many moles of P are needed to react with 1.016 moles of O₂?

1.016 mols O₂ x 4 mols P / 5 mols O₂ = 0.8125 moles of P needed

Convert 0.8125 moles P to grams of P using the atomic mass of P (30.97 g/mol):

0.8125 mols P x 30.97 g / mole = 25.2 g P needed (3 significant figures)

Answer 2

Your reaction should be 4P or you could use the allotrope P₄ in the reaction statement

32.5 g O₂(1 mole/32.00 g O₂)(4 mole P/5 mole O₂)(30.97g/mole P) = g P

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