Calculate the amount of substance and mass of phosphorus required to obtain 71 g of phosphorus (V) oxide.

Phosphorus (V) oxide can be obtained by burning phosphorus in oxygen. The equation for this reaction looks like this:

4 P + 5 O2 = 2 P2O5

It can be seen from the reaction equation that the ratio of the amount of phosphorus substance to the amount of its oxide substance is 4/2 or 2/1. In other words, the amount of phosphorus substance is twice as large as the amount of phosphorus oxide substance. Therefore, to solve the problem, we need to first calculate the amount of phosphoric anhydride substance P2O5, then we will find the amount of phosphorus substance and easily calculate its mass.

Molar mass P2O5 = 142 g / mol; molar mass of phosphorus = 31 g / mol

N (P2O5) = 71/142 = 0.5 mol of phosphorus (V) oxide

N (P) = 0.5 * 2 = 1 mol of phosphorus

m (P) = 1 * 31 = 31 g.

Answer: 1 mol, 31 g of phosphorus