Concentration of ethanol as a mass percent.

Question

Cask wine is available in a range of alcohol concentrations. Hardy's cask wine chardonnay contains 13.0% ethanol by volume. Calculate the concentration of ethanol as a mass percent. The density of ethanol (C₂H₅OH) is 0.789 g/cm³ and the density of the cask wine is 0.9784 g/cm³

Answer 1

mass % (m/v) is defined as grams of solute per 100 mls of solution.

% by volume is defined as mls of solute per 100 mls solution.

13.0% ethanol (by volume) = 13.0 ml ethanol / 100 mls solution

Since ethanol has a density of 0.9784 g / ml, we can determine how many grams 13.0% is...

13.0 ml ethanol x 0.9784 g / ml = 12.72 g ethanol in the 100 ml of solution

Ethanol (mass %) = 12.72% (i.e. 12.72 g per 100 mls of solution)