CHALK CHROMATOGRAPHY
Introduction
Chromatography is a process which separates the substances in a mixture. The relative sizes of molecules or the charges on ions influence the rates of separation. Gas chromatography separates mixtures of gases and volatile liquids, using metal columns which are thin and very long. Column chromatography uses a liquid medium to separate complex substances such as vitamins, proteins, hormones and DNA. Gel electrophoresis is a form of chromatography used to separate fragments of DNA by their size and electrical charge. Paper or chalk chromatography is used to separate the components of dyes, inks, food coloring and other mixtures by their molecular size and their solubility in polar solvents-- such as water and alcohol.
Student Objectives:
* Students will demonstrate safe laboratory techniques during the lab, including proper use and disposal of methanol.
* Students willanalyze the components of food coloring by separating the colors.
* Students will recognize and identify two or more characteristic properties of the component colors in food coloring.
* Students will design a lab to identify inks or dyes.
* Students will compare his/her data with that of other class members to compile a class data table.
Materials
1. Two beakers 100 ml and 250 ml
2. Food coloring, green, yellow, blue, red
3. White chalk (four pieces)
4. Methanol
5. Small metric ruler
6. Toothpicks
Procedure
1. Stand chalk upright in the 100 ml beaker. If you have trouble, scrape the bottom of the chalk to level it, or, use small piece of clay on the bottom of the chalk.
2. Apply three small dots of one food coloring to the chalk, using the broad end of a toothpick. Place the dots 1.5 cm from the bottom of the chalk, at equal distances around the chalk.
3. Place the chalk back into the beaker and carefully pour 25 ml of methanol into the beaker. (Make sure the chalk is still standing)
4. Quickly invert the 250 ml beaker to cover the first beaker, because methanol is very volatile and will evaporate.
5. Observe the movement of colors in the food coloring as the methanol travels the length of the chalk. Do not let the methanol flow over the top of the chalk! Remove the chalk and allow it to dry, then measure the distance each color traveled. Record all results in the data table.
6. Repeat steps 1-5 with two other food colorings.
7. Complete analysis questions 1 - 4, on page two.
8. Predict the results for red food coloring, then run the procedure.
9. Dispose of the methanol as instructed.
Data
Food Coloring Color on Chalk Color on Chalk Color on Chalk
On Chalk
Distance Distance Distance
Traveled Traveled Traveled
1 (green)
mm mm mm
2 (blue)
mm mm mm
3 (yellow)
mm mm mm
4 (Red)
mm mm mm
Analysis (write on another piece of paper).
1. Using the information in the data table, describe the results for each piece of chalk.
(Include the distances too)
2. What physical characteristics of colors in the food colorings cause them to travel
as they did?
3. Were the colors on each piece of chalk visible in the food coloring before you placed it
on the chalk? Explain your answer.
4. How do the results from each food coloring compare? Do the same colors always move
the same distance? If not, how close are they?
5. Predict the results of repeating this experiment with red food coloring.
Show your prediction to your teacher, then repeat the experiment with red food
coloring. Was your prediction right? Why, or why not?
6. Design a lab to identify inks or dyes using a chromatography process.
7 . List some other practical applications of chromatography.
Conclusion
Write a paragraph explaining the chromatography process and what you learned
by using chromatography.