paraphrase

Abstract:

             The purpose of this lab was to use the freezing point depression method to determine the freezing temperature of pure cyclohexane and the freezing temperature of a solution of the biphenyl and cyclohexane. In addition, using the equation of freezing point to find the molality of the solution. The observation of this experiment was that, the freezing point would be decreased when the biphenyl was added more than pure cyclohexane itself. This was happened because while adding the solute to the solvent, the vapor pressure will decreased then the freezing point would decreased too. The result of this lab was that, the molar mass of biphenyl was 142.4gram per mole with percent of error 7.5 %.

Introduction:

             The main idea of this lab was to find the molar mass of biphenyl by using the freezing point depression method. Therefore, Freezing point depression is defined as the process of adding a solute to a solvent to decrease the freezing point of the solvent. For example, adding the salt to the pure water. Moreover, the effect of added more solute to the solvent is decreasing the amount of the vapor pressure and increase the boiling point of the substance. Therefore, the freezing point depression depends on the ratio of the solvent and solute particles. The equation that can explain the relationship between the freezing point depression and the molality is delta T = Kf * m. Where Delta T is the freezing point depression, Kf is the constant of the freezing point depression and m is the molality of the solution. Therefore, this equation was used to find the molar mass of biphenyl in gram per mole.

Discussion:

       In this experiment, we had done four trails started with two tubes that contain a pure Cyclohexane. In this two, the freezing point has been found by using the Logger Pro program. After that, we added the Biphenyl two tubes to created a solution. The addition of the Biphenyl solute to the Cyclohexane causes many effects. The freezing point depression became lower than the freezing point of the cyclohexane itself. As result, the molar mass of the Biphenyl was 142.5 gram per mole with percent of error 7.5% and this value was less than the accepted value. I think the source of error that made the value less than the accepted value would be the assumption of the amount of the solvent and the solute for this experiment.

Questions:

In the past, many students have listed that they accidentally lost some of the solid biphenyl during transfer to the test tube. What will be the expected effect on the

measured molecular weight?

I think the expected effect on the measurement of molecular weight would be that, the value of the molecular weight or molar mass will not be exactly correct and it would be less than the accepted value of the molecular weight of the Biphenyl.