Chemistry Lab

Chemistry Lab Lab Report Introduction: The purpose of this lab was determining the molecular weight of an unknown solid organic compound by freezing point depression. In order to do so, one has to first, freeze cyclohxane, by putting it in ice cold water, and see what the constant temperature comes out as. Then, one has to freeze .4 grams of there unknown, and cyclohexane by doing the same process and also see what the constant temperature will come out as. After figuring out your constant temperature, on should then plug their numbers into the equations. Procedure: These equations were given in the lab procedures for experiment number ten Experiments for General Chemistry at Yavapai College Pure Impure temp time temp time 23.8 15 24.2 15 21.8 30 22.3 30 16.7 45 16.4 45 12.4 60 12.1 60 10.2 75 9.9 75 9 90 8.7 90 7.9 105 8 105 7.5 120 7.6 120 7 135 7.5 135 6.7 150 7.3 150 6.4 165 7.1 165 6.4 180 6.9 180 6.4 195 6.7 195 6.4 210 6.5 210 6.4 225 6.5 225 6.4 240 6.5 240 temp time temp time 25.5 15 19.7 15 22.7 30 16.5 30 15.7 45 11.5 45 10.8 60 8.4 60 7.9 75 6.5 75 6.1 90 5.4 90 5 105 4.2 105 4.2 120 3.5 120 3.1 135 3.1 135 2.8 150 2.8 150 2.7 165 2.6 165 2.6 180 2.5 180 2.5 195 2.5 195 2.2 210 2.4 210 2.2 225 2.4 225 2.2 240 2.4 240 Pure Substance Impure Substance Results and Calculations: Molality = moles of solute/Kilograms solvent Density = 0.77g/ml D = Mass/volume Volume = 25ml (.77g/ml) = (m/25ml) 19.25/g (1kg/1000g) 4.3 = 20* ml *m = 19.25g = .01925k M = .215 (.215M) = (.4012/ mw) / (.01925 kg) = (.00414M) = (.4012/mw) = (.4012) / (.00414M) = 96.908mw Conclusion: The results for this experiment turned out as the molecular weight being 96.9.

The weight of unknown originally was 128; therefore the molecular weight that was calculated was only off by 31.1. The percent error of the whole experiment was 34.3%. The only thing that could have semi contaminated this experiment was the rust from the stirrer. Other than that, there is nothing else the experimenter can think of. Science.

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