Saul Ruiz Chemistry 1CL April 22 2012 Experiment 17 Colligative Properties Freezing Point Depression Colligative properties of solutions are those that are affected by concentration and as the title suggests the freezing point is determined for a pure benzophenone solution along with a benzophenone cyclohexane mixture in this experiment By utilizing the known fact that the freezing point of depression for a dilute solution is directly proportional to the molality m and by measuring Tf for dilute solutions of known molality the freezing point depression constant can be solved for T f i K f m The magnitude of Tf depends on the number of particles in a solution whereas the factor i accounts for the moles of particles formed when electrolytes dissociate to form ions in solution In the first part of the experiment the benzophenone solution is first heated and then allowed to equilibrate to room temperature noting when crystals first form and recording the data for further analysis The process for Part 2 of the experiment is similar to the first part and at the end the temperature is also measured every ten seconds and recorded This data from both parts are graphed in order to determine the freezing point of the solutions as well as the freezing point depression constant Kf in order to compare them to the actual values and determine a numerical percent error The experimental value for the freezing temperature of benzophenone Tf was determined to be 45 9 C which when compared to the actual freezing point of 47 8 C it resulted in a 3 975 error This error is attributable to several sources of error that were present in this experiment Despite the fact that the imprecision of the instruments used is not technically a source of error it had a particularly detrimental effect on the results This in turn restricts the accuracy of the final result The freezing point curve for pure benzophenone depicts a gradual decrease in temperature up to the lowest point which is at around 210 seconds Afterwards it levels off and stays constant The freezing point curve for the benzophenone cyclohexanone solution cyclohexanone is added shows a sudden drop in the first few seconds and after it hits the lowest point at around 100 seconds it gradually begins to rise in temperature The third graph which is the freezing point curve for the benzophenone cyclohexanone solution more benzophenone is added maintains a gradual decrease in temperature throughout the entire recording time The Tf for the first solution containing cyclohexaone turned out to be 9 4 C whereas the Tf C kg for the second solution was 7 5 C Their respective Kf were calculated to be 9 731 mol C kg C kg Therefore the average Kf resulted to be 10 69 The accepted mol mol C kg value of benzophenone is 8 70 whereas the average value that was calculated for Kf mol C kg was 10 69 returning a percent error of 22 87 mol and 11 646 Possible sources of error in this part of the experiment could stem from the inaccuracy of certain instruments such as the thermometer which was not able to properly determine the temperature of the solution Temperature appears to be the least precise measurement in this lab because the readings are rounded to only one decimal place compared to the rest of the calculated values which could also affect the results of the experiment due to rounding error Another source of error could be that some of the solute benzophenone could have been lost either after being weighed or after the solute and solvent were mixed but before the freezing point was determined This would result in less solution than what was necessary to complete the experiment Therefore if the lab were to continue like this then the freezing point of the solution would be different due to the fact that there are not as many dissolved particles within the solution