TO THE STUDENT

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 12 marked chromatography strips, hole punched 3 unmarked chromatography strips, hole punched 5 250-ml containers 5 drinking straws 1 black marker paper towels straightedge tap water tape metric ruler pen or pencil

Paper Chromatography

Paper chromatography is a technique that can be used to separate certain chemicals from each other. In this event, you will use paper chromatography to separate the inks which have been placed on several strips of chromatography paper. You will also use paper chromatography to identify the ink in a marking pen.

1. Find the fifteen paper strips in your materials (three each labeled A, B, C, D, and three unlabeled). When handling the strips, pick up the strips by a corner nearest the punched hole. Strips A, B, C, and D are already marked with a black pen line. Use the black pen provided and a straightedge to draw black lines on the unmarked strips at the ends furthest from the punched hole. Draw straight lines 2 cm from the end of each unmarked strip.

2. Add tap water to a depth of 1 cm in each of the five plastic cups.

3. Each member of the group should take three strips (for example, A, A, A) and place a drinking straw through the punched holes in the tips of the strips. Suspend the strips in the cup so the tips are under water. Do not allow the black pen lines on the strips to be under water. Do not allow the strips to contact each other. See the diagram below.
   

4. Allow the experiment to run until the water approaches the bottom of the punched holes. Remove the strips from the cups. Take the strips off the straws and lay the strips out on a paper towel.

5. Cut each strip in two lengthwise so that each member of the group has one of each. Make sure that each piece is correctly labeled. The pieces of the strips originally unmarked should now be marked E. Tape the strips in your test booklet. If there are extra strips, discard them.

When your strips are dry, tape each of the strips in the space below.

Strip A

Strip B

Strip C

Strip D

Strip E

Questions

Please answer the following questions by yourself.

1. Were the black pen lines on Strips A, B, C, D, and E made by the same pens? Using your results, explain why you think the lines were or were not made by the same pens.

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2. Suppose that one paper strip was marked with two of the links used in this experiment, and the two ink lines on the strip were drawn on top of each other. Design and discuss an experiment that could be used to identify these two inks.

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