i) depression in freezing point ΔTf = 7.19 oC - (-0.98 oC) = 8.17 oC
ii) mass of solute = volume x density = 5 ml x 6.18 g/ml = 30.9 g
molar mass of unknown, M = ?
mass of solvent in Kg , W = 0.5 kg
molality = (w/M) x (1/W in kg)
= (30.9 g/M) x (1/0.5 kg)
= (30.9 /M) x (1/0.5) m
iii) ΔTf = kf x molality
8.17 ^{o}C = 9.8 ^{o}C m^{-1} x (30.9 /M) x (1/0.5) m
M = 74.1 g/mol
Hence,
Molar mass of unknown = 74.1 g/mol
The freezing point depression of a solution made by the addition of a nonionic unknown solute...
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