Objective Statement: The objective of this lab is to learn how to purify compounds by using the differences in boiling points to separate two compounds through the process of distillation. By learning about the effectiveness of distillation and the process of acquiring and accessing purity by a refraction curve of data collected from a refractive index. Along with comparing the effectiveness of two distillation processes; simple distillation and fractional distillation.
Embedded Files
Compounds of Study:
Cyclohexane
Cyclohexane
C6H12
Boiling Point: 78 degrees Celsius
Molar Mass: 84.6g/mol
Toluene
Toluene
C6H5CH3
Boiling Point: 111 degrees Celsius
Molar Mass: 92.4g/mol
Pre-Lab Questions:
1. What is the property of refraction? In other words, when you are testing the refractive index, what are you testing for?
Refractive index measurements check the purity and concentrations of a liquid.
2. What kinds of compounds are best separated by distillation?
Liquids with significantly different boiling points.
3. Describe fractional distillation in your own words.
Vaporizing and collecting the condensed fractions of compounds in a liquid mixture by separating the compounds through the difference of boiling points.
5. Why is it important not to overheat your flask during distillation?
Higher unwanted quantities of the higher boiling point compound will condense in fractions way before it is supposed to which will impurify your solution.
6. Why is it important to use grease in the glass joints? What happens if you use too much? If you use too little?
To ensure a proper seal between the glass components. Too much can clog the glassware and effective vaporization effectiveness. Too little will result in a not proper seal and vapor will escape.
7. Why is it important to have cold water flowing through the condenser?
To cool vapor and ensure effective condensing of the solution vapor.
8. Describe an azeotropic mixture and the distillation of an azeotropic mixture.
An azeotropic mixture has the same concentration of vapor and fluid phases. To distill an azeotropic mixture, the addition of a material separation agent that has the ability to change the molecular interactions between components of the azeotrope needs to be added to purify a mixture.
9. When is steam distillation used for purification?
To separate volatile organic compounds from nonvolatile inorganic salts.
10. When is vacuum distillation used for purification?
Only possible way to distill compounds with boiling points over 200 degrees Celsius
11. What is the purpose of activity #1 for this lab? Why are you creating a calibration curve?
The purpose of activity one is to understand the effectiveness of distillation in determining the purity of a compound. A calibration curve helps to determine the concentration of a sample with an unknown concentration at stages.
12. What material should distill first, cyclohexane or toluene? How did you come to this conclusion?
Cyclohexane should be distilled first. Cyclohexane has a much lower boiling point than toluene; 78 degrees Celsius compared to 111 degrees Celsius. This means that from 78-110 degrees Celsius, only Cyclohexane will be evaporated out of the mixture to be distilled.
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?
The difference between these activities is that you will compare your results from your distillation technique in activity #2 to the other process from another student in activity #3 with graphs and charts. Activity #3 should be more effective in separating cyclohexane and toluene.
Procedures:
Activity #1:
Acquired 2 concentrations of cyclohexane and toluene: One 75% toluene and 25% cyclohexane. And another 100% toluene and 0% cyclohexane.
Mixed solutions in pipette
Added a few drops into the RI basin
Recorded numbers displayed on RI on whiteboard (see results below)
Compared answers from classmates and wrote down average RIs to create a calibration curve. (see results below)
Activity #2
Set up a simple distillation apparatus
Insulated heating cylinder with tin foil. Speed up the evaporation process since the vapor has to travel up the glass tube.
Acquired 60 mL of 1:1 cyclohexane/toluene mixture and put it into a round flask with boiling chips, the flask should be 50%-75% of the way filled.
Attached the heating mantle with appropriate fitting and set the rheostat to 25.
Heated the mixture to a boil
Every 3 mL of acquired distillate, recorded the distillation temperature and transferred the distillate into a separate test tube to record the Refraction Index of the fraction (see results below).
After 30 minutes of light boiling, increased the heat setting to around 32. The distillate was not being produced at the desired rate.
After an hour of light boiling, increased the heat setting to 35. To account for the concentration of cyclohexane decreasing as more of the compound has been boiled out.
Collected 12 fractions of distillate and removed the heat source.
Results:
Activity 1:
Below are the collected RI values of the different concentrations of cyclohexane collected by the class. The average of the two values collected were the numbers used to graph the data on the chart to the right of the table. Along with a calibration curve of -.00007x + 1.4927
Activity 2:
Simple distillation data chart and graphs of comparison.
Activity 3:
Shared fractional distillation data chart and graphs of comparison.
Conclusions
Both the simple and fractional distillation processes yielded similar data. As the ml of Distillate increased, higher temperatures were recorded to boil out the distillate. Along with similar trends in the percent of Cyclohexane present within the distillate extracted. Both processes recorded that as volume increased, the distillate had a lower concentration of cyclohexane. Both sets of data collected from the two distillation processes showed the expected results that the longer distillation took place, less and less cyclohexane would be evaporated out of the solution, and in turn, caused the temperature of the solution to increase as the solution became more concentrated with toluene and its higher boiling point. Both these points align with the purity of the fractions extracted. From Activity #1, we can see higher concentrations of cyclohexane would have lower RI values. This means that the % cyclohexane graphs also agree with the RI values of the data collected as the higher concentrations of cyclohexane will have the lower RI values. And despite having far less fractional data collection, the fractional distillation process provided more accurate and effective fractions as we can compare the data collected in the lab to the calibration curve of the collected class to see that the fractional data aligns more accurately when comparing the data collected in the simple distillation process.
Reflections:
During this lab, I learned about the importance of understanding the boiling point, concentration, and practice techniques of the lab and how understanding that information can help me to check and comprehensively check the data I collect. This idea helped me to properly be on track during my simple distillation process to ensure effective and efficient results. However, one thing I would do differently in the lab is to make sure that I ensure proper boiling and heating containment as the major hiccup that I experienced was that I took too long to heat my solution for distillation. This resulted in me only acquiring 12 fractions, a little lower than the expected fraction results of the lab.
Post Lab Questions:
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 addition of a substance like salt will decrease the liquid's vapor pressure and increase boiling point. A liquid will boil when its vapor pressure is equal to the atmospheric pressure, so as vapor pressure lowers, higher temperatures are required to boil the water. A non-volatile and insoluble substance like sand will not affect the temperature of the vapor pressure of water because it does not mix or dissolve into a solution.
2. Why would we not conduct distillations in a completely closed/sealed apparatus?
We will not conduct distillations in sealed apparatuses because distillation changes the vapor pressure of a liquid when heating. Meaning the sealed apparatus will build up pressure to the point of explosion.
3. How is fractional distillation as performed in the lab both the same and different from how it is performed at an oil refinery? You will need to look up information on the web on how oil fractions are separated. If you use Google search, I suggest choosing images and then selecting a website with a nice visual image.
The similarity of the fractional distillation performed in the lab, and the distillation performed in an oil refinery is the process of distillation itself; using various differences in components boiling points to extract specific hydrocarbons. However, distillation performed in oil refineries is performed by heating the entire solution at the highest boiling point of one hydrocarbon, and as the vapor proceeds through a massive collection column, temperature decreases and various hydrocarbons condense at different stages vertically through the column. This is different from how we boiled to a specific temp, just for cyclohexane, and then cooled the steam through the water to condense the cyclohexane for extraction,
Page updated
Report abuse