1. when .357 grams of an unkown compound is dissolved in 17.0 grams of benzene,
ID: 827073 • Letter: 1
Question
1. when .357 grams of an unkown compound is dissolved in 17.0 grams of benzene, the freezing point of the solution is depressed by 0.250 degrees C. what is the molar mass of the unkown compound?
2.Glycerol, C3H8O3, is essentially a nonvolatile liquid that is very soluble in water. A solution is made by dissolving 68 g of glycerol in 375 g of water. Calculate the freezing point of the solution.
3. The formula and the molecular weight of an unkown hydrocarbon compound are to be determined by elemental analysis and the freezing point depression method.
Explanation / Answer
a) For freezing point depression problems you use molal solution
A molal solution is defined as : mol solute per 1kg solvent = or 1000g solvent
You have 0.357g solute in 17g benzene - that is 21g solute per kg benzene
Kf for benzene is 5.12
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