Contributed by: Council of Chief State School Officers (CCSSO)
TO THE STUDENT
Welcome to this experimental science exercise. We hope that you will
find it interesting and worthwhile. Carefully read through these directions
and the directions on the next page before you begin to work.
You may be part of a group for the first part of this exercise.
Each group should carry out the experiment and collect the data
together, but each student must record the data in his or her own
booklet. Be sure to record the data exactly as you observe them.
After the data has been collected, each student should answer the
questions independently.
After you have finished your experiment and have recorded all
of the data, you will be asked to answer some questions about the
experiment and the data you recorded. Your answers must be written
in this test booklet in the space provided. Make sure that you understand
each question before you begin to write. At any time while you are
writing your answers, you may look back to the directions for the
experiment and the data you collected. Be sure that your answers
are written as clearly and neatly as possible.
Before you turn the page, read the list of materials given below
and check to make sure that your group has everything listed.
Materials
- cup
- filter paper
- tap water
- paper towels
- rulers
- candy
- pen or pencil
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AFTER YOU HAVE READ THE DIRECTIONS, TURN TO THE NEXT PAGE AND BEGIN.
Paper Chromatography
In developing a food product, you would want to consider the chemical
content of its ingredients. For instance, since consumers with certain
allergies may need to know about the dyes used in food, you should
be able to identify the dyes in your product.
Paper chromatography is a process that can be used to separate
the components of a mixture. The advantage of this process is that
relatively small quantities of substances, including food components,
can be detected in a simple and fast manner. Mixtures or solutions
of metals, dyes, blood, urine, or antibiotics, for example, can
easily be separated by the various chromatographic methods available
to chemists today.
In this activity you will apply the analytical technique of paper
chromatography to examine the dyes found in the colored shells of
candy.
Read all of the instructions before proceeding. You will be working
with a partner while performing the experiment and collecting the
data. Both partners are responsible for recording the data. You
will be working alone while responding to the questions. Your teacher
will tell you where all the materials you need are located.
- Be careful to handle the filter paper only by the edge.
- Draw a horizontal line in pencil approximately 1.0 cm
from the short end of each strip of filter paper. Lightly draw
a dashed line approximately 2.0 cm from the opposite end.
- Add tap water to the cup to a depth of about 0.75 cm. The water
level in the cup must be below the level of the first line you
drew.
- Moisten a green, yellow, or brown candy. Now rub the candy's
coating on the filter paper. Your goal is to transfer colored
coating onto the paper. Transfer colored coating onto the paper
in the area just above the first pencil line you drew.
- Repeat this procedure so that you have green, yellow, and brown
candy coatings on three different strips of filter paper.
- Make sure that the chromatography paper has thoroughly dried
before proceeding further and that you have labeled each strip
with a G, Y, or B to help you remember what color coating is on
each strip. The labeling should be done at the top of the strip
above the dashed line.
- Carefully lower each strip into the water in the cup. Do
not lower any of the strips beyond the 1 cm pencil line you marked
previously. Hold each strip in place until the water has risen
on the strips to the dashed line, or for 5 minutes (whichever
comes first). Tip: It may be more convenient for you to
do one strip at a time.
- Do not throw your chromatography strips away. You will need
to analyze the results in Question 1.
- After you have finished, be sure to clean up your work area.
Questions
Please answer the following questions by yourself.
- Describe the components of each dye used in the candy coatings
based upon the chromatography you have just performed.
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- Organic chemists, as well as other scientists, often use this
technique to determine if a chemical reaction has occurred or
to separate the components of a mixture. Explain, using an example,
how and why the result from this type of analysis are useful.
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