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).

Molarity = No of moles/Volume

Moles of Ethanol = 0.04 Mol

Moles of Water = 1-0.04 = 0.96

Mass of water = 0.96*18 = 17.3

Mass of ethanol = 0.04*46 = 1.84g

Therefore Total mass of the solution = 17.3 + 1.84 = 19.1g

Density = 1g/mL (Assumed)

Density = mass/volume so volume = mass/density

= 19.1/1 = 19.1mL = 0.0191L

hence Molarity = 0.04/0.0191

= 2.1M

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