. Jack Daniels Tennessee whiskey is 40.00% ethanol by volume. However, % alcohol by mass is quite different from % by volume. The molality of ethanol in an aqueous solution that is 40.00 % ethanol by volume is 10.88 molal.

Question

A) Find the % ethanol by MASS, based on the molality. The MM of ethanol, C2H5OH is 46 g.
B. Find the mole fraction of alcohol in the 10.88 molal ethanol solution.
C. The solution has a density of 0.948 g/mL. Find the molarity of the solution.

Answer 1

For A.
Assume you have enough solution to contain 10.88 moles ethanol. Therefore, you will have 1 kg water (1,000 g).
10.88 moles x (46 g/mol) = 500.48 grams ethanol.
Total mass of the solution is 1000 g + 500.48 = 1500.48 grams.
% ethanol = (mass ethanol/mass soln)*100
% ethanol = (500.48/1500.48)*100 = 33.35%.

For B, take enough sample to have 10.88 moles ethanol. That will give you 1,000 g H2O. Convert g H2O to moles and calculate mole fraction of each.

For C. I would use the mass percent and the density to calculate molarity.

Post your work if you get stuck.