Exploring the Anomalous i Value in Freezing Point Depression of KCl Solutions

In summary, the conversation discusses a question about the freezing point depression lab and the discrepancy between the experimental and theoretical values of "i" for KCl. The participants suggest looking into the van't hoff factor and possible causes for the difference, such as experimental error or math. They also mention the possibility of adding too much KCl or supercooling affecting the results.
  • #1
ada15
24
0
Hi Guys,

I have a question and its regarding to the freezing point depression lab ... I did an experiment where I had to find an "i" value for KCl. I'm getting 2.4 for "i" ... but the theoratical value is 2.

I was just wondering why expriment value os higher than the theortical value ? what would be the reason behind this?

Also, is there any website where I can find out that how the freezing point dpression graph look like for KCl?

Thanks
 
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  • #2
ada15 said:
I have a question and its regarding to the freezing point depression lab ... I did an experiment where I had to find an "i" value for KCl. I'm getting 2.4 for "i" ... but the theoratical value is 2.

I was just wondering why expriment value os higher than the theortical value ? what would be the reason behind this?

What's 'i'? The van't hoff factor?

Look into your book for the physical significance of the van't hoff factor and the answer should be obvious
 
  • #3
siddharth said:
What's 'i'? The van't hoff factor?

Look into your book for the physical significance of the van't hoff factor and the answer should be obvious

Perhaps I am missing something, but I think it should be just 2...

Experimental error? Math?



 
  • #4
Borek said:
Perhaps I am missing something, but I think it should be just 2...

Experimental error? Math?

Borek
-- \

Yep.

I was saying that if ada15 read up on the van't hoff factor, he/she would immediately know that theoretically it can't exceed 2 and therefore must be an experimental error or math.
 
  • #5
I remember getting a value of "i" that was much further away from the theoretical value, however, it was calculated from the equilibrium constant for an acid. What may have happened in your case is that you may have added an excessive amount of KCl. Another thing is that supercooling may have resulted in a decreased freezing point value...this was the case for our solution, the NaCl employed as an 'ice bath' to freeze the experimental solution had a graph of temperature versus time that showed an initial dip in the temperature and then rose to the 'real' freezing point temperature.
 

1. What is the purpose of a freezing point depression lab?

The purpose of a freezing point depression lab is to study the effect of adding a nonvolatile solute on the freezing point of a solvent. This allows scientists to understand the colligative properties of solutions and how they differ from pure substances.

2. How is the freezing point of a solution different from that of a pure solvent?

The freezing point of a solution is lower than that of a pure solvent due to the presence of a nonvolatile solute. This is because the solute molecules disrupt the crystal lattice structure of the solvent, making it more difficult for the solvent molecules to arrange themselves into a solid state.

3. What factors affect the extent of freezing point depression?

The extent of freezing point depression is affected by the concentration of the solute, the number of particles formed by the solute, and the nature of the solute and solvent. Stronger solutes and solvents tend to have a greater effect on the freezing point depression.

4. How is freezing point depression used in real-world applications?

Freezing point depression is used in various industries, such as food preservation, antifreeze production, and pharmaceuticals. It is also used in research to determine the molecular weight of unknown substances and to study the behavior of solutions under different conditions.

5. What are the potential sources of error in a freezing point depression lab?

Potential sources of error in a freezing point depression lab include inaccurate measurement of solute or solvent amounts, impurities in the solute or solvent, and temperature fluctuations during the experiment. It is important to control these variables carefully to obtain accurate results.

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