Separation of Cyclohexane and Toluene
Introduction:
The purpose of this experiment was to separate an organic liquid mixture of cyclohexane (C6H2) and toluene (C6H5CH3) by simple or fractional distillation and to analyze each distilled fraction by gas chromatography. Cyclohexane Toluene Molecular Weight: 84.16 g/mol Molecular Weight: 92.14 g/mol
Distillation is a method used for the separation of liquid mixtures into their purer forms by their differences in boiling point. It works by heating the liquid mixture enough for each compound’s boiling point to be reached. When heated enough, the more volatile (lower boiling point) compound will begin to vaporize. The vapor then travels through the distillation apparatus and begins to condense; separating it from the compound with the higher boiling point. When deciding which type of distillation to use, the boiling points of each substance in the liquid mixture must be compared. If there is a significant difference in the boiling points of each compound, greater than 70°C, then it is acceptable to use simple distillation. Simple distillation can separate compounds in a single vaporization step. On the other hand, if the difference in each boiling point is not as great then fractional distillation must be used. We performed both types of distillation individually to separate our cyclohexane and toluene mixtures in order to determine which type was more effective. The literature values for the boiling points of cyclohexane and toluene are; 85.0°C for cyclohexane and 110.0°C for toluene. Based on this information I hypothesized that fractional distillation would be the more effective method in separating our mixture considering the difference in boiling point was <70°C (d=29.86°C).
A simple distillation apparatus is similar to fractional with the difference being that the fractional set-up includes a fractional column separating the distilling flask from the distilling head. This fractional column provides a larger surface area inside the column, which helps cool and condense the rising vapor. This better ensures that the vapor that reaches the top of the column is composed entirely of the more volatile compound.
To determine the relative separation efficiency of simple and fractional distillation we analyzed our samples using gas chromatography. We used this method to separate the volatile organic compounds to detect and determine the concentration of cyclohexane and toluene in each of our distillation fractions.
Experiment:
After setting up our distillation apparatuses (simple and fractional), we attained 24 mL of a 50% cyclohexane and 50% toluene mixture and added this to our boiling flask in each apparatus along with our boiling chips. We then started to slowly heat the mixture to boiling, and once brought to a boil we adjusted our heater to decrease the rate of distillation to 1 drop per second for simple and 10-20 drops per minute for fractional. Our first few drops were collected in a waste beaker and discarded.
We collected three fractions for both simple and fractional distillation. For simple distillation we separated our fractions by volume; approximately 7 mL per fraction. Before we started to collect our fractions we measured 7 mL of water in a graduated cylinder and poured that into a test tube; allowing us to etch a level marker on each test tube to see where to stop collecting each fraction. The first fraction collecting the first 7 mL (F1 volume: 7.2 mL), the second collecting the second 7 mL (F2 volume: 6.6 mL), and the third collecting the third 7 mL (F3 volume: 7.2 mL). For our fractional distillation we separated our fractions by changes in temperature. After the first few waste drops were collected and discarded the temperature appeared to plateau and this is when we started to collect our first fraction until the temperature started to rise again (F1 volume: 9.2 mL). The second fraction was
