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Molar mass of compound

The freezing point of a solution having 4.8 g of a compound in 60 g of benzene is 4.48. Determine the molar mass of the compound (Kf = 5.1 Km-1) , (freezing point of  benzene = 5.5oC)              
(a) 100   (b) 200   (c) 300   (d) 400

Answer: (d) m = (Kf x 1000 x w)/W x ΔTf = (5.1 x 1000 x 4.80)/(60 x 1.02) = 400

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