Question

Calculate the molarity of a solution of ethanol in water in which the mole fraction of

ethanol is 0.040(assume the density of water to be one).

Answer 1

Moles of ethanol = 0.04 mol

Moles of water = 1-0.04 = 0.96 mol

Mass of water = 0.96 mol x 18 g/mol = 17.3 g

Mass of ethanol = 0.04 mol x 46 g/mol = 1.84 g

Mass of the solution = 17.3 g + 1.84 g = 19.1 g

Assuming density of solution to be 1 g/ml,

Volume of solution = mass/density = 19.1/1 = 19.1 ml = 0.0191 L

Molarity is the number of moles of solute present in 1L of solution,

Molarity = 0.040/0.0191 = 2.1 M