Determining molar mass by freezing point depression lab

In summary, the conversation was about a student having trouble with a chemistry lab problem and asking for ideas. The problem involved calculating the molar mass of an unknown substance in a solution with known values for Kf, solution mass and temperature change. The relevant equations to solve the problem are the freezing point depression equation, molality equation, and the definition of molality which depends on the molar mass of the substance. The student was asked to use the template provided to organize their knowledge and find a solution to the problem on their own.
  • #1
kevin0788
6
0
Im doing my chemistry lab and ran into trouble with this problem. I am not even where to start or what formulas to use. Any ideas? Thanks.

Suppose that a student calculated Kf of biphenyl to be 81.2 C kg/mol. Calculate the molar mass of an unknown if a solution containing 1.64g of an unknown in 18.22 g of biphenyl froze at 39.9 C
 
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  • #2
What was freezing point depression? What was molality of unknown substance? What is molality definition and how does it depend on the molar mass of the substance?

Note: template provided is to help you organize your knowledge. Basically if you would think what to put into "relevant equation" section you would have to answer questions that I have just posted. So in the future don't ignore the template, put some effort into using it and you will find you know how to solve many questions by yourself.

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Related to Determining molar mass by freezing point depression lab

What is the purpose of the "Determining molar mass by freezing point depression lab"?

The purpose of this lab is to determine the molar mass of an unknown substance by measuring the freezing point depression caused by the addition of the substance to a known solvent.

What materials are needed for this lab?

The materials needed for this lab include a known solvent, an unknown substance, a thermometer, a beaker, a stirrer, and a hot plate.

What is the procedure for conducting this lab?

The procedure for this lab involves measuring the freezing point of the known solvent, adding a known amount of the unknown substance to the solvent, and then measuring the freezing point again. The difference between the two freezing points is used to calculate the molar mass of the unknown substance.

How does freezing point depression relate to molar mass?

Freezing point depression is a colligative property, meaning it is affected by the number of particles in a solution. The more particles present, the lower the freezing point. Molar mass is directly related to the number of particles in a solution, so by measuring the freezing point depression, we can calculate the molar mass of the unknown substance.

What are some potential sources of error in this lab?

Potential sources of error in this lab include not using an accurate thermometer, not stirring the solution enough, or not allowing enough time for the solution to reach equilibrium before taking measurements. Also, any impurities in the substances used can affect the results.

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