Quick question

[kettles]

A quantitative analysis was carried out to find the percentage of phosphorous in a popular washing powder. (Phosphorous in the form of sodium tripolyphosphate is added as a 'builder' whose purpose is to remove calcium ions from the water). The phosphorus was precipitated as Mg2P2O7.

The results of washing powder= 5.02g
Mass of Mg2P2O7= 0.3023

What percentage of phosphorus was in the washing powder?

[illuminati]

M(Mg2P2O7) = 222.55g/mol
n(Mg2P2O7) = 0.3023/222.55 = 0.00136mol
n(P) = 0.00136 x 2 = 0.00272 (mole ratios)
m(P) = 0.00272 x 31 = 0.084g
%P = 0.084/5.02 x 100 = 1.68% w/w