Question

a 1.000g sample of red phosphorus powder was burned in air and.reacted with oxygen gas to give 2.291g of phosphorus oxide. calculate the empirical formula andmolecular formula of phosphorus oxide give the molar mass is approximately 282g/mol?

Answer 1

The answers are: P₂O₅ (empirical formula) and P₄O₁₀ (molecular formula). See solution below:

Mass of P = 1.000 g

Mass of O = mass of phosphorus oxide - mass of P

= 2.291 - 1.000 = 1.291 g

Since moles = mass/molar mass

Moles of P : O = 1.000/30.974 : 1.291/15.999

= 0.03229 : 0.08069

= 2 : 5

Empirical formula is P₂O₅

Let the molecular formula be P_2aO_5a

Molar mass = 30.974 x 2a + 15.999 x 5a = 282

141.943a = 282 => a = 2

Molecular formula is P₄O₁₀