Find the m of phosphorus in a 250ml solution. This phosphorus comes from a 2.75mg/L sample of phosphate.?

The percent m of phosphorous in phosphate is 37.61% (P MW=30.973, PO4- MW=94.973, therefore 30.973/94.973 x 100%= 37.61%). The next part we have to deal with is the amount, in mg of PO4- in 250mL. This equates to 2.75mg/L x .250 L =0.68mg. Thus the amount of elemental phosphorous in this 250mL solution would simply be 0.68mg x .30973, more correctly rounded to 2 significant figures, i.e 0.68 x .31= 0.21mg.