A solution that contains 55.0 g of ascorbic acid (Vitamin C) in 250. g of water freezes at −2.34°C. Calculate the molar mass (in units of g/mol) of the ascorbic acid. Kf of water is 1.86°C/m.

Answer 1

From the amount of freezing point lowering and the Kf value, you can calculate the molality of the solution.
It's called Ebbing's formula. See
http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/meltpt.html

It tells us the solution is 1.25 molal. Therefore 250 ml and should have 0.313 moles of ascorbic acid.

If 0.313 moles is 55 g, the molar mass is 55/0.313 = 176.

The correct value is 176.12

http://en.wikipedia.org/wiki/Ascorbic_acid