Lab 7 ochem 2 distillation PDF

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Name: Xiomara Aragon

Date: 3/13/2020

Lab Report: 7

Lab Report: Experiment 07: Separation and Purification of Organic Liquids

Introduction: Distillation is a process that is used to purify and identify organic compounds. Moreover, the process of distillation can be applied to everyday life. For example, vodka is distilled, which increases the concentration of ethanol, in order to make it stronger. Distillation occurs when a liquid is heated to a boiling point and the vapors condense above the boiling point. The whole process consists of three general steps: separation, evaporation and condensation. The capacity to separate a mixture of different liquids depends on each of the liquids ability to vaporize. The liquid that contains the highest vapor pressure is always higher in concentration and will therefore be collected first. There are two different vaporization techniques that can be implemented in an organic chemistry laboratory: simple distillation and fractional distillation. Simple distillation takes the boiling liquid in a distilling flask and directs the liquids vapors through a condenser. These vapors are then cooled and converted back into a liquid that flows into a receiving flask. Fractional distillation is very similar to simple distillation but differs in that a fractioning column is placed in between the distilling flask and the condenser. It is this fractioning column that allows for repeated vaporizations and condensations to take place, which in turn allows the mixture to separate into its respective liquids much better. Fractioning distillation works better than simple distillation when the difference in boiling points, between the liquids, is small. For instance, a difference between 10°C and 15°C would be optimal. When conducting a distillation, it is also important to understand several other concepts. These are boiling points of liquids, Raoult’s Law, Dalton’s Law and azeotropes. It is the molecule’s intermolecular forces that determine a liquids boiling point. Moreover, molecules with stronger intermolecular forces tend to have higher boiling points. The strength of intermolecular forces is affected by molecular weight, the branching in the molecule and the presence of hydrogen bonds. Additionally, the boiling point occurs when the vapor pressure exceeds the atmospheric pressure. Raoult’s Law states that the vapor pressure of a solvent above a solution is equal to the vapor pressure of the pure solvent at the same temperature, when scaled by the mole fraction. Whereas, Dalton’s Law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases. Finally, an azeotrope is a mixture of liquids that has a specific boiling point and the composition does not change as it is distilled. Moreover, the boiling point can be higher or lower than the pure components. The aim of this experiment was to separate a one to one mixture of cyclohexane and toluene using simple and fractional distillation, and to compare the two distillation techniques using a temperature versus volume graph.

Procedure: Separation of a two-component mixture by a simple distillation: 10 mL of acetone and 10 mL of toluene were combined, then the mixture was distilled using the simple distillation setup. Insert a boiling chip before heating the mixture. The temperature was recorded for every 2 mL of distillate collected in the graduated cylinder. The round bottom flask was not let to run dry.

Separation of a two-component mixture by a fractional distillation: 10 mL of acetone and 10 mL of toluene were combined, and the mixture was distilled using the fractional distillation setup. The temperature was recorded for every 2 mL of distillate collected in the graduated cylinder. The round bottom flask was not let to run dry.

Data and Observations: Distillation of two component mixture: mL distilled Temp °C distillatio n Temp °C factional distillatio n

2

4

6

8

10

12

14

16

44°C

49°C

48°C

43°C

36°C

69°C

77°C

80°C

38°C

43°C

40°C

35°C

50°C

75°C

Some of the temperatures shown in the table might have been different because the mixture was separating due to their different boiling points.

Conclusions: Seeing the mixture being condensed, it was noticed that the condenser might have been contaminated as the liquid changed to a light brown color....