Wednesday
October 1, 2014

Homework Help: Chemistry please help

Posted by Saira on Wednesday, May 27, 2009 at 9:15pm.

Hey guys I did a lab and I have to answer the questions relating to the lab. I did question can someone please check if these are accurate

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:

FOR PART 2 I AM NOT SURE WHAT IS THE RIGHT METHOD OF DOING IT, I DID IT TWO WAYS CAN SOMEONE PLEASE CHECK, WHICH IS THE RIGHT ONE.


Kf = 1.86C kg/mole
Experimentally determined freezing point of KCl: -5.00
m KCl (given): 0.1 m (molality)

1. . Solution: i
= -5.00C /(1.86C kg/mole)(0.1)
i = 26.88
or

2. -5.00C /-1.86C kg/mole * 0.1m KCl
i = 0.2688

So is i 0.2688 or would it be 26.88

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