Compound: Concentration: Measured deltaT
LiCl 6.00 g/kg 0.492 deg C
HCl 4.00 g/kg 0.389 deg C
NaCl 6.00 g/kg 0.356 deg C
Determine the value of the vant hoff factor for each salt for the experimentally measured delta T value. (kf=1.86)
I have tried to figure this out, but it is saying I'm wrong. I might be doing the math wrong. Can you help me?
dT = i*Kf*m
i = dT/(Kf*m)
dT = 0.492 for LiCl
Kf = 1.86 (I assume you are using this value or one given in class to use.
m = mols/kg solvent
mols = 6.00/molar mass LiCl
I get 1.869 for i which would round to 1.87.
If you post your work for one of the problems I will find your error for you.
I calculate the amount of kg, which is .00600 kg. Then I calculate the molality:
.14 mols/.00600kg = 23.3 m
23.3*1.86=43.338
.492/43.338=.0114
I don't know which step is incorrect.
The way I read the LiCl part of the problem, (LiCl) = 6.00 g/kg ; therefore, mols LiCl = 6.00 g/42.394 = 0.1415
m = 0.1415 mols/1 kg solvent.
i = 0.492/(0.1415*1.86) = 1.869 which I rounded to 1.87. Therefore, i isn't quite 2 as we would predict for two particles (Li^+ and Cl^-) but just less than that. Your error is in calling the solvent 0.006 kg; the problem says it is 1 kg (at least 6.00 g LiCl/kg says that to me). That means to me you would have 12.00 g/2 kg, 18.00 g/3 kg etc.
thank you! I figured that was the problem.
To determine the value of the van't Hoff factor (i), which represents the number of particles a compound dissociates into in a solution, you need to use the formula:
i = (Measured deltaT)/(Molal concentration * Vant Hoff factor constant)
Given the measurements you provided and the van't Hoff factor constant (kf = 1.86), let's calculate the value of i for each salt:
For LiCl:
- Measured deltaT = 0.492 °C
- Molal concentration = 6.00 g/kg (Note: 1 kg of water = 1 L of water by definition)
- Vant Hoff factor constant (kf) = 1.86
i (LiCl) = (0.492 °C) / (6.00 g/kg * 1.86)
Now, let's compute this value:
i (LiCl) = 0.492 °C / 11.16 g/kg
i (LiCl) ≈ 0.044
Similarly, for HCl:
- Measured deltaT = 0.389 °C
- Molal concentration = 4.00 g/kg
- kf = 1.86
i (HCl) = 0.389 °C / (4.00 g/kg * 1.86)
i (HCl) ≈ 0.052
Lastly, for NaCl:
- Measured deltaT = 0.356 °C
- Molal concentration = 6.00 g/kg
- kf = 1.86
i (NaCl) = 0.356 °C / (6.00 g/kg * 1.86)
i (NaCl) ≈ 0.032
Therefore, the van't Hoff factors for LiCl, HCl, and NaCl, respectively, are approximately 0.044, 0.052, and 0.032.