Answer:
Mass = 87.952 g
Explanation:
Given data:
Mass of phosphorus = 20.0 g
Theoretical yield of P₂O₃ = ?
Solution:
Chemical equation:
P₄ + 3O₂  →  2P₂O₃
Number of moles of phosphorus:
Number of moles = mass/ molar mass
Number of moles = 20.0 g / 123.9 g/mol
Number of moles = 0.2 mol
Now we will compare the moles of phosphorus with P₂O₃.
             P₄     :      P₂O₃
             1      :      2
             0.2     :     2/1×0.2 = 0.4 mol
Theoretical yield:
Mass = number of moles × molar mass
Mass = 0.4 mol  × 219.88 g/mol
Mass = 87.952 g