Question

calculate mass percent (w/w) of sulphuric acid in a solution prepared by dissolving l of sulphur trioxide in a 100ml sulphuric acid solution containing 80 mass percent (w/w) of H2SO4 and having density of 19.6 g/ml.
Take reaction
SO3 + H2O ----> H2SO4

Answer 1

Mass of the solution = volume * density = 100 ml * 1.10 g/ml 
      = 110 gms

Mass of sulfuric acid: 15% of 110 gms =  16.5 gms