college chemistry 1

Question

Use dimensional analysis (e.g. percent composition) to convert 0.156 grams of phosphorus to grams of P₂O₅. (3 sig figs)

Answer 1

molar mass P2O5 = 141.94 g/mol

atomic mass P = 30.97 g/mol

Dimensional analysis:

0.156 g P x 1 mol P / 30.97 g P x 1 mol P2O5 / 2 mol P x 141.94 g P2O5 / mol P2O5 = 0.357 g P₂O₅

Check:

% P in P₂O₅ = 30.97 x 2 / 141.94 = 43.64%

If we have 0.357 g P₂O₅, the mass of P would be 0.357 g x 0.4364 = 0.156 g P which agrees with the value given in the problem.