Colligative properties: Freezing-point depression and molar mass. 1- Volume of c

Question

Colligative properties: Freezing-point depression and molar mass.

1- Volume of cyclohexane: 10.0 mL, density=.7726 g/mol

2- Mass of cyclohexane

3- Show calculation

4- Mass of unknown 0.347g

A- Warming Curve Data-Pure Cyclohexane

Trial 1 Temp C Time

7.1

  

B. Warming Curve Data-Solution containing unknown 2

Trial 1

Temp C Time

12- Delta t ________________ C

13- Molality of unknown (show calculations)

14- Molar mass of unknown (show calculations) ___________

Time Temp in celsius 0 7.0 60

7.1

90 7.4 120 7.5 150 7.7 180 8.0 210 8.1 240 8.1 270 8.2 300 8.3 330 8.6 360 8.9 390 9.3 410 9.5 440 9.8 470 10.1 500 10.3 530 10.6 560 10.8 590 11.0 620 11.3 650 11.5 680 11.8 710 12.1

Explanation / Answer

2. Mass of cyclohexane = volume x density = 10 x 0.7726 = 7.726 g = 0.007726 kg

12. dT from B. = 8.0 oC

dTf = i.Kf.m

13. molality of unknown = 8/20.2 x 1 = 0.396 m

14. molar mass of unknown = 0.347 g/0.396 m x 0.007726 kg = 113.42 g/mol

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