Introduction
The objective of this experiment is to study the effect of a solute on the freezing point of a solvent. When a solute is added to a pure solvent, the freezing point of the solvent is lowered as compared to its pure form. This decrease in freezing point of the solvent is known as “Freezing Point Depression”. A similar phenomenon occurs in the boiling of such solvents, but instead of decreasing, the boiling point is increased due to the addition of the solute. This phenomenon is known as “Boiling Point Elevation”. Such phenomena, including others, are known as colligative properties. The decrease in the freezing point depends on the nature of the solute that is added to the pure solvent.
Experimental
This experiment will be conducted in two parts. The first part is to determine the freezing point of an alcohol and water mixture. This is achieved by analyzing the cooling curve obtained from the experiment with the help of the Vernier LabPro Box and Logger Pro software. Before the freezing point of the alcohol/water mixture is determined, the test should be run using pure water. This allows to determine a baseline freezing temperature. This experiment involves studying the cooling characteristics of the assigned alcohol according to the procedure highlighted in the lab manual. The second part of the experiment is to determine an unknown from the change in the freezing point. This is achieved by determining the change in freezing point which is expected for the alcohol being used in the experiment at a number of different concentrations. Thus, the molecular weight of the unknown alcohol needs to be determined.
Results
Observations and Data
The experiment starts at 24°C. 10.02 gram of 1.Propanol is weighed to be used in the experiment.
Given Constant 1.86°C
∆Tp 1.861.66=-3.09°C
0.0°C--3.09=3.09°C
Part 2
Part 2 involves the performance of the experiment with the unknown alcohol.
According to the data obtained from part 2, it may be said that the unknown alcohol was found to be ethanol.
Tp=-6.362°C
3.5∆T=1.86
m=1.88molkg=.188 10g
=1.88 mol weight
=1.88 g/mol
Discussion
The freezing of the alcohol obtained from the data from the experiment was found to be low as compared to the freezing point of the pure alcohol. The lowering of the freezing point is what was being investigated in the experiment. It may be observed that the addition of an impurity alters the freezing point, or drops it to be exact. This is what was observed in this experiment as well. The trend in the data of the different alcohols might be clearly observed. The temperature of the different alcohols lies within a close range and these temperatures are pretty close to one another. Another trend that is observed from the obtained data of the different alcohols is that the change in temperature, i.e. ∆T, is almost constant and remains within a certain range. The values in the range do not vary much and are very close to one another when the temperatures of the different alcohols are compared. This may be pointing to the fact that all the alcohols have very identical characteristics.
The freezing point obtained from the data obtained from the experiment may be a little deviant from the freezing point of the pure alcohol. However, the difference is small. Such a difference is admissible and may be explained with the help of the errors that may have happened during the course of the experiment. The errors that may be induced in the experiment include an error in the measurement of temperature i.e. an error in the calibration of the instrument measuring and recording the data. Such an error will propagate through the experiment and all the observations and data recorded through the instrument without the experimenter knowing it. Thus, care needs to be exercised in this matter and the calibration of the instrument should be ensured.
Other errors might result from the unintentional addition of impurities apart from the ones that are part of this experiment and need to be added for the completion of this experiment. As this experiment also suggests, that the addition of impurities may alter the freezing point. The addition of any impurity might have altered the freezing point and thus it will propagate an error into the experiment which will then be reflected in the obtained data and in the results.
The second part of the experiment was conducted as instructed in the lab manual. It was found through the observations that the provided unknown alcohol may have been ethanol. This was interpreted as a result of the obtained data and the molecular weight.
Conclusion
The experiment was conducted as instructed in the lab manual and the effect of the addition of impurities to the solvent was studied. Firstly, the freezing point of water was observed through the experiment to all for the settlement of the baseline freezing temperature. The second step was to find the freezing point of the alcohol and water mixture which was completed according to the instructions found in the lab report. The final step was to find out the unknown alcohol by repeating the steps in the first part and finding out the molecular weight of the alcohol. The alcohol was found to be ethanol. This conclusion was based upon the molecular weight of the alcohol found through calculations and experimentally. The fall in the freezing point of the alcohol was observed due to the addition of water to the alcohol. The freezing point depression phenomenon was clearly observed in this experiment.
