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Objective: Learn and understand the process of distillation which allows us to separate two substances in the liquid state of matter into their pure forms. Distillation and recrystallization allow for their reactants to be purified and their products to be collected to test the effectiveness of each process. By performing distillation, we will gain a better understanding of the ways pure substances can be made in the lab.
Compounds of Study:
Cyclohexane
Cyclohexane
Formula: (C6H12)
Boiling Point: (78 oC)
Molar Mass: (84.16 g/mol)
Image from ChemSpider
Toulene
Toulene
Formula: (C6H5CH3)
Boiling Point: (111 oC)
Molar Mass: (92.14 g/mol)
Image from ChemSpider
Pre Lab:
What is the property of refraction? In other words, when you are testing the refractive index, what are you testing for?
Refraction occurs as light passes from one medium to another and there is a difference between the "index of refraction." When you create an index of refraction for a given compound, you test the absorbance of the compound at various concentrations using a spectrophotometer. This test then creates a graph that can be used to assess the purity of the compound.
2. What kinds of compounds are best separated by distillation?
Water and alcohols.
3. Describe fractional distillation in your own words
Separating compounds based on differences in their vapor pressure through repeated distillation to separate their components.
5. Why is it important not to overheat your flask during distillation?
If the flask is heated too quickly, the contents will never be able to reach equilibrium which is required for the condensation to be able to occur and move into the second flask for collection.
6. Why is it important to use grease in the glass joints? What happens if you use too much? If you use too little?
Using grease will allow the glass to create a good between the components, will allow the glass to be easily moveable, and can prevent accidental breaking of glassware during experimentation. However, using too much grease may contaminate the experiment. If too little grease is used the grease will not prevent sticking as distillation occurs.
7. Why is it important to have cold water flowing through the condenser?
Having cold water in the condenser will allow the vapor to cool and for condensation to occur as the vapors evaporate from the solvent, allowing for a higher yield of the solvent we are trying to isolate from the compound.
8. Describe an azeotropic mixture and the distillation of an azeotropic mixture.
A mixture that has the same concentration in the liquid and vapor phase.
9. When is steam distillation used for purification?
When the boiling point of the solvent is above the boiling point of water.
10. When is vacuum distillation used for purification?
When the expected boiling point is higher than both water and steam.
11. What is the purpose of activity #1 for this lab? Why are you creating a calibration curve?
The purpose of activity #1 is to create a calibration curve! We are creating a calibration curve that
can be used to determine the concentration of an unknown substance by comparing it to other known substances.
12. What material should distill first, cyclohexane or toluene? How did you come to this conclusion?
Cyclohexane should distill first due to its lower boiling point.
13. What is the difference between the distillations in activity #2 and activity #3 in this lab? Which activity should more effectively separate cyclohexane and toluene?
For this lab, we should use simple distillation because the boiling point difference between the cyclohexane and toluene is larger than 25 C.
Activity #1: Refractive Index Calibration Curve
Experimental:
My partner and I selected 50% cyclohexane with 50% toluene and 25% cyclohexane with 75% toluene solutions to test the refractory index of.
The solutions were prepared in 10 mL quantities.
Refractory indexes were taken using the RI machines available in the lab.
Results:
The lab collected calculated RI value for 50% cyclohexane with 50% toluene is 1.4617.
The lab average value for 50% cyclohexane with 50% toluene is 1.4634
The lab collected calculated RI value for 25% cyclohexane with 75% toluene is 1.4763.
The lab average value for 25% cyclohexane with 75% toluene is 1.4753
RI indexes as collected by the members of the lab sections.
Average RI index as collected by the members of the lab sections.
Activity #2: Distilation
Experimental:
Set up the distillation apparatus experiment for both simple and fractional distillation procedures.
Created 60 ml of a 1:1 cyclohexane to toluene solution using 30 ml of each material that was used in both types of distillation. The hearing apparatus was kept at 65 volts for the majority of the lab.
The solution began to boil after approximately 45 minutes.
For the simple distillation procedure, the solution was collected every 3 ml.
The RI value and temperature were recorded every ~ 3 ml.
The distillation process was stopped when the solution reached 105 degrees Celsius and the RI value read 1.4938.
The product of fractional distillation began forming after about 1 hour and 15 minutes on heat with the hot plate being set to six.
The distilled product was collected every ~ 3 ml.
Temperature was recorded every ~ 3 ml along with the RI value, this will be used to form a graph.
The distillation process ended when the temperature of the solution reached 104 degrees Celcius and the RI value read 1.4967.
At the completion of all lab activities, the distillation equipment was dismantled and all collected distillate plus the remaining solution were disposed of into proper disposal containers available in the lab.
Activity #3: Distilation Calculations and Plots
Simple Distilation Results:
Simple Distilation Data:
distillation Lab for morgan.pdf
*Volume is measured in ml and temperature is measured is Celcius.
Fractional Distillation Results:
Fractional Distilation Lab Data:
distillation Lab for morgan (1).pdf
*Volume is measured in ml and temperature is measured is Celcius.
Discussion and Conclusions:
Simple:
After the simple distillation process had been completed, the data was then used to determine the concentration of cyclohexane that had been distilled as each 3 ml interval was collected. As indicated by the graphs above, as temperature increases, the total volume in ml collected also increases. At a temperature was 105 °C the concentration of cyclohexane was determined to be zero as the RI value was 1.4938 which is a 0.00075 difference from the average RI value calculated for a solution of 100% toluene and 0% cyclohexane in activity #1. It is important to mention that there is a notable outlier date present toward the beginning of the experiment. Even if the procedure was executed with accuracy, this large dip in the graph indicates that the recording part of IR was either not performed with a high level of skill, there were probably many droplets on the IR machine when the sample was tested, or it was contaminated from other group's experiment.
Fractional:
After the fractional distillation process had been completed, the data was then used to determine the concentration of cyclohexane that had been distilled as each 3 ml interval was collected. As indicated by the graphs above, as temperature increases, the total volume in ml collected also increases. At a temperature was 104 °C the concentration of cyclohexane was determined to be zero as the RI value was 1.4967 which is a 0.00215 difference from the average RI value calculated for a solution of 100% toluene and 0% cyclohexane in activity #1.
Both the data sets suggest that as the temperature of the distillation increases the percentage of cyclohexane decreases. As the percentage of cyclohexane decreases the RI value increases.
Reflections:
This lab asked that my lab partner and I combine several skills that we have been developing throughout the course of the semester, such as time management skills, reading comprehension, critical thinking, and problem-solving skills. Due to unfamiliarity with lab material prior to attending lab, my lab partner and I failed to collect the RI results for the simple distillation until about halfway through the activity. Because of this, we came in to open laboratory hours on Friday to repeat activity two of the experiment, and recollected data for both simple and fractional distillation. When we repeated the experiment, I noticed that we were able to set up the distillation apparatus more efficiently and felt more confident in our skills. I now feel that I will be able to easily recreate experiments that involve distillation, which provides me with confidence as I approach the steam distillation experiment that is coming up in experiment #5.
If I could do this lab again differently, I would take the time to retest my RI values for my simple distillation procedure to recheck the noticeable outliers that I have on my graph.
Post Lab:
1. What would be the effect on the boiling point of a solution such as water if a non-volatile but soluble substance like salt was present? What if a non-volatile and insoluble substance like sand was present?
The presence of a soluble substance within water causes the boiling point of the water to increase. However, if a non-volatile substance is seen, the water will boil without a change to the boiling point but a precipitate will remain behind as a product of the boiling process.
2. Why would we not conduct distillations in a completely closed/sealed apparatus?
To prevent accidental shatter of the glass apparatus due to increased heat and associated pressure as the solution is heated.
3. How is fractional distillation as performed in the lab both the same and different from how it is performed at an oil refinery?
Both fractional distillation that is performed in a lab and fractional distillation performed in an oil refinery separate compounds based on their boiling points. This is accomplished through the selective heating and then later cooling of a selective part of a liquid. While this is often performed in labs, this process is also performed in oil refineries on a much larger scale with equipment that is more expensive and specialized for the distillation of oil to allow for maximized product collection.
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