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A solution of ethanol, and water freezsz at -22.5'C. What is the percentage by mass of...

A solution of ethanol, and water freezsz at -22.5'C. What is the percentage by mass of ethanol in the solution? The answer is 35.8% enthanol, but I can't get the answer. Please help me

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Answer #1

Freezing point depression =kf*m*i

i= Van't Hoff facotr =1 for water

kf= freezing point depression constant =1.86 deg.c/m and m= molality of ethanol

22.5= 1.86*m

22.5/1.86 = molality of ethanol=12.1 moles of ethanol pe kg of water

Basis : 1 kg water. it contain 12.1 moles of ethanol, molecular weight of ethanol (C2H5OH)= 46

mass of ethanol= 12.1*46=556.6 gm

total mass = mass of water (1000 gms)+ mass of ethanol (556.6)= 1556.6 gm

Mass % ethanol =100*556.6/1556.6=35.7%

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