MASINDE MULIRO UNIVERSITY OF SCIENCE AND TECHNOLOGY

Question

SCHOOL OF NATURAL SCIENCES
Department of Pure and Applied Chemistry
SCH 140: Physical Chemistry
CAT 2 18/01/2021
Instructions:
Each question has 5 marks
Due Date: Friday, 22nd January 2021 latest 5 pm
Submission through respective class reps

1. A crystalline white solid is a mixture of glucose (C6H12O6) and sucrose
(C12H22O11). Is it possible that a 10.00g sample of the solid dissolved in 100.0 g
H2O might have a freezing point of -1.25oC? Explain.

Answer 1

Assume two scenarios; i.e., the 10 g sample is 100% glucose or is 100% sucrose.
A. If 100% glucose then
mols glucose = grams/molar mass = 10.00/180 = 0.0555
molality = mols/kg solvent = 0.0555/0.100 = 0.555
dT = i*kf*m = 1*1.86*0.555 = 1.03 so freezing point is -1.03 so glucose won't do it.
B. If 100% sucrose. Since molar mass sucrose is higher than that of glucose (342 vs 180) then mols sucrose will be lower, molality will be lower, delta T will be lower and freezing point will be higher. You can confirm all of this--I didn't want to do the calculation.
So the answer to the problem is no, the freezing point cannot be as low as -1.25 C.

Answer 2

cocaine