o
M2 can be determined by the equation o
The values of Kf and Kb can be determined from the following relations.
R = gas constant
M1 = molar mass of the solvent
Δfus H = enthalpies for the fusion of the solvent.
Δvap H = enthalpies for the vaporization of the solvent.
Calculate the mass of ascorbic acid( Vitamin C, C6H8O6) to be dissolved in 75 g of acetic acid to lower its melting point by 1.5 ° C.
Kf = 3.9 K kg mol-1.
Sol. Mass of acetic acid, w1 = 75 g Molar mass of ascorbic acid( C6H8O6),
M2 = 6 × 12 + 8 × 1 + 6 × 16 = 176 g mol- 1
Lowering of melting point, ΔTf = 1.5 K
=( 1.5 x 176 x 75) /( 3.9 x 1000) = 5.08 g( approx)
Hence, 5.08 g of ascorbic acid is needed to be dissolved.