This is a hands-on science activity is great to keep the kids busy while school is out! It’s a tasty activity for the little ones in your life – just be sure to wash your hands first!
Supplies You’ll Need:
- Coffee Filter
- A Tall Glass
- Aluminum Foil
- Table Salt
- An Empty Bottle (2 Liter)
- A Ruler
- A Pencil
- Cut the coffee filter paper into a square that measures 3 inches by 3 inches.
- Next, draw a line with the pencil that is approximately 1/2 an inch from one edge of the paper.
- You will then make six dots with the pencil that are equally spaced along the line. Space the dots apart by approximately ¼ inch between the first and last dots. This should be the distance between the edges of the paper and the dots as well.
- Next pick out six different color Skittles. You will then need to label each of the six dots on the paper to represent the colors you chose. For example, R for red, G for green, Y for yellow etc.
- Next take an sheet of aluminum foil and cut it to be 8 inches by 4 inches. Lay it flat on a table.
- Using the pipette, place six drops of water spaced evenly along the foil. You will then place one color of candy on each drop. Remove the candies once the color come off of the Skittles and dissolved into water.
- Dip the tip of one of the toothpicks in one of the colored water. Lightly touch it to the corresponding labeled dot on your coffee filter paper (ie: If it was a yellow skittle, dab the toothpick on the yellow dot). Be gentle so that the dot of color stays small and so that the toothpick does not pierce the paper.
- Using a different toothpick for each color, repeat the above step for each of the remaining colors.
- Once all of the spots have completely dried on the filter paper, repeat the above two steps with the toothpicks to get more color on each spot. Repeat this 3-4 times while allowing the dots to dry in between each round.
- When the paper is dry, fold it in half so that it stands up on its own. Have the fold standing vertically so that the colored dots rest at the bottom.
- This next step is where you will make the “developer solution”. Add approximately ⅛ of a teaspoon of salt and three cups of water to a clean 2 liter plastic bottle. You will need to shake the contents of the bottle to dissolve the salt, so secure the bottle’s cap back to it and then shake. Once the salt has dissolved completely, your salt solution is ready.
- Pour the salt solution into the tall glass so that it fills about ¼ of an inch. The salt solution should be lower than the dots when you put the paper into the glass. Pin the filter paper to the glass with the clothespin. Again, the dots should be at the bottom.
- Wait and observe. When the salt solution is about ½ inch from the top of the paper, you may remove the paper from the solution and lay it out on a table to dry.
What is happening?
You’ll notice that the salt solution that initially was below the paper has now climbed up the paper. As we learned in previous lessons, gravity ensures that objects – like liquids – stay close to the Earth’s surface. The salt solution is able to move up the paper through a process known as capillary action – the same process that trees use to suck water up into their leaves.
You’ll also notice that as the saltwater climbed the filter paper, so did the individual color spots! There might even be a few that have separated into different bands of colors. In the case of multiple bands of colors for certain dots, it is because the colors of some Skittles are made from more than one dye. The salt solution allows for the individual colors of that Skittle to separate as the bands move up the paper. There are also multiple bands because of some of the dyes being more soluble in the salt solution than others. The ones that are not soluble will “stick” to the filter paper. The ones that are soluble will continue to travel up the paper. As a result, the colors that represent the different dyes will travel the filter paper at different distances.
This entire process is called chromatography. The salt solution is called the mobile phase because it is the portion of the experiment that allows for the dyes to move. The paper represents the stationary phase because it represents the medium that the dyes travel across. If a certain dye does not travel as far as a distance up the filter paper, it means that the dye has a greater affinity for the stationary phase. Dyes that traveled the furthest and were more soluble had a greater affinity for the mobile phase.
- Capillary Action – (n.) ability of a narrow tube (or a material matrix) to draw a liquid upwards against the force of gravity.
- Soluble – (adj.) (of a substance) able to be dissolved, especially in water.
- Chromatography– (n.) a process of separating out different parts of chemical mixtures onto an absorbent material to be later analyzed.
- Stationary Phase – (n.) the solid or liquid phase of a chromatography system on which the materials to be separated are selectively adsorbed.
- Mobile Phase – (n.) the phase of a chromatography system that carries the components of the mixture through the medium being used.