Question

The density of an aqueous solution containing 10% of ethanol (C2H5OH) by mass is 0.984 g/ml.

A) Calculate the molality of this solution.

B) Calculate its molarity.

C) What volume of the solution would contain 0.125 mol of ethanol.

Answer 1

10% means 10 g EtOH/100 g solution which is 10 g EtOH/(10 g EtOH + 90 g water).

A. 10 g is how many moles? moles = grams/molar mass.
m = moles/kg solvent.
Substitute moles from above. kg solvent is 0.090 kg.

B. molarity = moles/L soln.
moles you have from above.
The 10% soln has a mass of 100 grams. Use the density to convert 100 g to volume (which will be in mL), then convert to L and divide moles/L to arrive at molarity.

C. M x L = 0.125. You have M, solve for L.

Answer 2

Thank you!