What is the mole fraction of water in 200 g of 95% (by mass) ethanol, C2H5OH?

Answer 1

If the solution is 95% by weight, that means that in 100 grams of solution you have 5 grams of water and 95 grams of ethanol.

Convert each of these masses to moles by dividing each mass by the molar mass of the compound.

5 g/18 g/mol = 0.278 mol water
95 g / 46g/mol = 2.065 mol ethanol

Mole fraction water:
= mol water / total moles
= 0.278/ (0.278 + 2.065)
= 0.119

Answer 2

Mole Fraction

Answer 3

You need to first find the molecular weight of ethanol, which is (12*2)+(5*1)+(16*1)+(1*1)=46g/mol.

You also need the molecular weight of water, which is (2*1)+(16*1)=18g/mol.

You also need to know the mass of the different substances in the solution. The amount of ethanol is 200*0.95 and the amount of water is 200* 0.05. This will give you the amount in grams of each substance. You then need to convert to moles.

For ethanol this would be g ethanol * (1 mole ethanol/MW ethanol)
For water, g water * (1 mole water/MW water)

Sum these two numbers to get the total number of moles in the solution.

To get the mole fraction of water, divide the number of moles of water by the total number of moles in the solution.

Answer 4

Mole fraction is an intensive property so the 200 g is irrelevant.

Answer 5

mole fraction of a component = moles of component/total moles

Mwt of ethanol=46
mass of ethanol=0.95*200=190 g
Moles of ethanol=190/46=4.13

mwt of water=18
mass of water=200-190=10 g
moles of water=10/18=0.5556

total moles=4.685

Mole frac of water=0.5556/4.685
=0.1185

Answer 6

OK!

95% of 200 g = 190 g of ethanol

Assume that all of the remainder, or 10 g, is water.

Now, calculate the number of moles of each:

190 g * (mole ethanol/ 46 g) = 4.13 moles ethanol

10 g * (mole water)/ 18 g = 0.56 moles water

So, the mole fraction of water is:

moles water / (moles ethanol + moles water) =

0.56/(4.13 + 0.56) = 0.12

Done.