Question

What is the freezing point of radiator fluid prepared by mixing 1.00L of ethylene glycol (HOCH₂CH₂OH, density = 1.114g/mL) with 1.00L of water (density 1.000 g/mL)? The freezing point depression constant of water, K_f is 1.86^oC/m [NOTE: water is the solvent in this solution]

Answer 1

Depression in freezing point is related to the molality of the solution , therefore molality of the solution with

respect to ethylene glycol = moles of ethylene glycol / mass of water in kilograms

moles of ethylene glycol = [ (1000 x 1.114) / 62 ] = 1114 / 62 = 17.97 mole

mass of water in Kg = (1000g. x 1.000 ) = 1000gms ,or = 1Kg

hence , molality (m) of ethylene glycol = 17.97 mol / 1 kg. = 17.97 mol kg^-1

Therefore, freezing point depression T_f = K_f . m

.................................................................... = 1.86 x 17.97

.................................................................... =33.42 K

Freezing point of aqueous solution = (273.15 - 33.42)

....................................................... = 239.73 K

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