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Paper Chromatography Science Fair Project Idea to Separate Food Colors
What is Chromatography? Definition and Chemistry
Chroma means color. The first person who used this technique used it to separate substances that were colored. So he called it CHROMAtography. Chromatography is a group of methods that are used to separate a mixture of chemicals by the difference in how fast they move. When substances have different chemical properties(for example, charge) or physical properties (for example size) and have colors, these substances can be separated by chromatography and their colors help us to identify the substance.Paper Chromatography
What does the paper do in paper chromatography?
Paper has two characteristics.
- Paper is porous. A filter paper is very porous. (Paper is made up of intertwined fibers that leave a lot of holes (pores) that are well connected. These pores are so small that we cannot see them with our eyes. However small particles may be able to pass through these pores depending on how large the pore is and how small the particles are.) The continuously connected pores act like a capillary and water can go up these pores by a process called "capillary action". Capillary action is the movement of water within the spaces of a porous material.
- Paper has affinity ('likes') to water.
When you spill your soda on the dining table you quickly grab a paper towel and wipe it out. Now look at the paper towel!! All that soda is absorbed on to it!!! This is because water goes into the paper towel by CAPILLARY ACTION and water stays there sticking to the paper towel as it has affinity to the paper.
What if you take a strip of filter paper(coffee filter) and dip one end into water and hold the paper vertical. You will see water climbing up the paper. Why? The same reason, capillary action and water 'likes' paper. The smallest water particle is called a water molecule. As water molecule #1 starts climbing on to the paper, it pulls along water molecule #2, which of course, is dragging water molecule #3, and so on.
The secret of paper chromatography separation
The secret of separation of substances by paper chromatography is that there is no secret.If you have a substance that is colored red and is soluble in water, put a drop of this red color substance near the edge of a paper and let water climb up the paper and pass through the red spot. You will see the red color moving with the water. If you keep it for a while you might see the color lagging behind the water front! Wow! we got it, right?
Why should the color lag behind the water front? You know it is not just the color that is moving, it is the substance that has the color that is moving. The molecules of this substance may be attracted to the paper more strongly than water molecules are attracted to the paper. You got the reason number one. The molecules of this substance may be bigger than water and hence heavy. So it cannot move as fast as water. Now you got the reason number 2.
Suppose you have two substances that are made of equally heavy molecules, but one of them attract paper very strongly and the other attracts less strongly. Make a mixture of these two substances and spot near the edge of a strip of filter paper as above. Dip the edge in water and "run" a chromatogram. What will happen? Both the substances move at different speeds and after some time they will separate from each other.
Wow! You separated two substances from a mixture of these substances using a paper chromatography. This is exactly what it is used for!! Wait a minute, how will you say they are separated? You can tell that they are separated by looking at the chromatogram, only if these substances are colored. So we can do an ink chromatography or a food color chromatography to separate colored individual substances in the ink or food color. Now let's do an experiment. (This is an ideal experiment for elementary school children in grades 3-5). The following is the step-by-step description of a science fair project done by an elementary school student. To cite this page, the link is http://www.sciguru.com/science-projects/ or SciGuru.com Science Projects
The Big Experiment
Aim: To separate two colored substances using paper chromatographyMaterials:
A filter paper strip
Red and Blue food colors
A dropper with pointed tip
A small container or tube to hold colors
A stand to hold the paper
Clips or tapes to hold the paper on the stand.
A tray or shallow container to place water
One cup of water
Method: Cut a filter paper of 1 inch width and 8 inches length. Fill the tray with water. Mix red and blue food colors in equal quantities in the small dish. Using a dropper place a small drop of mixed colors near one of the edges of filter paper. Hang the paper on the stand and allow it to dry for few minutes. Place the hanging paper strip above the water such that the spotted edge is touching the water in the tray. Make sure the color spot is above the water level. Wait until the water climbs upto about 7 inches. Remove the filter paper from the stand and allow it to dry. Check the colors.
Result: When red and blue colors were mixed, a purple color was obtained. When the purple color solution was spotted on the paper and "chromatographed" they separated into red and blue.
Conclusion: Paper chromatography can be used to separate some colored substances from their mixture.
To cite this page, the link is http://www.sciguru.com/science-projects/ or SciGuru.com Science Projects