Paper Chromatography Lab
What are the dye components of marking pen inks?
Chromatography is a physical process in which components of a mixture are separated. The inks of marking pens are often mixtures of several dyes. As the solvent (water) in this lab diffuses through the filter paper, these dyes are dissolved and then carried along by capillary action. Capillary action is the movement of a liquid upward through small pores. Dyes that are more soluble (dissolve better) in water will be moved further. In comparison, the dyes that do not dissolve as well in water, and are attracted to the paper will not be carried as far. Solubility is a physical property, a property of matter that can be observed without chemically changing the substance being studied.
beaker, water, ruler, filter paper, tape, 2 marking pens of different colors.
- Cut two strips of filter paper so that each is 2 cm wide and 9 cm long.
- Tape one end of a strip between the 12 cm and 14 cm marks on the ruler.
- The other strip is taped between 15 cm and 17 cm on the ruler.
- Use a marking pen to draw a single line across the bottom of each filter paper about 2 cm from the bottom of the strips. Use a single, different color pen for each strip.
- Place the ruler with its filter paper strips across the top of the beaker. Note how far into the beaker the paper extends.
- Remove the ruler and paper. Pour enough water into the beaker so that the bottom of the paper will just touch the water surface.
- Place the ruler and paper in the beaker. Make sure the paper doesn't touch the sides of the beaker.
- Observe the dyes move up the filter strip for 10-15 minutes.
- When the water/dye has climbed to within 3 cm of the ruler, lift the ruler out of the beaker and allow the paper to dry slightly.
- Take each strip of paper and display it with the others of that color pen the class has created.
Draw a scale diagram of your two paper chromatography strips showing the starting position of the marker pen line and the subsequent color separations at the end of the experiment. Be sure to completely label the diagrams.
Read and follow the lab report format for conclusions.
Additional questions, answer these in complete sentences.
- Why would the different color dyes separate as capillary action carried the dyes along?
- For the green pen, which color of dye is more soluble? How do you know?
- How is this an example of a separation method based upon matter's physical properties?
- Imagine you are an investigator investigating a forged will. You are trying to determine if a pen from a beneficiaries' home was used to write the forged will. How could you use paper chromatography to help you? Explain in detail.