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

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.

To calculate the density of ethanol and water separately, you need to use the formula:

Density = Mass / Volume.

Let's calculate the volume of the ethanol and water separately first.

The total volume of the mixture is 20 ml, consisting of 15 ml of ethanol and 5 ml of water.

To calculate the density of ethanol:

1. Calculate the mass of ethanol in the mixture.
Mass of ethanol = Mass of flask with solution - Mass of empty flask
Mass of ethanol = 50g - 40g = 10g

2. Calculate the density of ethanol.
Density of ethanol = Mass of ethanol / Volume of ethanol
Volume of ethanol = 15 ml
Density of ethanol = 10g / 15 ml = 0.67 g/ml

To calculate the density of water:

1. Calculate the mass of water in the mixture.
Mass of water = Mass of flask with solution - Mass of empty flask
Mass of water = 50g - 40g = 10g

2. Calculate the density of water.
Density of water = Mass of water / Volume of water
Volume of water = 5 ml
Density of water = 10g / 5 ml = 2 g/ml

Therefore, the density of ethanol is 0.67 g/ml, and the density of water is 2 g/ml.