CM1131_practical_1 - CM1131 Name: _ Lab Group: B1 Date:...

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CM1131 Name: ________ Date: 21-Mar-07 Lab Group: B1 LAB REPORT E XPERIMENT 1 DETERMINATION OF MOLECULAR MASS BY BOILING PPOINT ELEVATION A IM To determine the molar mass of an unknown compound by measuring the elevation of boiling point of ethanol. I NTRODUCTION Determining the molar mass of an unknown compound by boiling point elevation makes use of the colligative properties of dilute solutions. These colligative properties are: boiling point elevation (ebullioscopy), freezing point depression (cryoscopy), vapor pressure lowering, and osmotic pressure. Colligative properties are properties which depend only on the concentration of solute in a solvent, and not on the type of solute. The expression relating boiling point elevation to molality is: ΔT = iK b m Where m = molality of the solution K b = ebullioscopic constant of the solvent i = van’t Hoff factor Assuming the van’t Hoff factor to be 1 in the case of an organic solvent ethanol, the expression is simplified to ΔT = K b m. 1
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R ESULTS Sample: 8 1. Volume of ethanol used: 25cm 3 2. Temperature of boiling point of pure ethanol (T 2 ): 77.8°C 3. Mass of empty test tube: 14.3688g 4. Mass of unknown + test tube, ( w 1 ): 17.7053g 5. Mass of residual unknown + test tube, ( w 2 ): 14.3780g 6. Mass of unknown added, ( w 1 - w 2 = w ): 3.3273g 7. Temperature of boiling ethanol with added unknown, (T
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CM1131_practical_1 - CM1131 Name: _ Lab Group: B1 Date:...

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