Solve Molality to Mass Homework Problem

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SUMMARY

The discussion centers on calculating the mass of an unknown solute needed to achieve a molal concentration of 0.416 mol/kg in cyclohexane. The freezing point depression (ΔTf) was determined to be 5.2°C, with cyclohexane's cryoscopic constant (Kf) at 12.5°C/molality. To find the mass of the unknown solute, the formula for molality (m = moles of solute/kg of solvent) must be utilized, along with the molar mass of the solute, which remains undetermined until the mass is calculated.

PREREQUISITES
  • Understanding of freezing point depression and its relation to molality
  • Familiarity with the formula for calculating molality (m = moles of solute/kg of solvent)
  • Knowledge of cryoscopic constants (Kf) and their application in colligative properties
  • Basic skills in stoichiometry and molar mass calculations
NEXT STEPS
  • Review the concept of freezing point depression and its formula
  • Learn how to calculate molar mass from molality and mass of solute
  • Study examples of colligative properties in solutions
  • Practice problems involving Kf values and their applications in determining solute concentrations
USEFUL FOR

Chemistry students, particularly those studying physical chemistry or solution chemistry, and educators looking for practical examples of colligative properties in laboratory settings.

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Homework Statement


Hi. This is a question based on a lab I did.

We mixed an unknown solute in a solution of pure cyclohexane. Based on numbers we got from our lab, we were asked to find the molal concentration of the unknown. The freezing point of the unkown was found to be 1.5 C and the freezing point of the cyclohexane was found to be 6.7 C. Therefore Delta Tf is 5.2 C. the Kf of the cyclohexane was found to be 12.5 C/molality.

so i found the molality of the unkown to be .416 mol/kg

we are asked now to find the mass of the unkown that would dissolve in 1kg of cyclohexane to give the same molal concentration that we had in our solution.

i'm not seeing how the heck i can find mass from this the information I have.

We will lastly have to find the molar mass of the unkown. I can't find this until i have figured out the mass of the unkown

any help would be appreciated! thank you


Homework Equations





The Attempt at a Solution

 
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Please describe precisely the experiment as it was done and all information you were given. I agree that at present there is not enough data, but could be you are ignoring some crucial information not seeing how it is related to the question.

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methods
 

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