049 Micro-Distillation Lab

Expt 049 -- Micro-Distillation Lab

A variety of plastic pipets can be cut up and joined together to make a very small and very quick distillation apparatus, complete with heating chamber, boiling chip, condensing tube with sleeve and collection bottle. A boiling hot water bath brings 2-3 mL of 30% ethanol solution to a boil in less than a minute. Successive distillate portions are collected and then tested for density and flammability.

Chemical Concepts

Chemical compounds may be separated or purified by physical properties.
Boiling points of chemical compounds depend on molar masses and intermolecular attractions. Consequently, boiling points are different for different compounds.
With fractional distillation, the separation is not 100% effective. Vapors of both volatile components distill across. The distillate, however, possesses a higher concentration of the more volatile component (alcohol) than the original mixture contained. The procedure may be repeated to concentrate the more volatile component.

Objective

Can you separate two liquid substances from a solution?

Safety

Use care in handling the alcohol. Alcohol is a flammable liquid. Keep alcohol away from flames.

Procedure

Construction of the Still:

Condenser:

Use a hot nail held with pliers to melt two holes in a super jumbo pipet - one on the top and one on the shoulder. Cut the stem off close to the bulb. Use a scissors to enlarge the hole at the top enough to slide over the stem you cut off. Slide the stem through the bulb with the stem away from the extra hole. Hot glue around the joint.
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Boiling Pot:

Use a super jumbo pipet for the boiling pot. Use a hot nail held with pliers to melt one hole on the shoulder of the bulb. Cut the stem off about 1 cm from the bulb. Then cut a 1 cm piece of tubing from the large straight end of the stem. Block off one end of this tube with a drop of hot glue.
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Collection Tubes:(Make 3)

Use a slightly smaller pipet for collection. Melt a hole in the shoulder of the pipet. Cut the stem off leaving about 1 cm.
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Assemble the parts:

Place a micro boiling chip (marble chip the size of a rice grain) into boiling pot. Use the "Y" tube to connect the boiling pot, condenser, and blocked-end tube. Insert the tip of the condenser into the hole in the shoulder of the collection tube. Push the bulb of a thermometer into the hole in the shoulder of the boiling pot, the fit should be snug and air tight.
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Distillation:

Remove the thermometer. Check to see if a boiling chip is in the pot. If not, add one. Use a thin-stem pipet to add cold tap water to the outer sleeve of the condenser. Use a second thin-stem pipet to add the alcohol solution to the boiling pot through the thermometer hole. Push the thermometer back into its hole. Support the apparatus by holding the thermometer. Dip the bottom of the boiling pot into the hot water bath. Observe the temperature, and the behavior of the solution. Note the temperature when boiling in the pot begins. Collect 6-8 drops of distillate in the collection bulb, then remove the collection bulbs, and replace it with an empty one. Note the temperature, then collect another 6-8 drops. Repeat this one more time with a third collection bulb, then remove the apparatus from the hot water bath and allow to cool. Number the collection bulbs 1, 2, and 3.

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To control the rate of the boiling and prevent "bumping" from heating too fast, lift the pot out of the hot water when it begins to boil rapidly. To keep the solution at a gentle boil, immerse the bottom again.

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Test each of the three distillates and the solution left in the pot to see how flammable they are. To test, place one drop on the table. Light with a flame. Record the flammability. Also, test one drop of pure ethanol and one drop of pure water.

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Test each of the three distillates and the solution left in the pot to see how dense they are. Add a drop of each to a container of mineral oil. Place the tip of the pipet under the surface of the oil and squeeze. Note whether the drop floats or sinks, and how quickly it does so. Also test pure water and pure ethanol. Record your observations.

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Variation:

Try distilling the distillate, to get an even higher concentration of ethanol. The flammability increases and the density decreases even more! Note: with some mixtures, successive fractional distillations produces distillates that approach 100% purity of the more volatile component. With water and ethanol, the best that can be obtained by distillation is a 95% ethanol solution, the azeotrope.

Questions

Rank each substance (pure water, pure ethanol, distillate #1, #2, and #3) in order of increasing flammability.
Rank each substance (pure water, pure ethanol, distillate #1, #2, and #3) in order of increasing density.
What happened to the boiling point of the solution during the extended distillation process?
1. Which of the three distillates possessed the highest ethanol concentration?
2. Which possessed the lowest?
3. What evidence supports these conclusions?
4. What explanation can you offer for why the distillates varied that way in their relative ethanol concentrations?
Explain how fractional distillation works.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 049 Micro-Distillation Lab

Watch the movies and answer the questions.

Curriculum-

Use this experiment when discussing changes of state or separation of organic compounds.

Activity-

Laboratory or Demonstration
The experiment works well as a laboratory for students. However, you may use it as a demonstration.

Safety-

Use care in handling the alcohol. Alcohol is a flammable liquid. There should be no open flames during the distillation process.
Dispense alcohol in small amounts to minimize the danger of fire.

Time-

Teacher Preparation: 10 minutes (45-55 minutes if you are assembling the distillation set-ups for the students)

Class Time: 25 minutes (45 minutes if they are assembling the distillation set-ups themselves)

Materials-

(Per group)

4 mL of 30/70 ethanol (v/v) -- (Mix 30 mL of ethanol and 70 mL of water. Add a few drops of food coloring.) Or use cough medicine which contains ethanol, or windshield wiper fluid which contains methanol.
2 super jumbo plastic pipets
3 graduated plastic pipets
2 thin-stem plastic pipets
1 Y-plastic connector (of a size that fits snugly into cut-off super jumbo pipet stem)
1 thermometer
permanent marker
scissors
1 hot glue gun with glue
1 nail and pliers to hold it
1 Bunsen burner(to heat nail)
1 600-mL beaker of water
hot plate (to heat hot water bath)

(Per class)

1 50 mL graduated cylinder (for the mineral oil)
50 mL or mineral oil (to test the density of the distillate.)
food coloring

Disposal-

Discard the upper and lower immiscible layers from the mineral oil. Store the rest for reuse.
Distillation set-ups can be re-used many times with occasional repairs and part replacement as needed.
Left-over solutions and collected distillates are safe to rinse down the sink with water.

Lab Hints-

If you have one distillation apparatus assembled as a model, students may make the distillation apparatus in the laboratory. Supervise use of the hot glue gun carefully.
To save time, have the distillation components already cut and ready to be assembled.
Although Bunsen burners are needed to heat the nails to melt the holes in the pipets, there should be no open flames during the distillation, the alcohol vapors produced are quite flammable. Use hot plates to heat the water baths.
With the boiling pot portion of the apparatus in the hot water bath, the collection bulb hangs over the side. Students should be careful not to allow the collection bulb to touch the edge of the hot plate, for it might melt a hole and allow the distillate to leak out.
The food coloring in the alcohol-water mixture prevents it from being mistaken for plain water. It also lets the student see how a nonvolatile solute, such as the dye, does not distill across at all. It also lets you see whether a group has boiled their solution too vigorously; if their collected distillate is colored, it means that some of the pot solution squirted across during rapid boiling.

Answers-

Q1. Rank each substance (pure water, pure ethanol, distillate #1, #2, and #3) in order of increasing flammability. A1. Water is the least flammable, then dist. #3, then #2, then #1, then pure ethanol is the most flammable.
Q2. Rank each substance (pure water, pure ethanol, distillate #1, #2, and #3) in order of increasing density. A2. Ethanol is the least dense, then dist. #1, then #2, then #3, then water is the most dense.
Q3. What happened to the boiling point of the solution during the extended distillation process? A3. The boiling point gradually increased during the distillation.
Q4. a) Which of the three distillates possessed the highest ethanol concentration? A4. a) Distillate #1 had the highest ethanol concentration
Q4. b) Which possessed the lowest? A4. b) Distillate #3 had the lowest
Q4. c) What evidence supports these conclusions? A4. c) The relatively high flammability and low density of distillate #1 supports this conclusion.
Q4. d) What explanation can you offer for why the distillates varied that way in their relative ethanol concentrations? A4. d) When the distillation began, the starting mixture was about 30% ethanol and the vapors that came across contained a high level of ethanol (maybe around 60%, which would thus make the first distillate around 60% ethanol). But as this continued, with more ethanol leaving the boiling pot than water, the solution left behind contained an even lower ethanol concentration. The boiling point therefore went up, and the vapors coming off contained a lower ethanol concentration than they originally did. Thus, the second distillate sample collected did not contain as high an ethanol concentration as the first (perhaps only 50%). The third distillate collected of course had an even lower ethanol concentration, and so forth.
Q5. Explain how fractional distillation works. A5. Assume you have a mixture of two liquids, A and B, in which A is more volatile than B. The vapors coming off this mixture are also a mixture, but one that has a higher concentration of A than did the original mixture -- the bigger the difference in volatilities, the bigger this increase in A's concentration. If the vapors are allowed to pass into a separate container and are condensed there back into a liquid mixture (known as the distillate), that mixture's composition is the same as that of the vapor: rich in component A. This is the principle behind fractional distillation. Since higher temperature's cause greater evaporation rates, distillations are usually performed at high temperatures (the highest obtainable at 1 atm, is of course the boiling point of the mixture). This generates a large quantity of vapors, and therefore allows a high rate of distillate production. Note: this primary distillate may in turn be heated, and the vapors separated, cooled and collected. The secondary distillate produced contains an even higher concentration of A. This may be repeated again and again to maximize the concentration of A.

Key Words 1-

boiling point, condensation, liquid, gas, distillation, separation