A student determines the molar mass of acetone, CH3COCH3, by the method used in this experiment. The student found that freezing temperature of water was 1.0 oC. When the student added 11.1 g of acetone to the ice/water equilibrium mixture at this temperature, the temperature fell to -3.0 oC. The student promptly decanted the solution into a beaker and determined the mass of the solution to be 90.4 g. a) What is the freezing point depression? ___________________ b) What is the molality of the solution?
Bristol Community College
Fall River, Massachusetts
Experiment 6: Molar Mass of a Molecular Solid from Freezing Point-Depression
Measurement
Name: __________________________________ Date: _______________
Approved: ___________
DATA SHEET
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Mass of lauric acid (in Part II) |
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Mass of benzoic acid (in Part II) |
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Freezing temperature of pure lauric acid (from Part I) data from Video 2 of Part I |
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Freezing temperature of solution (from Part II) data from Video referenced in Part II |
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Freezing point depression, Tf ( = Tf, lauric acid – Tf, solution) |
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Molality (m) of solution ( Eq. 1) |
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Moles of benzoic acid ( Eq. 2) |
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Experimental molar mass of benzoic acid (Eq. 3) |
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Calculate the molar mass of benzoic acid, C6H5COOH. |
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Percent error |
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Summary Questions
- A student determines the molar mass of acetone, CH3COCH3, by the method used in this experiment. The student found that freezing temperature of water was 1.0 oC. When the student added 11.1 g of acetone to the ice/water equilibrium mixture at this temperature, the temperature fell to -3.0 oC. The student promptly decanted the solution into a beaker and determined the mass of the solution to be 90.4 g.
- a) What is the freezing point depression? ___________________
- b) What is the molality of the solution?
- c) How much acetone was in the decanted solution?
- d) How much water was in the decanted solution?
- e) What did the student find to be the molar mass of acetone, assuming the student made the calculation properly?
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