When 0.062 g of Red Phosphorous burns in the air it forms 0.142 g of Phosphorous Oxide. What is the empirical formula of Phosphorous Oxide?

Answer 1

The gram Atomic Mass of phosphorus is 30.9738, and that of oxygen is 15.9994. From the "Law of the Conservation of Mass", the amount of oxygen incorporated into the phosphorus oxide is 0.142 - 0.062 or 0.080 grams. The specified 0.062 grams of mass of phosphorus constitutes 0.062/30.973 or 2.00 X 10-3, to the (maximum possibly) justified number of significant digits, of Avogadro's Number of phosphorus atoms, and 0.080/15.9994 corresponds to 5.00 X 10-3 of Avogadro's Number of oxygen atoms. The ratio 5/2 does not reduce to any integral value; therefore, the empirical formula is P2O5.

Answer 2

The molar mass of red phosphorus is 31.0 g/mol and of phosphorus oxide is 91.0 g/mol. From the given masses, we find that 0.062 g of red phosphorus is equivalent to 0.002 moles and 0.142 g of phosphorus oxide is equivalent to 0.00156 moles. The empirical formula of phosphorus oxide is P2O5.