4 CHM151LL D ETERMINATION OF M OLAR M ASS BY F REEZING P OINT D EPRESSION Name

4 chm151ll d etermination of m olar m ass by f

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4 | CHM151LL: D ETERMINATION OF M OLAR M ASS BY F REEZING -P OINT D EPRESSION Name Partner Score Data Table 1. Pure lauric acid time (s) temperature (°C) time (s) temperature (°C) time (s) temperature (°C) 0 220 440 20 240 460 40 260 480 60 280 500 80 300 520 100 320 540 120 340 560 140 360 580 160 380 600 180 400 620 200 420 640 Mixture number: lauric acid in mixture g benzoic acid g Data Table 2. Benzoic/lauric acid mixture time (s) temperature (°C) time (s) temperature (°C) time (s) temperature (°C) 0 220 440 20 240 460 40 260 480 60 280 500 80 300 520 100 320 540 120 340 560 140 360 580 160 380 600 180 400 620 200 420 640
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CHM151LL: D ETERMINATION OF M OLAR M ASS BY F REEZING -P OINT D EPRESSION | 5
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6 | CHM151LL: D ETERMINATION OF M OLAR M ASS BY F REEZING -P OINT D EPRESSION Calculations Freezing-point depression of the benzoic/lauric acid solution: Molal concentration (also called molality ) of benzoic/lauric acid solution: Amount of benzoic acid solute: Molar mass of benzoic acid (experimental value):
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CHM151LL: D ETERMINATION OF M OLAR M ASS BY F REEZING -P OINT D EPRESSION | 7 Molar mass of benzoic acid (expected value): Molar mass percent difference:
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8 | CHM151LL: D ETERMINATION OF M OLAR M ASS BY F REEZING -P OINT D EPRESSION Name Date Score Post-laboratory Assignment For full credit, show the detailed steps of each calculation below. Use more paper if needed. 1.The freezing point of a solvent is 87.0 °C. When a 0.163-g sample of C7H6O2was added to 4.18 g of the solvent, the solution had a freezing point of 82.5 °C. Find Kffor the solvent. 2.Given a compound’s molar mass (99 g/mol) and elemental percent composition (48.5% C, 5.05% H, 14.1% N, and 32.3% O by mass), determine the compound’s molecular formula. 3.Draw a possible Lewis structure of the compound described in question 2. In any correct structure, all atoms obey the octet rule and have zero formal charge.
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