lab 2

Experiment 2: Simple and Fractional Distillation -

Determination of Solution Composition

This week, we will be using a technique known as distillation to separate a solution of two unknown, miscible liquids. Separation will be achieved based on the difference in boiling points of the two liquids and using a complex glassware apparatus. The following questions will be asked and answered during the course of the experiment:

• What are the identities of your two miscible liquids?

• What is your specific solution composition (ratio of liquids)?

• Which form of distillation (simple/fractional) is the more efficient in regards to your current experiment?

Additional background information concerning both distillation and boiling point determination is provided in the experimental theory section of this manual.

New Techniques:

Distillation (simple/fractional) (experimental theory section page 43) Boiling Point Determination (experimental theory section page 43)

Table of Reagents:

Gather all relevant physical data for the following compounds:

Methanol (structure, MW, BP, densities) Ethanol (structure, MW, BP, densities) Water (structure, MW, BP, densities)

IMPORTANT - Ethanol and water form an azeotrope when mixed in solution. Refer to page 49 of the

In today's experiment you will be using this data to determine the identity of your unknown liquids and the ratio of each component in your mixture.

Safety:

You will be working with boiling liquids and handling hot glassware. Caution must be exercised at all times. Be careful to never heat a sealed vessel, and always make certain to add a boiling chip to any liquid before heating it. Safety glasses and lab gloves are to be worn at all times. Methanol and ethanol are highly flammable. Avoid sparks, flames and hot surfaces. Both liquids are also toxic and care must be taken to avoid breathing any fumes. Make sure that your appararus has fully cooled prior to dismantling it. Any vapor or liquid exposure should be reported to your TA immediately. Dispose of all liquid waste in the appropriately labeled bottle in the lab hood.

Setting Up the Apparatus:

The most challenging aspect of any distillation experiment is setting up the apparatus. The appropriate glassware setup for a simple distillation is illustrated in Figure 1. A slightly modified version of this apparatus will then be used for the fractional distillation component of the lab (see Figure 2).

Glassware/Equipment Checklist:

Heating Mantle: This is the heat source for the distillation apparatus. Make sure that you choose a mantle of appropriate size so that the heating will be uniformly distributed around the flask during the course of the experiment. The heating mantle will be suspended above the bench top by an iron ring to bring it into contact with the raised distillation flask. If the flask begins to boil too aggressively during

the course of the experiment, simply lower the ring, removing the mantle from contact with the

apparatus. Realize that simply turning off a heating element does not instantly cool it to room

temperature. You must remove it from contact with the flask in order to quell any over boiling. Make sure that the mantle is paired with a Variac voltage controller. Do not plug the heating mantle directly

into an electrical outlet. This is extremely dangerous and can cause the mantle to burn out or spark, resulting in a fire. You will be using the Variac to determine the rate of heating for your distillation. Choose a setting that will allow you to collect roughly 1-2 mL of distillate per minute.

Round-Bottomed Flask (Distillation Flask): Choose a flask of appropriate size for your experiment.

The general rule is never to fill your distillation flask less than one third or more than two thirds full.

Too much headspace in a flask can lead to a loss of distillate during the course of the experiment. Too

little headspace can result in foaming or over boiling of the solution into the still head which leads to

poor separation. The flask should be positioned several inches above the bench top (specific heights

will vary). Securely clamp the neck of the flask to your ring stand. Proper clamping of your apparatus

is crucial and can help avoid costly accidents. Don't forget to carefully secure your glassware at each

stage of the build. Place several boiling chips into your distillation flask along with the binary solution

you are attempting to separate. The use of boiling chips is essential and they must be added prior to adding heat to the system. In much the same way that seed crystals provide points a nucleation for

crystal growth in a recrystallization, boiling chips provide points of vaporization for a boiling liquid.

This will help ensure that the solution boils smoothly and uniformly during the course of the experiment.

If boiling chips are not used, uneven heating can result in the formation of"hot spots" which can cause

the solution to bump or splash into the still head. Bumping results when a heated liquid releases a

sudden surge of vaporized gas rather than allowing the gradual formation of vapor from multiple

locations within the fluid. This will cause the solution to chum aggressively and must be avoided at all costs.

Distillation Head (Still Head) and Thermometer: Place the bottom joint of the still head securely in the neck of your round-bottomed flask. With the flask clamped at the neck joint, the weight of the still head will be carried by the ring stand. Insert your thermometer into the upper arm of the still head using either the built-in, tapered glass joint or a separate thermometer adaptor (provided by your TA) to hold it in place. Ask your TA for help if you are unsure as to which method will work best for your apparatus. The thermometer must be positioned correctly within the still head in order for accurate readings to be made during the course of the experiment. The bulb of the thermometer must rest just below the side

arm of the still head. If the bulb is positioned too high, the readings will be abnormally low as much of the vapor will condense into the sidearm before reaching the thermometer. If the bulb is positioned too low, the readings will be abnormally high due to close proximity to the boiling flask/heating element. The joints on your glassware are specifically designed for a tight fit. Apply a small amount of vacuum grease to the ground glass joints as you assemble the apparatus to ensure that it is properly sealed and no vapors will escape during the course of the experiment. Be careful however, using too much grease can potentially contaminate your solution. The proper greasing technique will be demonstrated during the prelab lecture. Remember, glass expands when heated and contracts when cooled. The grease seals the gaps as expansion occurs and prevents fusion as glassware contracts.

Condenser (24/40): The condenser is attached to the side arm of your distillation head. This is a heavy. piece of glassware and cannot be supported simply by the clamp positioned at the joint of your distillation flask and still head. A second ring stand must be added with a clamp placed halfway down

the body of the condenser to handle the extra weight of the apparatus. Two latex hoses are then attached to the tapered inlets and outlets on the sides of the condenser (see Figure 1). The hose leading you’re your water source (faucet) must be connected at the lower inlet and the hose leading to the sink/trough must

be connected at the upper outlet. If the hoses are not attached at the appropriate points, the outer jacket

of the condenser will not fill once the water is turned on and the vapors gathering in the distillation head'

will not properly condense to be gathered in the catch flask/cylinder. Make sure that you have attached

the hoses securely. Having a hose come loose during the experiment is a common problem and can lead. to soaked lab notebooks and Jab partners. Do not use too high a water pressure in your condenser.

Check the flow of water into the sink/trough from your outlet hose. As long as the condenser jacket is

filled, a steady trickle of water is all that is required.

you will be using a short stem funnel placed in the neck of your 10 mL graduated cylinder to capture your distillate as it condenses. The cylinder and funnel will be placed underneath the open end of your condenser. Adjust the height your apparatus so that the distillate does not have far to fall before being collected. The use of the 10

mL cylinder allows for a more accurate measurement of collected liquid than the 100 mL version. As you fill the cylinder, you may empty it into a flask in between drops so that your data gathering may proceed uninterrupted. As you collect the distillate, make sure that you keep an eye on your boiling flask. Never boil your flask to dryness. Always leave several milliliters of solution in the flask at the end of the experiment. A dry flask is prone to calamity (cracking) and must be avoided.

General Experimental Guidelines:

Students will be working in groups of four this week (two groups of two). One group will be responsible for the simple distillation of an unknown binary solution, while the other will perform the fractional distillation of the same unknown mixture. Make sure that you write down the sample number that your groups used for the experiment. This is critical for your successful completion of the lab. In addition, make sure that you record all of your volume and temperature measurements .. You will be required to graph this data for both distillation methods in your postlab write-up. Work together during the course of the experiment. Both groups are equally responsible for the data from both distillation

methods.

Experimental Procedure: Simple Distillation

One group will carry out the simple distillation of an unknown binary solution. Place 21 mL of the solution into a 50 mL round bottom flask along with several boiling chips.

Construct a simple distillation apparatus and begin boiling your solution. Use the Variac voltage

controller attached to your heating mantle to regulate the heating of your distillation flask so that you

collecting approximately 1-2 mL of distillate per minute. Do not simply tum the dial to "10" from the

outset. i:ushing a di tillation will result in P?or sep ation d a long r stay in the laboratory. Slow

steady wms the race m the end. As the solution begms to boll, you will be able to follow the progress of the vapor as it moves up into the still head, from there into the condenser, and finally into the catch flask/cylinder. Record the temperature of the first drop of distillate collected and then the temperature of each milliliter collected during the course of the experiment. You are not required to collect all 2] mL of solution in your receiving cylinder. Obviously this would result in a dry boiling flask and that

must be avoided. Instead collect 18 mL of distillate (19 data points) and then remove the boiling flask from the heating mantle in order to begin cooling your apparatus to room temperature. Make sure that your glassware has cooled completely before dismantling the system. Remember that methanol vapors are toxic and must be avoided.

Experimental Procedure: Fractional Distillation

The second group will carry out the fractional distillation of the same unknown binary solution. Place 21 mL of fresh solution into a 50 mL round bottom flask along with several boiling chips. Construct a fractional distillation apparatus and begin boiling your solution. A fractional distillation apparatus is

identical to a simple distillation serup with one exception: a fractionating column packed with steel wooJ

is added in between the boiling flask and the distillation head (see Figure 2). Wrap this column in tin

foil to help avoid excessive heat loss as the vapor moves into the distillation head. Use the Variac

voltage controller attached to your heating mantle to regulate the heating of your distillation flask so that you are collecting approximately 1-2 mL of distillate per minute. Just as you did with the simple distillation, Record the temperature of the first drop of distillate collected and then the temperature of

each milliliter collected during the course of the experiment. Collect 18 mL of distillate (19 data points) and then remove the boiling flask from the heating mantle in order to begin cooling your apparatus to room temperature. Make sure that your glassware has cooled completely before dismantling the system. Remember that methanol vapors are toxic and must be avoided.
### General Experimental Guidelines

1.
- Students will work in groups of four, divided into two smaller groups of two. 
- One group will be responsible for the simple distillation of an unknown binary solution, while the other group will perform the fractional distillation of the same mixture.
- Record the sample number used for the experiment, as it is crucial for successful completion.
- Both groups will share responsibility for recording all volume and temperature measurements. This data will be used for post-lab graphs.



2.
- Place **21 mL** of the unknown binary solution into a **50 mL** round-bottom flask, adding several boiling chips to facilitate smooth boiling.
- Construct the simple distillation apparatus using the proper glassware and equipment.
- Connect the Variac voltage controller to the heating mantle to regulate the temperature, ensuring that 1-2 mL of distillate is collected per minute. 
- Adjust the dial carefully; do not set it to full power immediately to avoid poor separation and lengthy lab time.

3. **Monitoring Distillation**: 
- Once boiling begins, monitor the vapor's progress as it travels through the still head, condenser, and into the catch flask/cylinder.
- Record the temperature at which the first drop of distillate is collected, as well as the temperature for each subsequent milliliter collected.
- Collect **18 mL** of distillate (totaling **19 data points**) but do not allow the boiling flask to run dry during the process. This could lead to cracking or other glassware failure.
- After collection, remove the boiling flask from the heating mantle to cool the apparatus to room temperature.
- Ensure that all glassware has cooled completely before dismantling the system. 
- Caution is warranted, as methanol vapors are toxic; avoid exposure.

### Experimental Procedure: Fractional Distillation

4. **Preparation of the Fractional Distillation**: 
- In the second group, **21 mL** of fresh unknown binary solution is placed into a **50 mL** round-bottom flask with several boiling chips.
- Construct the fractional distillation apparatus, ensuring to include a fractionating column packed with steel wool between the boiling flask and distillation head. 
- Wrap the fractionating column in tin foil to minimize heat loss as vapor ascends toward the distillation head.
- Use a Variac voltage controller with the heating mantle to maintain a collection rate of approximately **1-2 mL** of distillate per minute, just as was done in simple distillation.

5. **Monitoring Distillation**: 
- Record the temperature of the first drop of distillate collected, along with temperatures for each milliliter collected during the process. 
- Collect **18 mL** of distillate (totaling **19 data points**) and remove the boiling flask from the heating mantle to cool to room temperature post-collection.
- Confirm that all glassware has cooled fully before disassembling the apparatus.
- Remain vigilant regarding methanol vapors, taking all necessary precautions to prevent exposure.

Discussion/Conclusion:

In your results section, prepare two detailed graphs (fractional data and simple data) comparing the temperature vs. volume measurements that you recorded during lab this week. Use these graphs to estimate the boiling points of the two miscible liquids in your original solution. Using these boiling point estimates, clearly identify the components of your unknown solution from the table of reagents. You must also use your data to estimate the ratio of the two components in your binary mixture.

Provide all data comparisons and state your reasoning in clear and concise terms. Which of the two methods provided a more efficient means of component separation? Why/how? Remember: restating the procedure is discouraged unless it is used to explain an error in data collection.

Student Name: TA Name:

Simple and Fractional Distillation Data Sheet

Unknown Binary Mixture Code: �----------

Exact starting volume of unknown solution: _

Simple Distillation (Temperature):

First drop: _

Fractional Distillation (Temperature):

First drop: _

***Post lab questions are located on ELC***