Determining molar mass by freezing point depression lab

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SUMMARY

The discussion centers on calculating the molar mass of an unknown substance using freezing point depression in a biphenyl solution. The student calculated the cryoscopic constant (Kf) of biphenyl as 81.2 °C kg/mol. Given a solution with 1.64 g of the unknown in 18.22 g of biphenyl that froze at 39.9 °C, the freezing point depression and molality must be determined. The relationship between molality and molar mass is critical for solving the problem accurately.

PREREQUISITES
  • Understanding of freezing point depression and its formula.
  • Familiarity with the concept of molality and its calculation.
  • Knowledge of the cryoscopic constant (Kf) and its application.
  • Basic skills in algebra for solving equations related to molar mass.
NEXT STEPS
  • Review the freezing point depression formula: ΔTf = Kf * m.
  • Learn how to calculate molality: m = moles of solute / kg of solvent.
  • Study the properties of biphenyl and its use in cryoscopic measurements.
  • Explore examples of molar mass calculations using freezing point depression.
USEFUL FOR

Chemistry students, educators, and laboratory technicians involved in physical chemistry experiments and those seeking to understand colligative properties and their applications in determining molar mass.

kevin0788
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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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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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