Chromatography Inquiry: Scientific Performance Task

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Task Author: Judy T. Sweeney
Task Title: Chromatography
Grade Level: 4 Foss Kit Title Inventions Activity # 3
Physical Science Grade 5 Benchmark

Brief Overview of Assignment: Students will use paper chromatography to observe pigments in watercolor inks and invent an application of chromatography.

Targeted Benchmark: The student will identify examples of change over time.

Recommended Prerequisite Student Knowledge and Skills:
Introduce the students to the properties of water including capillary action and the properties of paper including wick. Chromatography, or color writing, is a process using paper and water to separate pigments in ink.
Investigate moving liquids and materials will strong attraction for the paper get left behind first and materials with weak attraction for the paper get carried a long distance. If the material have color, colored bands will be lift on the paper. Water-soluble inks make interesting subjects for chromatography because they use a number of colored materials, capped pigments. Some colors use only one or two pigments. Others such as blacks and browns use many more pigments.

Materials Needed:
Materials Generally Available: basin, rubber bands, paper clips, hand lenses, plastic cup, tape, newspaper, paper towels
Special Items: (Teacher must provide) filter papers, watercolor pens, several black markers

Citation and Helpful Resources: (i.e. books, web sites, etc.)
Kirkpatric, Rena, Rainbow Colors, Raintree, Austin, TX 1991
Anderson, R.L., Light and Color, Raintree, Austin, TX 1978

Recommended Classroom Time: (in hours)
2 Class Periods (30-45 minutes each)
Introduction- Set up investigations with all colors of markers
Students investigate black markers

Detailed Description of Task for Teachers:
After your students have completed Activity 3 in the Foss Kit which includes:
1. Demonstrate marking a paper strip. Use a pen to write a word across the width of the strip 2 cm. from one end.
2. Demonstrate the basin setup. Show the students how to put four rubber bands around the basin so that “clotheslines” are formed over the open basin.
3. Demonstrate handing the paper strip. Show the students how to cover the strip, ink end down, into the basin right next to one of the rubber bands. Explain that when the tip of the paper (not the ink) just touches the water, they should fold the paper over the rubber band so that it will hang at that level. Use a paper clip to secure the rubber band.
4. Prepare basins. After the rubber bands are in place, put about _ liter of water in the basin.
5. Use purple pens to demonstrate. It should take about 3 minutes for the color to move up the paper strip.
6. Discuss what happened.
7. Define pigment and Chromatography. Tell the students that the color in the ink is called pigment. The process by which pigments are made to move using paper and water is chromatography.
8. Introduce the record sheet. Tell the students that they can record the results of several additional chromatography investigation on the sheet. Describe this procedure.
a. Select a colored pen. Make a mark in the color box at the top of one column on the record sheet.
b. Use the same pen to draw two lines on a filter-paper strips 2 cm from each end of the strip.
c. Hang the strip from one of the rubber bands.
d. Remove the completed chromatogram from the rubber band and blot it dry.
e. Make more chromatograms.

Additional Contexts and /or Possible Extensions of Task:
Obtain five different brands of water-soluble felt-tip pens. Label one the mystery pen.

Make a chromatogram from each of the five black pens. Tape the chromatograms to a record sheet or a piece of white paper. Number them 1-5. Cover the paper with clear plastic. Make one sheet for each chromatography station.

Tell the students to look at the chromatograms made by five different pens. Your task is to find out which chromatogram was made from the pen marked “Mystery Pen”

Use the “Mystery Pen” to make a chromatogram. Tape it on a paper. Then answer the questions below.

1. Write the letter of the chromatogram that was made by the “Mystery Pen.”

2. Explain how you know this.

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