a sample of pure benzene was found to freeze at 5.48c. a solution made by dissol

Question

a sample of pure benzene was found to freeze at 5.48c. a solution made by dissolving 20 g of an unknown compound in 500 g of benzene was found to freeze at 3.77c. given that the molar freezing point constant of benzene is 5.12cm what is the molar mass of the unknown compound? a sample of pure benzene was found to freeze at 5.48c. a solution made by dissolving 20 g of an unknown compound in 500 g of benzene was found to freeze at 3.77c. given that the molar freezing point constant of benzene is 5.12cm what is the molar mass of the unknown compound?

Explanation / Answer

Tbenzene= 5.48oC T solution=3.77

Tf=3.77-5.48=-1.71

delta Tf=-Kf x m

Kf = freezing point depression constant,m= molarity

m=delta Tf / -Kf= -1.71/ -5.12=0.334m

amount of solute = 0.5Kg benzenex 0.334m=0.167msolute

molar mass of unknow compound = 20/0.167=119.760 g/mol

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