Question

At 25 degrees C, 50% mass ethanol/ water mixture has a density of 0.914 g/cm^3. If V H2O= 17.3 (cm^3)/ mol in the mixture, what is V EtOH?

Answer 1

Let the total volume of solution be 100 cm^3

total mass of solution = density x volume

                                   = 0.914 x 100

                                   = 91.4 g

half of this 45.7 g is water and 45.7 g is ethanol

let nA and nB be moles of water and ethanol, respectively

vA and vB be volume of water and ethanol, respectively

So total volume

V = nA.vA + nB.vB

100 = (45.7/18.02) x 17.3 + (45.7/46.07) x vB

So,

volume of ethanol in the mixture (vB) = 56.6 cm^3/mol