Setting up ink chromatography is a straightforward and engaging way to reveal the hidden colors within a single ink, demonstrating the fascinating principles of separation science. This simple experiment allows you to visually separate the different colored pigments that combine to make a specific ink.
What is Ink Chromatography?
Ink chromatography is a technique used to separate mixtures. In this context, it separates the different colored components of ink. It works on the principle that different substances travel at different speeds through a stationary phase (like filter paper) when carried by a mobile phase (the solvent). The separation occurs because components of the ink have varying solubilities in the solvent and different affinities for the filter paper, causing them to move at different rates and thus separate.
Essential Materials for Ink Chromatography
To perform ink chromatography, you'll need a few common household items and laboratory basics.
- Filter paper: Coffee filters, paper towels, or specialized chromatography paper can be used.
- Ink samples: Various pens (water-based markers, non-permanent markers) work best.
- Solvent: Either water or rubbing alcohol (isopropyl alcohol) will serve as the solvent, depending on the ink type.
- Tall, clear container: A glass jar, beaker, or a tall drinking glass.
- Pencil: For drawing a baseline on the filter paper.
- Ruler: To measure accurately.
- Scissors: To cut the filter paper to size.
- Tape or paper clip: To suspend the filter paper.
Common Solvents for Ink Chromatography
| Solvent Type | Common Uses | Notes |
|---|---|---|
| Water | Most washable markers, food dyes | Good for water-soluble inks. |
| Rubbing Alcohol | Permanent markers, ballpoint pen inks | Effective for inks that are not water-soluble. (Our case example) |
Step-by-Step Setup Guide
Follow these steps to set up your ink chromatography experiment:
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Prepare Your Filter Paper:
- Cut a strip of filter paper (or a coffee filter) long enough to nearly reach the bottom of your container and wide enough to fit without touching the sides.
- Using a pencil (not ink, as it will also separate!), draw a straight line horizontally across the paper about 1-2 cm (0.5-1 inch) from one end. This is your "baseline."
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Apply the Ink Sample:
- A small sample of the ink to be investigated is placed on the bottom of the filter paper along the pencil baseline. For best results, apply a concentrated, small spot or a thin line of ink directly onto the pencil line. Avoid making the spot too large or too thick, as this can hinder clear separation. Let it dry for a moment.
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Select and Prepare the Solvent:
- Choose your solvent (water or rubbing alcohol) based on the ink you are testing.
- Pour a small amount of the chosen solvent into the bottom of your clear container. The depth of the solvent should be just enough so that when the filter paper is suspended, the ink spot on the baseline remains above the solvent level. It's crucial that the ink spot does not touch the solvent directly at the beginning.
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Set Up the Experiment:
- Carefully suspend the filter paper in the container. You can do this by taping the top end of the paper to a pencil or ruler placed across the rim of the container, or by using a paper clip to hang it.
- Ensure the bottom edge of the filter paper (below the ink spot) is immersed in the solvent, but the ink spot itself is clearly above the solvent line. Ensure the paper hangs straight without touching the sides of the container.
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Initiate Separation:
- Once the paper is in place, the solvent is allowed to be drawn through the filter paper via capillary action. This means the solvent will slowly begin to move upwards through the paper, against gravity.
- As the solvent moves up, it dissolves the ink and carries its constituent pigments along with it. Different pigments will travel at different speeds, separating from each other and forming distinct bands of color up the paper.
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Observe and Analyze:
- Allow the solvent to travel nearly to the top of the filter paper. This may take anywhere from a few minutes to an hour, depending on the solvent and paper type.
- Once the solvent front is close to the top, carefully remove the filter paper from the container.
- Immediately draw a pencil line at the highest point the solvent reached (the solvent front).
- Let the paper dry completely. You will now be able to see the separated colors from your original ink!
Key Principles in Action
During the process, two main factors influence how far each pigment travels:
- Solubility: Pigments that are more soluble in the solvent will travel further up the paper.
- Adsorption: Pigments that have a stronger attraction to the filter paper (adsorb more readily) will travel less distance.
The interplay of these forces causes the different components of the ink to separate into distinct bands, creating a colorful chromatogram.
Tips for Best Results
- Use Fresh Solvent: Always use fresh solvent for each experiment to prevent contamination and ensure clear separation.
- Don't Overload Ink: A small, concentrated ink spot works better than a large, diffuse one.
- Keep Stable: Ensure your setup is stable and undisturbed while the solvent is running to prevent uneven solvent flow.
- Experiment with Different Inks: Try various brands and types of pens (e.g., black, blue, green markers, ballpoint pens) to see a wide range of separations.
By following these steps, you can easily set up and observe the fascinating process of ink chromatography, revealing the colorful science hidden in everyday inks.
