Paper ChromatographySeparation of a mixture by taking advantage of the differing attractive forces of the substances within a mixture with those of a transport medium and a solvent. Stationary Phase – (the paper) does not move. Holds the sample. Mobile Phase – (the water) a solvent that rises up the paper (stationary phase) and reacts with the sample.Components of the mixture react with both phases. The higher a components polarity the faster it will react with and move with the water(mobile phase). Less polar components will react better with the stationary phase (the paper) and travel slower.
How does this work?• Because molecules in ink and other mixtures have different characteristics (such as size and solubility), they travel at different speeds when pulled along a piece of paper by a solvent (in this case, water). For example, black ink contains several colors. When the water flows through the black ink, the molecules of each one of the colors behave differently, resulting in a sort of “rainbow” effect. Many common inks are water soluble and spread apart into the component dyes using water as a solvent. If the ink you are testing does not spread out using water, it may be “permanent” ink. In such cases, you will have to use a different solvent such as rubbing alcohol.
Whodunnit?A picture of this cuddly teddy bear was sent tohis family along with a ransom not that read; “I hav the bare. If you’s ever wants to see him again you’s better gives me what I asks for. If you’s what call the cops thing will go very bad.”
The culpritsKermit the Frog Big Bird Cookie Monster Bert (NLN) Caught with Caught with Caught with Caught with Pen A Pen B Pen C Pen D
Standard ChromatographChromatograph of ink sampletaken from ransom note.
Materials• Assorted black Pens• 1000 mL Beaker• Chromatography Paper• Pencil• Ruler• Water
Procedure1. Acquire a strip of chromatography paper.2. Fold the top of the strip and staple it to create a loop.3. Draw a line in pencil across the bottom of the strip about 3 cm from the edge and attach a paper clip to the bottom of the paper.4. Place a dot of ink from each of the four sample pens (A, B, C, D) across the line. Label the dots in pencil to identify the pen they came from.5. Poke a pencil through the loop you just made. Use the pencil to suspend the strip in a small glass or container.6. Carefully add water to the glass until it reaches the bottom of the paper strip just below the ink dot. Be sure the ink stays above the water and the paper stays in the water.7. Allow the water to soak up the strip (20 mins) and watch what happens to the ink drop. Record these changes as observations in your lab report8. After about 20 minutes remove the strip from the water and mark in pencil where the water line has stopped. This indicates the distance traveled by the solvent.9. Compare the results of your chromatography paper to the standard chromatograph of the sample of ink taken from the ransom note to determine which pen was used to write the note.
Conclusion• From the results of your chromatography experiment determine which pen’s ink matches the ink sample from the note• Read pages 662-664 in the text book.• Answer questions 1, 2, 3, 4, 5