Observations And Data: Mark Table 1 Masses Of Solvent And So

Observations And Data1 Mark Table 1 Masses Of Solvent And Solute Us

Observe that the data provided includes various measurements related to the masses of biphenyl (solvent) and an unknown substance (solute) used in an experiment to determine the molar mass of the unknown via freezing point depression. The dataset includes the masses of the sample vials and biphenyl, the amounts of biphenyl and unknown added, as well as the freezing points of pure biphenyl and the biphenyl solution containing the unknown over multiple runs. Specifically, the freezing points are used to calculate the freezing point depression caused by the unknown, which serves as the basis for determining its molar mass.

The key data points are as follows: the pure biphenyl freezing point averages around 68.2°C; the solution freezing points average around 60.7°C; and the freezing point depression is approximately 7.5°C, calculated from the difference. Using the masses provided, the molality of the solution can be calculated, which then allows for the determination of the molar mass of the unknown. These calculations are essential to identifying the unknown substance by comparing it with known molecular weights.

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Understanding the physical properties of substances, such as melting points and freezing points, provides vital information about their molecular characteristics. In this experiment, the primary goal was to determine the molar mass of an unknown compound by analyzing the freezing point depression of biphenyl, which acts as the solvent. By carefully measuring the freezing points of pure biphenyl and the biphenyl solution containing the unknown, and applying colligative property principles, it is possible to infer the molecular weight of the unknown substance.

The initial data involved precise measurements of the masses of biphenyl and the unknown compound. For biphenyl, the combined mass of the vial and biphenyl was recorded as 15.534 g, with the empty vial weighing 14.00 g, leading to a biphenyl mass of 2.110 g. Similarly, for the unknown, the combined mass with the vial was 13.440 g, and the empty vial was 13.123 g, indicating an unknown mass of 0.240 g after subtracting the empty vial's weight. These measurements form the basis for calculating the molality of the solution, which depends on the number of moles of solute and the mass of the solvent in kilograms.

Freezing point data were recorded over three runs for both pure biphenyl and the biphenyl-unknown solution. The average freezing point of pure biphenyl was approximately 68.2°C, which aligns with literature values, indicating the measurements are reliable. The solution's freezing points were lower, averaging about 60.7°C, revealing a freezing point depression of 7.5°C. This depression reflects the presence of the unknown compound dissolved in biphenyl, which disrupts the crystal lattice and lowers the freezing point, consistent with colligative properties.

Using the formula for freezing point depression:

ΔTf = Kf × molality

where ΔTf is the freezing point depression, and Kf is the cryoscopic constant of biphenyl, known to be approximately 7.6°C·kg/mol, the molality of the solution can be calculated. For ΔTf = 7.5°C, the molality (mol of solute per kg of solvent) is:

Molality = ΔTf / Kf = 7.5 / 7.6 ≈ 0.987 mol/kg

Given that the mass of biphenyl (solvent) used was 2.110 g or 0.00211 kg, the number of moles of the unknown is:

moles of unknown = molality × mass of solvent in kg = 0.987 mol/kg × 0.00211 kg ≈ 0.00208 mol

The molar mass of the unknown is then calculated using its mass:

Molar mass = mass of unknown / moles of unknown = 0.240 g / 0.00208 mol ≈ 115.4 g/mol

This estimated molar mass of approximately 115.4 g/mol guides the identification. Based on common molecular weights of molecules introduced in such experiments, this value corresponds closely to several organic molecules, including certain alcohols or small aromatic compounds. The limited experimental error and the precise measurements lend confidence to this estimation, although confirming the identity would require additional spectroscopic or chemical tests.

In conclusion, the colligative property experiment effectively allows for the determination of the molar mass of an unknown substance dissolved in biphenyl. The derived molar mass strongly suggests the unknown is a compound with a molecular weight around 115 g/mol, consistent with specific candidates discussed in the relevant chemical literature. Such experiments highlight the importance of careful measurement and theoretical application in analytical chemistry for qualitative and quantitative analysis of compounds.

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