Name:
Lab Partner(s):
Per:
Date done:
Lab: Separation by Distillation
Introduction
You know that you can often separate substances by taking advantage of their different physical properties. One
physical property commonly used to separate liquids is their density. However, density differences will work
only if substances are insoluble (do not dissolve) in each other, which is not the case with petroleum; its
components are soluble (can dissolve) in each other. Another physical property chemists often use to separate
substances is boiling point. The separation of liquid substances according to their differing boiling points is
called distillation.
As you heat a liquid mixture containing two components, the component with the lower boiling point will
vaporize first and leave the distillation flask. That component will then condense back to a liquid as it passes
through a condenser. Each condensed liquid substance, called a distillate, can be collected
In this activity, you will perform a distillation of Cherry Coke. You will separate the Cherry Coke into three
fractions: fraction 1, the initial distillate (the first 20 mL that distill); fraction 2, the second 20 mL that distill;
and fraction 3, the residue.
Your task is to figure out where three Cherry Coke components end up: the cherry aroma, the sugar, and the
phosphoric acid. You will be able to detect the cherry aroma with your nose. You will perform a Benedict’s
Test to determine whether the sugar is in the distillate or the residue. You will check the pH as a test for
phosphoric acid.
Procedure
1. Check to be sure your apparatus is assembled as in the drawing above. Obtain two 50 or 100 mL beakers,
label them 1 and 2.
2. Check to make sure there are ~5 boiling chips in the flask. Boiling chips are little chips of porous rock
which help ensure smooth boiling without “bumping”. Pour 100 mL of Cherry Coke into the flask.
3. Test the pH of Cherry Coke and compare with the pH of tap water. Record, along with your observations of
the Cherry Coke appearance.
4. Reconnect the flask to the condenser, making sure all connections are tight and will not leak. Be careful not
to put too much stress on the glass pieces; very carefully adjust the clamps if necessary. Position a
graduated cylinder at the outlet of the condenser so it will catch the distillate.
5. Slowly turn on the water to the condenser. Turn on the hot plate to 550 deg Celsius and start gently heating
the flask.
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6. Starting when the first drop of distillate enters the graduated cylinder, every minute, record the time,
temperature, and cumulative volume of distillate collected. After you collect 20 mL of distillate, pour it into
Beaker 1 and reposition the graduated cylinder under the outlet. After you collect another 10 mL of
distillate (30 ml of total distillate) then turn off the hot plate and unplug it, collect another 10 ml (about 40
ml distillate) then pour it into Beaker 2.
7. Test the pH of Fractions 1, 2, and the residue when it has cooled, record their appearance, and check for
cherry aroma by wafting the air above each beaker toward your nose.
8. Benedict’s Test for Sugar. Heat about 100 mL of water to about 80oC. Label five test tubes 1-5. Following
Table 2, mix the appropriate amounts of solution in each tube. Tube #1 contains Fraction 1. Tube #2
contains Fraction 2. Tube #3 contains the residue (stuff left in the pot). Tube #4 is your reference solution
– it contains Karo syrup, which contains fructose, like the high fructose corn syrup sweetener in Cherry
Coke. Tube #5 is your control—it contains distilled water and should give a negative test for sugar.
9. Place the five test tubes in a hot water bath at 85-100°C for about 3-5 minutes, or until your reference, Tube
#4, forms a red-brown precipitate. Record the results of your Benedict’s Test.
Data
Before Distillation
pH
Appearance
Cherry Coke
Table 1. Distillation Data
Elapsed
time, min
Temp,
°C
Cumulative
volume (mL)
Elapsed
time,
min
0
14
1
15
2
16
3
17
4
18
5
19
6
20
7
21
8
22
9
23
10
24
11
25
12
26
13
27
Temp, °C
Cumulative
volume (mL
2
After Distillation:
pH
Appearance
Presence of cherry
aroma (Y/N)
Fraction 1
Fraction 2
Fraction 3 (residue)
Table 2. Benedict’s Test for Sugar
Tube #
Solution
drops of
Benedict’s
soln
1
5 drops Fraction 1
20
2
5 drops Fraction 2
20
3
5 drops Residue
20
4
5 drops Karo syrup solution
(reference)
20
5
5 drops distilled water
(control)
20
Formation of red-brown precipitate?
(Y/N)
Questions. USE FULL SENTENCES
1. What is the purpose of the boiling chips?
2. Why is the condenser called a condenser?
3. What do you think is the major ingredient in Fractions 1 and 2? What observation supports this conclusion?
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4. What is one physical test (other than tasting) you could perform to confirm that Fraction 1 and 2 are mostly
water?
5. Where did most of the cherry aroma end up?
6. Where did the sugar (fructose) end up? How do you know?
7. Where did the phosphoric acid end up? How do you know?
8. What physical property is used in a distillation to separate substances in a mixture?
9. Cherry aroma comes mostly from a compound called benzaldehyde. Judging from where the cherry aroma
and sugar each showed up at the end of the distillation, what can you conclude about the relative boiling
points of benzaldehyde and sugar? Explain.
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