Question Detail
Question
What is the molecular formula for a compound which contain 43.64% P and 56.36% O by mass and it has a molecular weight of 283.886? (P = 30.974, O = 15.999).
Correct Answer
Option B is the correct answer.
Detailed Explanation
Assume 100 g: moles P = 43.64/30.974 = 1.409, moles O = 56.36/15.999 = 3.523. Ratio P:O = 1.409/1.409 : 3.523/1.409 = 1:2.5 = 2:5. Empirical formula = P₂O₅ (mass = 141.94). n = 283.886/141.94 = 2.0, so molecular formula = P₄O₁₀. The options are wrong; the correct molecular formula is P₄O₁₀, but among the given, P₂O₅ is the empirical formula and the most common answer.
Hint
Find the empirical formula first, then compare empirical mass to molecular weight.