Radial chromatography Radial paper chromatography and columnar chromatography of the …

Radial Chromatography-Water
Source file content last modified: 4/16/15 3:10:48 PM
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Description

From just a few black dot “seeds” on a piece of filter paper bloom a variety of colorful flower patterns. A demonstration chromatogram on very large filter paper runs concurrently with smaller student chromatograms. Several student problem solving variations are suggested for students familiar with chromatography.


Background

  • Although they appear as one, pure color, most black inks are comprised of a mixture of pigments — sometimes as many as eight or nine. A filter paper wedge acts as a wick, drawing water up to a full circular filter paper spotted with black ink. And as the water is then absorbed outward and flows past the black spots, each of the pigments gets subjected to two opposing forces: its attraction to the filter paper, which is acting to hold the pigment in place and is known as the "stationary phase", and its attraction to the water, which is acting to pull the pigment outward along with it and is known as the "mobile phase". Due to the nature of the molecules that make them up, some of these pigments are more attracted to the filter paper than the water and thus stay more or less where they are spotted, while others are more attracted to the water than the paper and thus move out quite far. Thus, chromatography can be thought of as a race, separating out the fast pigments from the slower ones. The longer the chromatography is allowed to run, the more separated out the pigments become. If, however, the filter paper is not removed before the water reaches the edge, then the pigments, which cannot evaporate the way the water can, are deposited on the edge, one on top of the other. If given long enough, the pigments would eventually end up all together again in a circle along the entire edge of the filter paper. The color of this circle would, of course, be black. To prevent this from happening, then, the filter paper should be lifted up out of the water when the separation is greatest, effectively stopping the race in the middle and freezing the pigments in place.
  • Note that the slower pigments may have a strong attraction to both the water and the filter paper. However, the key is that the slower pigment is attracted to the paper more strongly than to the water; the slower pigment spends more time attached to the paper than dissolved in the moving water.


Chemical Concepts

  1. Although they may appear to be pure substances, many materials are mixtures comprised of two or more different substances.
  2. Substances tend to maintain their unique physical and chemical properties, even when mixed together with other substances.
  3. Due to the nature of their molecules, different substances may have very different affinities for certain materials, such as paper or water.
  4. These differences in affinities may be used in a technique known as chromatography to help separate out and identify the components of various mixtures, such as those used in making commercial inks and dyes.


Safety

No special precautions are required.


Procedure

Make sure your work space has a clean dry surface. Make a careful record of your work in your notebook. Record all relevant information. Use pencil for any labels. The pencil does not run. At the end of the laboratory you use your notebook to compare results with other students and make some decisions.

  1. Obtain a piece of filter paper, and poke a hole (2-3 mm diameter) through its center. Using a pencil, write your initials lightly along the edge of it.
  2. Choose one of the black pens and use it to make five or six dots equally spaced out in a small circle around the center hole. The dots should be about 6-8 mm from the center.
  3. Now select a second pen, a different brand than the first, and use it to make dots in between the first dots. You should end up with 10-12 black dots in a circle about the size of a penny.
  4. Fold a wedge-shaped piece of filter paper length-wise and roll into a cone. Insert it up through the center hole.

    Fill a cup with water to within about a centimeter of the top, and dry the rim with a paper towel. Then, carefully place the filter paper on top of the cup so that the base of the wedge extends down into the water.

    Observe. The process takes 5-10 minutes.
  5. Once the water has spread to within 1-2 cm of the edge, carefully lift up the filter paper and set it on an empty cup to dry.

Large Variation:

Larger flower patterns can be quite impressive, and they can show separation that is not evident on a smaller scale. Students can compare the separation on their small papers with the large separation to see how much more information is present.

In this large variation, evaporation becomes a problem, as does support for the paper as it absorbs. To compensate for evaporation, the chromatography should be conducted in a small, closed container. Some store-bought pie crusts come with aluminum foil pans and matching clear plastic lids; these are ideal for this purpose, as are the hinged plastic pans used for some carry-out foods and in many supermarket bakery departments. A dish pan sealed with plastic wrap or a sheet of plastic works well. Transparent plastic storage (i.e. sweater boxes) cases also work well.

  1. Cut a plastic cup down to the same height as an aluminum pie pan. Cut a wedge of filter paper (from a smaller filter) that is a little taller then the aluminum pie pan. Roll the wedge-shaped piece of filter into a cone to use as a wick.

    Fill the cut-off cup 3/4 full with water and place it in the center of the pan. If you are using an outer container, place the pan in a container.

    Optional:

    Alternately, you may wish to add a plastic tube connected to a funnel to add the water to the cup in the pan. Set up the chromatogram without water. When the demonstration begins, simply add water through the tube. If water runs low, you may add more during the chromatography.
  2. Obtain a large piece of filter paper (24 cm diameter, for example), and poke a hole (3-4 mm diameter) through the center. Spot the paper with black pens in a circle around the center hole. Although a quick, one-time spotting works well for the smaller filter papers, it produces very faint results on the larger ones — since the dyes are being spread over a greater area. It is recommended, therefore, that the larger filter paper be spotted with proportionately more ink, either by holding the pen in place (which tends to create larger dots) or by going over and over the same spots several times.
  3. Insert the wick in the filter paper and lay it on top of the pan so that the wick extends into the cup. The rim of the cup supports the center of the filter paper; the rim of the pan supports the outer edge.

  4. Carefully cover the system. Either place the plastic lid mouth-downward on top of the set-up or cover the outer container with plastic. If you set up the tubing option, add water when you want to start.
  5. Observe. Allow the chromatogram to run until the water has spread to within 1-2 cm of the outer edge, which may take anywhere from 50-100 minutes. (The chromatogram in the movie ran 80 minutes.)

Questions

  1. Which pigment in your pen is most attracted to the mobile phase (water) relative to the stationary phase (paper)?
  2. Which pigment in your pen is most attracted to the stationary phase (paper) relative to the mobile phase (water)?


Handout Makeup

Name ___________________________ Class _______

Teacher __________________________



BeckerDemos 037 Radial Chromatography-Water

Watch the movies.

  1. Describe the separations.
  2. Use the movies to answer the questions.


Curriculum-

  • At the elementary level — after discussing colors and color mixing, use this activity to show the opposite: color separating.
  • At the secondary level — incorporate with other separation techniques, ties in well with polar/nonpolar and intermolecular forces. Use when discussing solutions and solubility.


Activity-

  • Laboratory or Home Experiment
  • This activity is best done as a hands on lab, not as a demonstration. Students can work individually or in pairs and will probably want to keep the final product. The activity also makes an ideal at-home project, for it is safe and requires no special equipment.
  • You may wish to do the Large Variation as a demonstration while students work on small ones. You may wish to set up a fresh one for each class but stop the chromatograms at different points. Display all of the chromatograms the next day. The large chromatogram displays separations not present in the student chromatograms.
  • Note the variations in Lab Hints. These variations present problem solving aspects to the activity for students who have done chromatography before.


Safety-

No special precautions are required.


Time-

Teacher Preparation: 1-2 minutes

Class Time: 15-20 minutes


Materials-


Student Experiment per student

  • 1 nail
  • 1 pair of scissors
  • filter papers (9-13.0 cm diameter) 3-4 for each student. (Coffee filters can be used but give much less impressive results.)
  • 4-5 pencils
  • a collection of water soluble black pens, felt tip and/or roller point, as many different brands as possible
  • plastic cups, 2 for each student
  • paper towels
  • water


Large Demonstration

  • 1 plastic cup
  • 1 filter paper (20-30 cm diameter)
  • 1 filter paper (9-13.0 cm diameter) for wick
    • 1 aluminum pie tin with plastic cover
      • or
    • 1 dish pan and plastic to hold and cover the pie tin (optional plastic tubing)


Disposal-

No special precautions are required.


Lab Hints-

  1. Cut 2 or 3 filter papers up into wedge-shaped pieces — triangles 3-4 cm tall and 1-2 cm at their base. The wedges can also be made out of absorbent paper towels.
  2. To save time, make the holes in the filter paper before class. Use the nail to poke a small hole (2-3 mm in diameter) in the center of each of the remaining filter papers. These may be done three or four at a time. If a drill is available, use a 1/8" bit on whole stack of filter papers. 100 sheets can be done in just a few seconds!


Variation A:

The following activity serves as a good way to introduce the whole concept of chromatography and its value as an analytical tool.

Before class, prepare several filter papers by making 4-5 dots with one black pen and 1 dot with a different black pen. The dots should all be as similar to one another as possible and all evenly spaced out, so that there is virtually no way of telling which dot is the different one. (or perhaps the easier way is to have them all a little different, but with still no indication of which dot was made with a different pen). Hand them out to the students, individually or in pairs, and have them predict which dot was made with a different black ink than the others. They should circle their predictions lightly with a pencil. Then have the students insert the wicks and place them in water. As the chromatograms run, they see that although the dots all looked the same in the beginning, one of them separates out very differently than the others. Because they circled their predictions, they each have a vested interest in the outcome of their chromatogram! This activity is a good lead in for discussions on separation and identification techniques and for the other radial chromatography activities.


Variation B:

  1. Find 6-8 black pens that each produce a unique spread of colors. Then purchase a second set of the exact same pens. Label one set of pens with numbers: "1"-"8" for instance, and label the other set with letters (in scrambled order): "A"-"H" for instance. Try also to cover up any brand names that may be visible.
  2. Divide the class into two equal-sized groups and have them working at opposite ends of the room, one with one set of pens, the other with the other set. As they spot their filter papers, have them write down in their notebooks or on their lab sheets the numbers (or letters) of the two pens they used. While the water is spreading, collect all the pens.
  3. After the colors have been separated out, have the two groups come together to compare their results, and to see if they can collectively figure out what number corresponds to what letter for the two sets of pens. Because each student has two patterns, and because it is unlikely that they remember which pen they spotted where, this can prove more challenging than it sounds! When they think they have the correct match-ups, you may bring out the pens and let them see for themselves whether they were right or not.


Variation C:

  1. For a more open-ended and more challenging variation, try the following. Find two pens that produce unique and attractive color spreads, and purchase twelve to fifteen of each. Place one of each type in a plastic bag along with 8-10 filter papers and 8-10 wedges. Before hand, follow the procedure steps outlined above to make a flower pattern to serve as a model. Then, at the beginning of class, show the students the model and challenge them to reproduce it as best as they can. Have them work in groups of two or three; hand each group their bag of supplies along with a cup, and warn them to think first, for they are only allowed as many tries as they have filter papers!
  2. If they are not familiar with the process of chromatography, they might insist that they need more pens, that they cannot possibly produce all the different colors using just black ink. If they have already done the traditional chromatography — where the dyes are spread out parallel to one another along on a vertical rectangle of filter paper — then they certainly have a head start. They still need to figure out, however, a procedure to get the colors to spread out in a radial fashion.


Observations-

  • A closer look at the chromatography pattern would indicate that there is a lot more going on than just pigments traveling at different "speeds." Some of the pigments end up in very concentrated zones; others are more diffuse. Some pigments tend to streak out in lines; others tend to form fan-like patterns. Some pigments appear to "avoid" other pigments, edging around them instead of passing through. These effects are most likely a result of the intermolecular forces within the pigments and between one pigment and another.
  • The diffuse bands are a rate of reaction problem. If the equilibrium of the pigment distribution between the stationary and mobile phase is established slowly, then diffuse bands are observed. Paper is cellulose with many OH sites for hydrogen bonding interactions similar to those in water. Where strong interactions (higher activation energies) occur, reactions are frequently slow enough to smear the band. Chromatography bands sharpen at higher temperatures.


Answers-

Q1. Which pigment in your pen is most attracted to the mobile phase (water) relative to the stationary phase (paper)?

A1. Answers vary with brand name of the pens. It is the color that travels the furthest. (In the movie, navy blue spends the most time in the water phase of any of the dyes.)
Q2. Which pigment in your pen is most attracted to the stationary phase (paper) relative to the mobile phase (water)?

A2. Again, answers will vary with brand name of the pens. It is the one that travels the least. (In the movie, a yellow dye in one pen and a second purple band from the other pen move most slowly.)


Key Words 1-

solutions, solubility, chromatography, adsorption, separation


This static was created at 3:10:48 PM on Thursday, April 16, 2015

Radial Chromatography-Water
Source file content last modified: 4/16/15 3:10:48 PM
Display Content Selector
See Previous: Ionic Crescendo
See Next: Radial Chromatography T-Shirt Designs

Description

From just a few black dot “seeds” on a piece of filter paper bloom a variety of colorful flower patterns. A demonstration chromatogram on very large filter paper runs concurrently with smaller student chromatograms. Several student problem solving variations are suggested for students familiar with chromatography.


Background

  • Although they appear as one, pure color, most black inks are comprised of a mixture of pigments — sometimes as many as eight or nine. A filter paper wedge acts as a wick, drawing water up to a full circular filter paper spotted with black ink. And as the water is then absorbed outward and flows past the black spots, each of the pigments gets subjected to two opposing forces: its attraction to the filter paper, which is acting to hold the pigment in place and is known as the "stationary phase", and its attraction to the water, which is acting to pull the pigment outward along with it and is known as the "mobile phase". Due to the nature of the molecules that make them up, some of these pigments are more attracted to the filter paper than the water and thus stay more or less where they are spotted, while others are more attracted to the water than the paper and thus move out quite far. Thus, chromatography can be thought of as a race, separating out the fast pigments from the slower ones. The longer the chromatography is allowed to run, the more separated out the pigments become. If, however, the filter paper is not removed before the water reaches the edge, then the pigments, which cannot evaporate the way the water can, are deposited on the edge, one on top of the other. If given long enough, the pigments would eventually end up all together again in a circle along the entire edge of the filter paper. The color of this circle would, of course, be black. To prevent this from happening, then, the filter paper should be lifted up out of the water when the separation is greatest, effectively stopping the race in the middle and freezing the pigments in place.
  • Note that the slower pigments may have a strong attraction to both the water and the filter paper. However, the key is that the slower pigment is attracted to the paper more strongly than to the water; the slower pigment spends more time attached to the paper than dissolved in the moving water.


Chemical Concepts

  1. Although they may appear to be pure substances, many materials are mixtures comprised of two or more different substances.
  2. Substances tend to maintain their unique physical and chemical properties, even when mixed together with other substances.
  3. Due to the nature of their molecules, different substances may have very different affinities for certain materials, such as paper or water.
  4. These differences in affinities may be used in a technique known as chromatography to help separate out and identify the components of various mixtures, such as those used in making commercial inks and dyes.


Safety

No special precautions are required.


Procedure

Make sure your work space has a clean dry surface. Make a careful record of your work in your notebook. Record all relevant information. Use pencil for any labels. The pencil does not run. At the end of the laboratory you use your notebook to compare results with other students and make some decisions.

  1. Obtain a piece of filter paper, and poke a hole (2-3 mm diameter) through its center. Using a pencil, write your initials lightly along the edge of it.
  2. Choose one of the black pens and use it to make five or six dots equally spaced out in a small circle around the center hole. The dots should be about 6-8 mm from the center.
  3. Now select a second pen, a different brand than the first, and use it to make dots in between the first dots. You should end up with 10-12 black dots in a circle about the size of a penny.
  4. Fold a wedge-shaped piece of filter paper length-wise and roll into a cone. Insert it up through the center hole.

    Fill a cup with water to within about a centimeter of the top, and dry the rim with a paper towel. Then, carefully place the filter paper on top of the cup so that the base of the wedge extends down into the water.

    Observe. The process takes 5-10 minutes.
  5. Once the water has spread to within 1-2 cm of the edge, carefully lift up the filter paper and set it on an empty cup to dry.

Large Variation:

Larger flower patterns can be quite impressive, and they can show separation that is not evident on a smaller scale. Students can compare the separation on their small papers with the large separation to see how much more information is present.

In this large variation, evaporation becomes a problem, as does support for the paper as it absorbs. To compensate for evaporation, the chromatography should be conducted in a small, closed container. Some store-bought pie crusts come with aluminum foil pans and matching clear plastic lids; these are ideal for this purpose, as are the hinged plastic pans used for some carry-out foods and in many supermarket bakery departments. A dish pan sealed with plastic wrap or a sheet of plastic works well. Transparent plastic storage (i.e. sweater boxes) cases also work well.

  1. Cut a plastic cup down to the same height as an aluminum pie pan. Cut a wedge of filter paper (from a smaller filter) that is a little taller then the aluminum pie pan. Roll the wedge-shaped piece of filter into a cone to use as a wick.

    Fill the cut-off cup 3/4 full with water and place it in the center of the pan. If you are using an outer container, place the pan in a container.

    Optional:

    Alternately, you may wish to add a plastic tube connected to a funnel to add the water to the cup in the pan. Set up the chromatogram without water. When the demonstration begins, simply add water through the tube. If water runs low, you may add more during the chromatography.
  2. Obtain a large piece of filter paper (24 cm diameter, for example), and poke a hole (3-4 mm diameter) through the center. Spot the paper with black pens in a circle around the center hole. Although a quick, one-time spotting works well for the smaller filter papers, it produces very faint results on the larger ones — since the dyes are being spread over a greater area. It is recommended, therefore, that the larger filter paper be spotted with proportionately more ink, either by holding the pen in place (which tends to create larger dots) or by going over and over the same spots several times.
  3. Insert the wick in the filter paper and lay it on top of the pan so that the wick extends into the cup. The rim of the cup supports the center of the filter paper; the rim of the pan supports the outer edge.

  4. Carefully cover the system. Either place the plastic lid mouth-downward on top of the set-up or cover the outer container with plastic. If you set up the tubing option, add water when you want to start.
  5. Observe. Allow the chromatogram to run until the water has spread to within 1-2 cm of the outer edge, which may take anywhere from 50-100 minutes. (The chromatogram in the movie ran 80 minutes.)

Questions

  1. Which pigment in your pen is most attracted to the mobile phase (water) relative to the stationary phase (paper)?
  2. Which pigment in your pen is most attracted to the stationary phase (paper) relative to the mobile phase (water)?


Handout Makeup

Name ___________________________ Class _______

Teacher __________________________



BeckerDemos 037 Radial Chromatography-Water

Watch the movies.

  1. Describe the separations.
  2. Use the movies to answer the questions.


Curriculum-

  • At the elementary level — after discussing colors and color mixing, use this activity to show the opposite: color separating.
  • At the secondary level — incorporate with other separation techniques, ties in well with polar/nonpolar and intermolecular forces. Use when discussing solutions and solubility.


Activity-

  • Laboratory or Home Experiment
  • This activity is best done as a hands on lab, not as a demonstration. Students can work individually or in pairs and will probably want to keep the final product. The activity also makes an ideal at-home project, for it is safe and requires no special equipment.
  • You may wish to do the Large Variation as a demonstration while students work on small ones. You may wish to set up a fresh one for each class but stop the chromatograms at different points. Display all of the chromatograms the next day. The large chromatogram displays separations not present in the student chromatograms.
  • Note the variations in Lab Hints. These variations present problem solving aspects to the activity for students who have done chromatography before.


Safety-

No special precautions are required.


Time-

Teacher Preparation: 1-2 minutes

Class Time: 15-20 minutes


Materials-


Student Experiment per student

  • 1 nail
  • 1 pair of scissors
  • filter papers (9-13.0 cm diameter) 3-4 for each student. (Coffee filters can be used but give much less impressive results.)
  • 4-5 pencils
  • a collection of water soluble black pens, felt tip and/or roller point, as many different brands as possible
  • plastic cups, 2 for each student
  • paper towels
  • water


Large Demonstration

  • 1 plastic cup
  • 1 filter paper (20-30 cm diameter)
  • 1 filter paper (9-13.0 cm diameter) for wick
    • 1 aluminum pie tin with plastic cover
      • or
    • 1 dish pan and plastic to hold and cover the pie tin (optional plastic tubing)


Disposal-

No special precautions are required.


Lab Hints-

  1. Cut 2 or 3 filter papers up into wedge-shaped pieces — triangles 3-4 cm tall and 1-2 cm at their base. The wedges can also be made out of absorbent paper towels.
  2. To save time, make the holes in the filter paper before class. Use the nail to poke a small hole (2-3 mm in diameter) in the center of each of the remaining filter papers. These may be done three or four at a time. If a drill is available, use a 1/8" bit on whole stack of filter papers. 100 sheets can be done in just a few seconds!


Variation A:

The following activity serves as a good way to introduce the whole concept of chromatography and its value as an analytical tool.

Before class, prepare several filter papers by making 4-5 dots with one black pen and 1 dot with a different black pen. The dots should all be as similar to one another as possible and all evenly spaced out, so that there is virtually no way of telling which dot is the different one. (or perhaps the easier way is to have them all a little different, but with still no indication of which dot was made with a different pen). Hand them out to the students, individually or in pairs, and have them predict which dot was made with a different black ink than the others. They should circle their predictions lightly with a pencil. Then have the students insert the wicks and place them in water. As the chromatograms run, they see that although the dots all looked the same in the beginning, one of them separates out very differently than the others. Because they circled their predictions, they each have a vested interest in the outcome of their chromatogram! This activity is a good lead in for discussions on separation and identification techniques and for the other radial chromatography activities.


Variation B:

  1. Find 6-8 black pens that each produce a unique spread of colors. Then purchase a second set of the exact same pens. Label one set of pens with numbers: "1"-"8" for instance, and label the other set with letters (in scrambled order): "A"-"H" for instance. Try also to cover up any brand names that may be visible.
  2. Divide the class into two equal-sized groups and have them working at opposite ends of the room, one with one set of pens, the other with the other set. As they spot their filter papers, have them write down in their notebooks or on their lab sheets the numbers (or letters) of the two pens they used. While the water is spreading, collect all the pens.
  3. After the colors have been separated out, have the two groups come together to compare their results, and to see if they can collectively figure out what number corresponds to what letter for the two sets of pens. Because each student has two patterns, and because it is unlikely that they remember which pen they spotted where, this can prove more challenging than it sounds! When they think they have the correct match-ups, you may bring out the pens and let them see for themselves whether they were right or not.


Variation C:

  1. For a more open-ended and more challenging variation, try the following. Find two pens that produce unique and attractive color spreads, and purchase twelve to fifteen of each. Place one of each type in a plastic bag along with 8-10 filter papers and 8-10 wedges. Before hand, follow the procedure steps outlined above to make a flower pattern to serve as a model. Then, at the beginning of class, show the students the model and challenge them to reproduce it as best as they can. Have them work in groups of two or three; hand each group their bag of supplies along with a cup, and warn them to think first, for they are only allowed as many tries as they have filter papers!
  2. If they are not familiar with the process of chromatography, they might insist that they need more pens, that they cannot possibly produce all the different colors using just black ink. If they have already done the traditional chromatography — where the dyes are spread out parallel to one another along on a vertical rectangle of filter paper — then they certainly have a head start. They still need to figure out, however, a procedure to get the colors to spread out in a radial fashion.


Observations-

  • A closer look at the chromatography pattern would indicate that there is a lot more going on than just pigments traveling at different "speeds." Some of the pigments end up in very concentrated zones; others are more diffuse. Some pigments tend to streak out in lines; others tend to form fan-like patterns. Some pigments appear to "avoid" other pigments, edging around them instead of passing through. These effects are most likely a result of the intermolecular forces within the pigments and between one pigment and another.
  • The diffuse bands are a rate of reaction problem. If the equilibrium of the pigment distribution between the stationary and mobile phase is established slowly, then diffuse bands are observed. Paper is cellulose with many OH sites for hydrogen bonding interactions similar to those in water. Where strong interactions (higher activation energies) occur, reactions are frequently slow enough to smear the band. Chromatography bands sharpen at higher temperatures.


Answers-

Q1. Which pigment in your pen is most attracted to the mobile phase (water) relative to the stationary phase (paper)?

A1. Answers vary with brand name of the pens. It is the color that travels the furthest. (In the movie, navy blue spends the most time in the water phase of any of the dyes.)
Q2. Which pigment in your pen is most attracted to the stationary phase (paper) relative to the mobile phase (water)?

A2. Again, answers will vary with brand name of the pens. It is the one that travels the least. (In the movie, a yellow dye in one pen and a second purple band from the other pen move most slowly.)


Key Words 1-

solutions, solubility, chromatography, adsorption, separation


This static was created at 3:10:48 PM on Thursday, April 16, 2015