Given 50 ml of concentrated nitric acid.The density of the concentrated acid is 1.42 g/ml and is 70% HNO3 by wt. Calc. the molality of the conc. acid.
density 1.42 g/mL. Then 1000 mL has a mass of 1.42 g/mL x 1000 = 1420 grams
That is 70% HNO3 so g HNO3 is
1420 x 0.70 = about 994 g. The rest of it is water.
g H2O = 1420-994 = about 426 g = 0.426 kg.
mol HNO3 = 994/molar mass HNO3.
m = mols HNO3/kg solvent.