chemistry
posted by Lahna .
Calculate the molarity of a phosphoric acid(H3PO3)solution that is 84% by mass phosphoric acid and has a density of 1.87g/mL.?

1.87 g/mL. mass of 1000 mL =
1.87g/mL x 1000 mL = 1870 grams.
How much of that is H3PO4? 84%, so
1870 x 0.84 = grams H3PO4 = 1571g
How many moles is that?
1571/molar mass H3PO4 about 16 moles.
16 moles/L soln = about 16 M.
I have rounded some of the numbers above; therefore, you need to go through and do it more accurately. 
How many grams of water and how many grams of 85 wt% phosphoric acid would be needed to make 100 grams of 37 wt% phosphoric acid solution?