RAINBOW IN A GLASS

You will need the following materials:

• four different colors of food coloring (e.g. red, yellow, green, blue)
• five tall glasses or clear plastic cups
• ¾ cup (180 g) of granulated sugar
• a tablespoon for measuring
• 1 cup (240 ml) water

In the first glass, add one tablespoon (15 g) of sugar. In the second glass, add two tablespoons of sugar, three in the third glass, and four in the last glass. Then add three tablespoons (45 ml) of water to each glass, and stir until the sugar is dissolved. If the sugar in any of the glasses will not dissolve, add one more tablespoon (15 ml) of water to all of the glasses, and stir again. When the sugar is completely dissolved, add two or three drops of red food coloring to the first glass, yellow to the second, green to the third, and blue to the last glass.

In the remaining glass we will create our rainbow. Fill the glass about a fourth of the way with the blue sugar solution. Next, carefully add the green solution to the glass. Do this by putting a spoon in the glass, just above the level of the blue solution. Slowly pour the green solution into the spoon, raising the spoon to keep it just above the level of the liquid, until the glass is half full. Add the yellow solution, and then the red one in the same manner. What do you notice about the colored solutions?

The amount of sugar dissolved in a liquid affects its density. The blue solution has the most sugar dissolved in it and is therefore the densest. The other solutions are less dense than the blue solution, so they float on top of it. The densities of the solutions should be very close however, and the solutions are miscible, so you will see that the layers do not form well defined boundaries as in the first experiment. If done carefully enough, the colors should stay relatively separate from each other. What do you think will happen if you stir up the liquids in the glass?