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November 23, 2014

Homework Help: chemistry, freezing point depression

Posted by Sev on Friday, February 6, 2009 at 3:36pm.

Hey guys I did a lab and I have to answer the questions relating to the lab. I did question 1 & 2, can someone check if they are correct, and question 3 I don't know how to do it.

1. Calculation to Determine the molecular weight of unknown substance

Mass of unknown used: 2.0 g
Mass of water used: 50.0 g (0.05kg)
Kf = 1.86C kg/mole
Experimentally determined freezing point of unknown: -1C

Solution = delta Tf/-Kf
= -1C/-1.86C kg/mole
= 0.538 m (molality)

Molar mass = 2g / 0.05 kg * 0.538 m
= 74.4 g/mol

2. Calculations to determine i for KCl solution:

Kf = 1.86C kg/mole
Experimentally determined freezing point of KCl: -1C
m KCl (given): 0.1 m (molality)

Solution: i = measured delta Tf/ expected delta Tf
= -1C /-1.86C kg/mole * 0.1m KCl
i = 5.376

3. Explain why i has this value = ??

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