Calculating percent by mass

Question

Commercial aqueous nitric acid (HNO3) has a density of 1.42 g/mL and is 16 M. Calculate the percent HNO2 by mass in the solution.

Answer 1

find the moles of HNO3 in one litre:

@ 16 Molar.... there are 16 moles of HNO3

find the mass of HNO3 in that litre:

16 moles @ 63.012 g/mol = 1008.19 grams of HNO3

find the mass of the one litre:

1000ml @ 1.42g/ml = 1420 grams total

find the % mass:

1008 g HNO3 / 1420 g total (100) = 71.00 %

your answer is (2 sigfigs): 71 % HNO3 by mass