Solving Mysteries Using Paperchromatography
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Paper chromatography is a way to analyze mixtures, such as ink, by separating them into theoriginal chemicals that are included in their makeup. Crime scene investigators usechromatography to identify and separate many different substances. Detectives often usechromatography to identify drugs from narcotics to aspirin in blood and urine. In thisexperiment, you will use chromatography to solve a make-believe mystery about the identityof a kidnapper.ObjectivesIn this experiment, you will: m Examine and compare ink samples m View and photograph ink samples before and after separation m Learn about ink and why it can be separated into different colorsMaterialsm Power Macintosh G3 or betterm ProScope Digital USB Microscope and softwarem Faded ransom note (see Ģ€Ð*”Teacher informationĢ€ )m Ink samples or watercolor black felt-tip pens (recommended brands: Mr. Sketch, K-Mart,Kodak, Crayola, Wal-Mart, Expresso Fine Tip, Flare Felt Tip, or El Marko by Flare) m Piece of white paperm Piece of white paper towelm An additional white paper towel or a coffee filterm Plastic cup or beakerm Waterm Rubbing alcohol (optional)m Salt or sugar (optional)The ProScope Digital USB Microscope nMiddle School Science Experiment: Solving Mysteries Using Paper Chromatography1
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ProcedureNote to teacher: Place the ransom note on the board and explain that a school staffmember has been kidnapped. Tell the students that the kidnapper left a ransom note in theschoolДўв‚¬Ð²„Ñžs mailbox, but it got wet, became faded, and the ink on the paper became diluted andran. It is no longer readable. (See the Ģ€Ð*”Teacher informationĢ€ section for instructions about thepreparation of the ransom note.) Tell students that FBI agents are on the way, but theprincipal has asked them to help solve the crime. You have narrowed the suspects down to sixor eight (depending on how many pens you have). You have collected the pen each suspectwas using, and now all the students have to do is determine which pen wrote the ransomnote. Put the names of the possible suspects on the board. Put a picture from the ProScopeUSB microscope of the ink both before and after separation on the board next to the actualransom note. You can either prepare samples with all of the pens and hand those out, or handout pens to the students and have them prepare their own samples. Students should thenfollow these instructions:1Fill a plastic cup with water.2If you are using already prepared ink samples, carefully take the ink samples off the piece ofwhite paper. Lay out the writing samples in order so they do not get mixed up. Using theProScope USB microscope, take a picture of each ink sample using the x50 lens.If you are using the different pens to create the ink samples, you should each have a set ofnumbered pens and either a paper towel or a coffee filter. Cut small strips of the paper towelor coffee filter for use in your investigation. The strips should be approximately 1/4 inch by 1-1/2 inches. Put one dot in the middle of each piece of paper with a different pen. Keep thesamples in the correct order. Using the ProScope USB microscope, take a picture of each inksample using the x50 lens. Save the pictures for comparing and contrasting later.3Take the first paper towel and dip the end of it into the cup of water. Do not get the ink markdirectly in the water. Let the paper towel absorb water until it reaches the ink mark. Hold it inthe water for a few more seconds.4Place the wet ink sample on a dry paper towel. Put the samples in numerical order. Make surethey are placed neatly and spaced apart so the ink does not run onto the other samples.Repeat this procedure with all of the ink samples.5Let the wet samples sit on the paper towel for a few minutes until they begin to dry. Next, takea picture of each separated ink sample using the ProScope USB microscope. Compare andcontrast the ink samples with the actual ransom note and the pictures on the board.Determine which pen wrote the ransom note.DataDescribe the process used to identify the kidnapper. Explain how you were able to decidewhich pen wrote the ransom note. Describe how the pictures from the ProScope USBmicroscope helped you form your conclusion. In your report, include your selection of thekidnapper. 2Middle School Science Experiment: Solving Mysteries Using Paper Chromatography nThe ProScope Digital USB Microscope
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Processing the data1. Were the inks used in the pens a compound or a mixture? Explain how you were able todetermine the answer to this question.2. Were the inks in the different pens all the same? Explain how you know the answer.3. Why did the ink move up the paper towel?4. Were you able to distinguish between the ink samples using the ProScope USBmicroscope? Explain how the samples looked through the microscope both before andafter the separation of the ink.Extensionsm Instead of using watercolor markers, use permanent markers and isopropyl (commonrubbing alcohol) as the solvent. The watercolor and permanent markers could both beused, trying water first and then the isopropyl alcohol. You could write your own secretmessages to each other and solve which pen wrote the message. m You can also further experiment by adding salt or sugar to the water and testing the inksamples to see if there is any difference. Does this cause the movement of the ink on thepaper towel to change? Is the method of separating the ink just as effective as the othermethod used?m You can also test other colors in the same brand or in different brands of ink pens. Doesone manufacturer of pens use the same colors in all of their different inks?Teacher informationm To prepare the ransom note, you need a permanent marker and a watercolor marker. (TheMr. Sketch black marker works well for this.) Write the first part of the ransom note with apermanent marker so the ink will not run. Write the second part of the note with the blackMr. Sketch marker. Write the note on a piece of white paper towel. Write something to theeffect of Ģ€Ð*”I have kidnapped (Mr. or Mrs.) _______________. Follow these instructionsor something terrible will happen. No COPS! Put one million dollars in the garbage canbehind the school after midnight. If this is done, (he or she) will be returned safely to youtomorrow.Ģ€ Put the bottom of the paper towel in water so the ink runs up the paper towel.The top half should be readable in the permanent marker, and the bottom half should befaded and the ink should be separated into its original colors. This gives