Rainbow Separation

Introduction:

In the real world, it is often difficult to tell whether something is made up of just one pure material (substance) or whether it is a mixture of different materials.  Many materials that appear to be pure  are actually mixtures made up of two or more different substances.  Sometimes it is necessary separate the different materials in a mixture. Chromatography is one method that scientists use to separate mixtures.  Some mixtures of things like paint and ink contain two or more materials that each have their own color.  While these colors (dyes) are often hidden when the mixture is formed, they can be isolated based on the fact that each material in the mixture has its own unique properties.

Materials:

Filter paper or coffee filters       Black pens   Plastic cups              Scissors             Water

Exploration:

 In this activity, your job is to determine if different types of black ink are made up of a mixture of materials or just one pure substance. 

1) Set up two plastic cups on a level surface. Fill one cup with water to about1/2 inch from the top. 

2) Place one of the filter papers on a clean dry surface and locate the middle of the paper and poke a small hole in the paper. Using a black pen, make a series of dots around the hole as shown below in the first diagram.  Using a second piece of filter paper and a different black pen, make a series of similar dots.  

3)   To form the wick, fold a quarter piece of filter paper in half and then fold the filter paper in half again.  Fold it a couple of more times until it forms the “wick” that will be used for the experiment. Repeat this procedure to make the second wick.

4) Insert the wicks into hole next to the pattern of dots. Place the wick and the filter into the cup of water so that the wick extends into the water and the filter rests on top of the cup. Make sure that the rim of the cup is completely dry before completing this step. 

 5) Observe the ink dots as the water absorbs up the wick and across the filters. Record your observations on the data sheet. Pull it out of the water just before the water front reaches the edge of the filter.

Optional:

6) If time permits, create your own pattern of dots using multiple markers of different colors. Try to make the most colorful and creative pattern possible. After you're finished display the patterns in your room.  

Guiding Questions:  

1. According to your results, was the ink in your black markers made up of a mixture or was it a pure substance?

2. What do you think it was that caused the colors to separate from each other?

3. Do you think that most of the things on our planet our pure substances or mixtures? Explain your thinking. 

4. Name two things that we didn't discuss that you think are pure substances and two things that you think are mixtures.