Question

# ASAP! PLZ I need all answers for pre lab question in Molecular Weight Determination by Freezing...

ASAP! PLZ I need all answers for pre lab question in Molecular Weight Determination by Freezing Point Depression

Prelab questions:

(PL1) What is the molar mass of X (i=1) if 50.00g of water containing 2.50g of X has a freezing point of -11.5C?

(PL2) Using information from PL5, recalculate the molar mass of X if i=2.

(PL4) How is melting point different than freezing point?

(PL5) List the following in the increasing melting points. Pure water, 1.0M sugar water, 1.0M salt water.

PL1

MW if

dTf = -Kf * m * i

m = mol/kg solvent = (mass/MW) / kg solvent

then

dTf = -Kf*( (mass/MW) / kg solvent) * i

-11.5 = -1.86*(2.5/MW) / (50/1000) * 1

MW = -1.86*2.5 / ((50/1000) * 1) / -11.5 = 8.08695 g/mol

PL2

for i = 2

MW = -1.86*2.5*2 / ((50/1000) ) / -11.5 = 16.1739 g/mol

PL3

there is an increase due to the dissociation factor "i" of vant Hoff

PL4

melting --> solid to liquid, interactions are lower

freezing --> liquid to solid, interactions are stronger

PL5

Pure water < 1 M sugar (i = 1) < 1M Salt (i= 2)

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