Name:
Period:
Teacher:
Date:
Paper Chromatography to Separate Mixtures
Objectives:
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Describe how chromatography works and what happens during this process to kool-aid
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Explain why being able to separate solutions into their components is important to environmental engineering and
water quality.
Materials:
1 piece of filter paper
small plastic beaker
scissors
4 different concentrated kool-aid
samples
metric ruler
water
pen and pencil provided by the
student
3 toothpicks
1 large beaker - at least 400 mL
Chromatography is used to separate mixtures of substances into their components to test if they are pure or a
mixture. There is a stationary phase (the paper) and a mobile phase (the liquid solvent). The mobile phase flows through
the stationary phase and carries the components of the mixture with it. Different components travel at different rates.
·
Different inks have different properties, such as how much they can be dissolved in solvents. When you place
chromatography paper into a solvent, the solvent begins to move up the paper. As the solvent rises, it dissolves the ink on
the paper and separates the ink into its components. The farther the ink travels, the better dissolved it is in the solvent.
Each component will have a specific retention factor, Rf value.
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Name:
Period:
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Procedure - work in pairs
1) Carefully fill a plastic beaker half full of water. Remember you must first turn on the water and adjust the
pressure before placing the beaker under the faucet!!
2.) Fill the large glass beaker so the height of the water is 1 cm.
3.) Obtain one sheet of chromatography paper. Use a pencil to draw a horizontal line 2 cm from the bottom of the
paper. Then add sample numbers 1-4. It is important that this is done in PENCIL.
4) In the center of each lane, on your pencil
line, place a dot of concentrated kool aid using a
toothpick. Apply the kool-aid 3 times to ensure the
sample is concentrated enough for our separation
experiment.
5) Fold the chromatography paper in half
vertically so it can stand up on its own. Carefully insert
the chromatography paper into the beaker dot end
down. The paper must be touching the solvent BUT
the dot can not be touching the solvent. If possible it
should not be touching the wall of the beaker.
6) Allow the beaker to remain undisturbed for
10 minutes or the solvent moves ¾ up the paper.
7) Carefully remove the chromatograph from
the beaker without spilling any solvent (water). Remove the
paper from the beaker and immediately use a pencil to mark
a line where the solvent stopped moving.
8.) Observe what colors were produced by the
migration of pigments by the solvent and record this on your
data table.
9.) Using a metric ruler, measure the distance the
solvent traveled from the colored dot. This means measure
from the dot to the pencil line. Record this value in your
data table under solvent distance.
10) Calculate the Rf values for each
color and record these Rf values on
the data table. (Rf= distance solute
moved/distance solvent moved)
11.) Empty your beaker down the
drain with lots of water. Take a
photo of your chromatogram next to
a metric ruler with the zero at the
bottom pencil line, then recycle the
filter paper.
2
Name:
Period:
Teacher:
Date:
Pre-Lab Question:
Dyes in foods appear to be composed of a single dye particle. In actual fact, food coloring is a
homogeneous mixture of different dyes. Grape kool-aid gets its color from a mixture of two different
dye compounds. Which particle diagram best shows a mixture of blue and red dye particles? We
can separate the different color dyes into their component colours by a method called
chromatography.
Which particle diagram above best illustrates the composition of dye?
Reasoning:
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Name:
Period:
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Date:
Data for Water Solvent
Observations:
Kool Aid Flavor
Solvent Distance
Color Distance (write each color in the box)
Color:______________
Color:______________
Color:______________
Distance traveled: ____
Distance traveled: ____
Distance traveled: ____
Rf: ________________
Rf: ________________
Rf: ________________
Color:______________
Color:______________
Color:______________
Distance traveled: ____
Distance traveled: ____
Distance traveled: ____
Rf: ________________
Rf: ________________
Rf: ________________
Color:______________
Color:______________
Color:______________
Distance traveled: ____
Distance traveled: ____
Distance traveled: ____
Rf: ________________
Rf: ________________
Rf: ________________
Color:______________
Color:______________
Color:______________
Distance traveled: ____
Distance traveled: ____
Distance traveled: ____
Rf: ________________
Rf: ________________
Rf: ________________
Paste a picture of your chromatograph with a metric ruler that has zero aligned with the pencil
line below.
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Name:
Period:
Teacher:
Date:
Post Lab Questions
1. Which kool-aid coloring is a pure substance? Which kool-aid coloring is a mixture? How do you know?
2. Based on the chart below
identify all the food dyes present in
each flavor of kool-aid
Dyes Present
grape
lemon-lime
orange
red
2. Paper chromatography separates mixtures by their polarities. Water is polar and it dissolves polar things. Knowing
this, which colors from the kool-aid was the most polar (soluble in water)? The least polar? How do you know?
3. Another way of separating a mixture is through distillation. Describe how to separate a mixture of water and
ethanol using distillation. Use table H to help identify the two specific temperatures that will be important to your
separation process.
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Name:
Period:
Teacher:
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4. Base your answers to questions a through c on the particle diagrams below, which show atoms and/or molecules in three different
samples of matter at the same temperature and pressure.
a. Which sample represents a pure substance?
b. When two atoms of y react with one atom of z, a compound
forms. Using the number of atoms shown in sample 2, what is the
maximum number of molecules of this compound that can be
formed?
c. Explain why sample 3 does not represent a compound.
6. Which beaker illustrated below represents homogeneous mixture? Explain
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Name:
Period:
Teacher:
Date:
7. Why do food manufacturers add food dyes to our food if food dyes have no nutritional value?
8. Four watch glasses labeled 1, 2, 3, and 4, each held a few crystals of four different white solid substances. Equal
numbers of drops of a dilute acid were added
to each of the dishes. Nothing else is done to
the containers. The results are listed in the
given table.
Which of these MOST likely reflects a physical
change?
9. The first diagram represents four molecules of a substance before any change has occurred. Which
diagram best represents the same substance after a physical change has occurred?____
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