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Question
Calculate the mass of ascorbic acid (molecular mass = 176 g/mol) that should be dissolved in 155 g of acetic acid to cause a depression of the freezing point by 1.15 K. Assume that ascorbic acid does not dissociate or associate in the solution. (Kf for acetic acid = 3.9 K kg/mol)
Solution
Mass of acetic acid (ω1) = 155 gm
Molar mass of ascorbic acid = 176 g mol-1
Lowering melting point, ΔTf = 1.15 K
`Delta "T"_"f" = ("K"_"f" xx 1000 xx omega_2)/("M"_2 xx omega_1)`
`omega_2 = (1.15 xx 176 xx 155)/(3.9 xx 1000)`
`omega_2 = 8.044` gm
Hence, 8.044 g of ascorbic acid is needed to be dissolved.
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