CHEM230L_EXP3_Distllation

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Jan 9, 2024

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CHEM 230L: Organic Chemistry I Lab Chapman University Experiment 3: Purification and Identification of Organic Liquids by Simple and Fractional Distillation Intended Learning Outcomes By completing this lab, we will: • Understand the relationship between intermolecular forces (IMFs) and how they affect the boiling point of liquids. • Understand how the different boiling points of liquids can be utilized in distillation. • Learn how to purify liquid organic compounds through the distillation of mixtures of miscible liquids. • Be able to identify unknown compounds by boiling point. Introduction Distillation is a common purification technique that can be used to separate a mixture of liquids. Moreover, distillation allows for the separation of mixtures of miscible liquids that would otherwise be inseparable. Distillation can also help to potentially identify unknown liquids based on boiling points. The differing boiling points of liquids are employed during distillation. A mixture of liquids is heated and eventually the different components will begin to boil. The liquid with the lowest boiling point will boil first, followed by the liquid with the next lowest boiling point, and so forth. When these individual compounds are vaporized and escape from the liquid mixture, they can be condensed and collected. By monitoring the temperature of the vapor from the distillation, one can determine when different compounds are vaporizing. By changing out a collection flask once the temperature changes, the pure compounds from the mixture can be collected separately from one another. In this lab, you will explore two different types of distillation, simple and fractional. Simple distillation is the most basic distillation technique and can only separate miscible liquids if they have significantly different boiling points. Fractional distillation can be used to more effectively separate compounds with close boiling points. Vacuum distillation and steam distillation are examples of other distillation techniques. Steam distillation will be explored during a later lab. Pre-Lab Reading The reading below needs to be completed before the start of lab. 1. Lab textbook (Pavia, 6 th edition): Technique 14 – Simple Distillation: pages 756-767. Lab textbook (Pavia, 6 th edition): Technique 15 – Fractional Distillation: pages 768-784. 2. Lab textbook (Pavia, 6 th edition): Experiment 8 – Simple and Fractional Distillation: page 58 – 65. 3. The procedure for the lab experiment that will be done in lab below.

CHEM 230L: Organic Chemistry I Lab Chapman University Pre-Lab Assignment (15 points) Answer the following questions: 1. A distillation is done on a mixture that contains acetone, isopropyl alcohol, and benzene. Look up the boiling points for these compounds, list them, and determine the order in which these compounds would be collected in a distillation. Explain your reasoning. (4 pts.) Acetone: 56 C Isopropyl Alcohol: 82.5 C Benzene: 80.1 C Acetone would be collected first in a distillation since it has the lowest boiling point, then benzene, then isopropyl alcohol. The compounds with the lowest boiling points will evaporate first in a distillation. 2. What is the difference between a simple distillation apparatus and a fractional distillation apparatus? (2 pts.) Simple distillation is implemented when there is a large difference in the boiling points of our two compounds, and it separates relatively pure compounds. Fractional distillation is implemented when the boiling points of the two compounds are relatively close, and it yields a larger separation than a simple distillation. In terms of the apparatus, the fractional distillation includes a fractioning column, in which it is packed with some sort of filtering material such as a steel sponge. This is in place to have continuous vaporization- condensation cycles which is how this technique yields more pure substances compared to the simple distillation method. 3. Explain why fractional distillation allows for a more effective and thorough separation of liquids with close boiling point as compared to simple distillation. (4 pts.) Although it may take longer than simple distillation, the slow process of repeated vaporization-condensation cycles within the fractional column enables the vapor to be enriched in an increasing concentration of the compound with the lower boiling point. As these cycles repeat, the compound with the lower boiling point then emerges from the top and yields a significantly purer compound compared to if it was distilled in a simple distillation. 4. In a fractional distillation of a two-component mixture, the temperature of the two-component vapor mixture decreases gradually as it rises through a fractional distillation column. Explain this observation. Use a graph or diagram in your explanation. (5 pts.) The temperature of the two-component vapor mixture decreases gradually as it rises because the packing material, such as the stainless-steel sponge, facilitates vapor-liquid equilibrium by providing a surface area for the evaporated compounds to interact more, but it also provides a temperature gradient in which higher temperatures are at the bottom and lower temperatures are at the top. In the drawing below, it shows the blue compound (greater boiling point) as well as the red compound (lower boiling point) separating across a surface, which the packing material imposes many surfaces for greater separation.

CHEM 230L: Organic Chemistry I Lab Chapman University Procedure Simple Distillation 1. Set up the distillation apparatus as shown below (from page 61 of the lab textbook) but instead use a 25-mL round bottom flask equipped with a magnetic stir-bar and use 25- or 50-mL graduated cylinder to collect distillate. Be sure you have the thermometer in the correct position and that you have used an O-ring in the thermometer adapter assembly.

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CHEM 230L: Organic Chemistry I Lab Chapman University 2. Obtain an unknown sample and record the unknown sample number. Add 15 mL of the unknown sample solution into the round bottomed flask. The unknowns are mixtures of two of the following compounds: Hexane, Cyclohexane, Heptane, Toluene. 3. Lower the apparatus into a heating block on a hotplate stirrer. Connect a water hose from the cold waterspout in the hood to the bottom inlet of the condensing tube. Connect a water hose to the top inlet of the condensing tube and place the other end into the sink in the hood. Turn the water on slowly and make sure it starts to flow into the sink. 4. Insulate the distillation system with paper towels and tape ( Caution: don’t let the paper towel touch the surface of the hot plate as it can burn the paper towel). 5. Adjust the hotplate temperature to about 140 o C and commence stirring of the solution. Once the solution begins to boil, adjust the temperature of the hot plate up or down so that distillation rate is around one drop of distillate into the graduated cylinder every 2 to 3 seconds. 6. Record the temperature of the distillation by reading the thermometer for every mL of distillate collected in the graduated cylinder. Be sure to record what volume corresponds to what temperature as well. Collect the distillate until there is no liquid left in the round bottomed flask. At this point turn off the heat and allow the apparatus to cool down. Fractional Distillation

CHEM 230L: Organic Chemistry I Lab Chapman University 1. Once the distillation apparatus has cooled down, assemble a fractional distillation apparatus by inserting a fractionating column in between the distillation head and round-bottomed flask. 2. Add 15-mL of the same unknown used in the simple distillation to the round-bottomed flask. Carry out a distillation using the same procedure as above and collect data as you did with the simple distillation. Post-Lab Assignment (40 points) Data Analysis 1. Enter the number of your unknown sample used (1pt.) __________ 2. Show your data by listing the volume of distillate collected and the corresponding temperature for the simple distillation. (3 pts.) 3. Generate a graph (hand drawn or excel) showing temperature of the distillation vapor on the y-axis and volume collected on the x-axis for the simple distillation. Connect the data points with a smooth line. (4 pts.) 4. Show your data by listing the volume of distillate collected and the corresponding temperature for the fractional distillation. (3 pts.) 5. Generate a graph (hand drawn or excel) showing temperature of the distillation vapor on the y-axis and volume collected on the x-axis for the fractional distillation. Connect the data points with a smooth line. (4 pts.) 6. Based off the temperatures observed from the distillation, what is the identity of the two compounds (from Hexane, Cyclohexane, Heptane, Toluene) in your unknown mixture? Explain your reasoning (6 pts.) 7. Based off the volumes and temperatures observed from the distillation, what is the ratio of the two compounds in your unknown mixture? Explain your reasoning (4 pts.) 8. Which of the distillations was more useful in determining the identity and ratio of the compounds in your unknown mixture? (2 pts.) 9. Overall, comment on the effectiveness of the distillations you performed. Did both work at separating mixture of liquids to the same extent? Were you able to easily identify the compounds in your mixture and their ratio? , etc. (3 pts.)

CHEM 230L: Organic Chemistry I Lab Chapman University Conceptual Question: 1. In a fractional distillation, the length of the column and materials used as the packing material can help increase the ability of the distillation to separate compounds. What needs to be done to the length of the column and what needs to be used as packing material to see this benefit? (3 pts.) 2. In a perfect or even very good distillation system, a small dip in temperature will be observed after all the first liquid has been collected and before the temperature begins to rise again. Explain this observation. (3 pts.) 3. Find two additional packing materials that can be used for the fractionating column besides steel wool (4 pts.)

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