Abstract: Experimental Molar Mass Of Biphenyl In This Lab ✓ Solved

Abstract In this lab the experimental molar mass of biphenyl

In this lab the experimental molar mass of biphenyl was determined by calculating the molality of cyclohexane solvent. The freezing point depression method is used to find the freezing temperature of the pure solvent. The final molar mass of biphenyl is 148.6 and the percent error was calculated to be 3.6%.

The purpose of this lab was to use the freezing point depression method to determine the molar mass of biphenyl. Dissolving a solute in a solvent can cause the freezing temperature to decrease according to the number of moles in the solute. Therefore, this property depends on the ratio of solute to solvent in a mixture. It is called the freezing-point depression, which is a colligative property.

The freezing temperature of pure cyclohexane was determined by placing 3mL of the substance in a test-tube and then placing it in a 250 mL beaker filled with ice and water. A temperature probe was used to monitor the temperature change, which was then plotted. To calculate the molar mass of biphenyl, approximately 0.1g were measured and added to the cyclohexane. Likewise, the solution was then placed in the ice and water and data was collected for about 10 minutes. This process provided the freezing temperature of the solution, indicated in the graph due to the gradual linear decrease in temperature.

Using the freezing temperature of pure cyclohexane and that of the solution, the change of temperature was calculated. The molality of cyclohexane was calculated, and the weight of the solvent was determined by subtracting the mass of the solution, the mass of the test-tube, and the mass of the biphenyl. By manipulating these equations, the number of moles of biphenyl was determined. Finally, to find the molar mass of biphenyl, the relationship provided the experimental molar mass of biphenyl, calculated as 148.6, compared to the actual value of 154.2.

The molar mass of biphenyl was found to be 148.6 with an average freezing point of pure cyclohexane measured at 7.5°C. The graph illustrates the freezing point as the temperature stabilizes around this value. Table 1 shows the mass measurements used to conduct the experiment. The entire mass of the solution was important to measure in order to find the mass of cyclohexane. The mass of cyclohexane was determined to be 2.25g. The number of moles of biphenyl calculated was divided by the actual mass used. The accepted molar mass of biphenyl is 154.2, resulting in a 3.6% error, which is reasonable given potential errors in the measurement process.

When transferring the biphenyl to the test-tube, some particles remained on the weighing boat, slightly altering the value of the molar mass. Moreover, stirring the solution with a copper stirrer can affect the freezing point depression, as the temperature fluctuates. Adding more biphenyl decreases the freezing point depression, demonstrating that as the solute increases, the freezing temperature decreases. This illustrates the colligative property, dependent on the number of molecules rather than the type of molecules present in the solution. Losing some solid biphenyl during transfer affects the measured molecular weight because it is calculated by dividing mass by the number of moles, meaning the measured molecular weight will be lower than the actual due to loss during transfer.

Paper For Above Instructions

The determination of the molar mass of biphenyl through the freezing point depression method is a prevalent technique in physical chemistry. This colligative property has significant applications in both academic research and industrial processes, thereby enhancing the understanding of solute-solvent interactions. Biphenyl, an organic compound composed of two phenyl groups, has various applications including its use in organic synthesis and as a heat transfer medium.

The objective of this experiment was to accurately determine the molar mass of biphenyl by utilizing the freezing point depression technique, observing how the addition of a solute affects the freezing point of a solvent—in this case, cyclohexane. The data collected from this experiment confirms the theoretical relationship stated by Raoult's Law and allows for the calculation of molality and ultimately the molar mass of biphenyl.

The method employed begins with the measurement of the freezing point of pure cyclohexane, through which the change in freezing point can be determined once biphenyl is added to the solvent. According to colligative properties, the depression of the freezing point is directly proportional to the molality of the solute present in the solution. This proportionality can be expressed through the formula:

ΔTf = Kf * m

Where ΔTf is the change in freezing point, Kf is the freezing point depression constant for cyclohexane, and m is the molality of the solution. Identification of Kf is critical for accurate calculations; for cyclohexane, this constant is approximately 20.0 °C kg/mol. The experimental steps involved accurately measuring the mass of biphenyl added to a known mass of cyclohexane, monitored precisely through the collection of freezing point data.

Through the experiment, the measured freezing point of cyclohexane was around 7.5 °C with the presence of biphenyl, which indicated a significant decrease from its normal freezing point of approximately 6.6 °C. This reduction allows for the calculation of molality:

m = (mass of solute in kg) / (mass of solvent in kg)

The molar mass can then be derived using the following relationship:

Molar Mass = (mass of solute in grams) / (number of moles of solute)

This experiment resulted in a calculated molar mass of 148.6 g/mol for biphenyl, differing slightly from the accepted value of 154.2 g/mol. The percent error of 3.6% can be considered acceptable within the realm of experimental chemistry, acknowledging the potential inaccuracies inherent in lab settings such as temperature fluctuations and measurement inaccuracies.

Further improvement for this experiment may involve ensuring consistent environmental conditions, use of high-precision measuring devices, and minimizing the loss of biphenyl during transfer processes. Addressing these factors can potentially lower the percent error in future experiments.

In conclusion, this lab successfully applied the freezing point depression method to determine the molar mass of biphenyl, reinforcing theoretical concepts of colligative properties while promoting practical skills in empirical laboratory work. Understanding these relationships is vital for further explorations in both academia and industry.

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