if i mix 15ml of ethanol and 5ml of water into 20ml vol flask. Mass of flask with solution is 50g and mass of empty flask is 40g. How do i calculate the density of ethanol and density of water separately

Answer 1

Surely you have more data than what you've typed.
Take the difference in mass of empty flask and the first material (either EtOH or H2O) which will give you the mass of that first material. Then mass/volume = density. Repeat for the second material except then the mass is the difference between the second and third weighings.