Freezing point depression error

In summary, the conversation discusses an experiment involving freezing point depression and calculated molar mass values that were larger than the actual values. It is questioned how the presence of solvent on the walls of the test tube may affect the results and calculations. It is determined that this presence would lead to an underestimation of the molality. The equation for the relationship between molality and molar mass is discussed, using the masses of the solvent and solute in the experiment.
  • #1
needchemhelp
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So we did an experiment of freezing point depression and my calculated molar mass values were larger than actual...
First, the freezing point of the pure solvent had to be determined and so if some of the solvent was on the walls of the test tube opposed to in the solution how would this affect results?
As far as I've gotten is that it would result in a greater actual molality than observed, but how would this then effect temperature change and molar mass?

hope this is enough, please help
 
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  • #2
To help you, we must first guess what your experiment involved (measure FP of pure solvent; add known mass of solute; measure FP of solution; use known FP depression constant to calculate molality; and from masses of solute and solvent calculate molar mass?). It would have helped if you had included these details in the opening post.

If the above guess is correct (please confirm whether they are), then, as you said, the real molality will be greater than the calculated molality, due to solvent on the walls. So, the calculation underestimates the molality.

M'(calc) =M(real) - dM (where dM >0)

How do you relate the molality to the molar mass? Write down the equation for that relationship. I imagine you used some fixed mass s of the solvent and dissolved some small mass m of the solute in it. If that's true, can you write down the equation relating M (the molality) to MM (the molar mass) using m and s?
 
  • #3


It is possible that the presence of solvent on the walls of the test tube could have affected the results of your experiment. This could have caused a higher actual molality than observed, which would result in a lower freezing point depression than expected. This could explain why your calculated molar mass values were larger than the actual values.

To address this issue, it is important to ensure that the test tube is completely clean and free of any excess solvent before conducting the experiment. This can be done by rinsing the test tube with a small amount of the solvent and then drying it thoroughly.

Additionally, it is important to make sure that the solution is well-mixed before taking measurements. This will help to ensure that the concentration of solute is consistent throughout the solution.

It is also possible that there were other sources of error in your experiment that could have contributed to the discrepancies in your results. It is important to carefully follow the experimental procedure and to take multiple measurements to reduce the impact of any individual errors.

In conclusion, the presence of solvent on the walls of the test tube could have affected your results in the freezing point depression experiment. It is important to take precautions to ensure that the test tube is clean and the solution is well-mixed in order to obtain accurate results. Additionally, it is important to consider other potential sources of error in your experiment.
 

Related to Freezing point depression error

1. What is freezing point depression error?

Freezing point depression error is a phenomenon in which the freezing point of a solution is lower than the expected value due to the presence of a solute.

2. What causes freezing point depression error?

Freezing point depression error is caused by the presence of a solute in a solution. The solute molecules disrupt the crystal formation of the solvent, resulting in a lower freezing point.

3. How does freezing point depression error affect experiments?

Freezing point depression error can affect experiments by causing inaccuracies in determining the concentration of a solution. It can also affect the properties and behavior of the solution, leading to unexpected results.

4. How can freezing point depression error be minimized?

Freezing point depression error can be minimized by using a highly pure solvent, accurately measuring the amount of solute added, and ensuring that the solution is well-mixed. Additionally, performing the experiment at a lower temperature can also reduce the effect of freezing point depression.

5. Are there any real-world applications of freezing point depression error?

Yes, freezing point depression is utilized in various applications such as antifreeze solutions for cars, salt on icy roads, and cryopreservation of biological samples. It can also be used to determine the molecular weight of unknown substances through colligative properties.

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