A solution is made using 150.0 mL of ethanol (density 0.7892 g/mL) and 350.0 mL of water (density 1.000 g/mL). What is the molality ethanol in water?

Answer 1

Molality = moles of solute / kg solvent

solute = ethanol (C₂H₅OH; molar mass 46.07 g/mol). Solvent = H₂O

moles solute = 150.0 ml ethanol x 0.7892 g / 1 ml = 118.38 g x 1 mol / 46.07 g = 2.5696 mols ethanol

kg water = 350.0 ml x 1 g / ml x 1 kg / 1000 g = 0.3500 kg

Molality of ethanol = 2.5696 mols / 0.3500 kg = 7.342 m