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COLORING WITH SOLUTION IN SUSPENSION

This time we will pretend we are chemists. Who knows? We might even learn something!

For this project we need three plants that are alike or of the same type, three test tubes, some red ink (we can get that from the school's bookkeeper!) and a substance called "Congo red." Since I didn't know what Congo red is, I thought maybe we'd all get to go to Africa, because that's where the Congo is. The more I thought about it, the more silly it seemed, so I asked Mr. Webster what is "Congo red?"

Congo dye is "any of a group of direct azo* dyes, most of which are derivatives of benzene." Congo red is a "Congo dye used in dyeing cotton and wool red, and as an indicator, either in solution or on test paper, being turned blue by acids. (cf. litmus.)" Azo* dyes contain "two nitrogen atoms, attached on each side of carbon." Now you know everything Mr. Webster knows about Congo dye.

We already know about litmus. Litmus paper is a little strip of paper that has been treated with a chemical. It is used to test the acidity/alkali of solutions, such as the water in an aquarium. If there is too much acid, the paper turns blue. On the side of the box in which the litmus paper comes, there is a graph of different shades of blues and greens, with numbers beside it. To test the aquarium water, you would dip the strip of litmus paper into the water, and wait a few minutes until the color develops. Then compare it to the colors on the side of the box, and it tells the pH of the water, so you know whether it is safe for the fish. According to Mr. Webster, "litmus paper" should really be called "Congo paper."

For the project, we will put water into one test tube, red ink into another, and into the third test tube, we'll put Congo red. Congo red does not dissolve when it is put into water. The particles are "suspended," or "in suspension," which means the particles just float around in the water, but do not melt into the water, or mix with it. If you put some sugar into a little water, the sugar would melt and there wouldn't be any grains of sugar in the water, but the water would be kind of like syrup. If you put pepper into a little water, it would just float around in the water, and would not melt. Congo red does the same thing as pepper. You see, we have learned something!

Since this kind of project works really well with daffodils and daisies, we'll use whichever one is in season. We don't really need to put in the whole plant--just put one cut flower with a long stem, and a few leaves, into each test tube. Mark the calendar on the date we began this experiment. After a few days, we want to check the plants,
especially the blossoms, and see if there is any red color in them. Well, it is plain to see that the tube with water in it has not changed the flower; of course the flower and
leaves would have drooped and dried up without the water. The flower and leaves in the tube with red ink have changed a great deal, haven't they! Look closely at the tiny veins in the flower and leaves. We can really see them now, with the red ink traveling through them! The edges of the flower petals are all red, too!

Now for the part for which we learned so much. What changes do you see in the flower and leaves that were soaking in the Congo red? None? How can that be? This plant has veins just like the other two. It's sitting in red stuff. It didn't dry out and droop, so we know it took in the water. But there are no little red lines in the leaves or the blossom!

Let's try a quick experiment, using water, sugar, and pepper. Mix 1/2 teaspoon of hot water with 1/2 teaspoon of sugar, and stir. Pour it onto a folded paper towel, and put it aside for awhile. While it is sitting, mix 1/2 teaspoon of hot water with 1/2 teaspoon of pepper, and stir. Pour that onto a folded paper towel, and that, too, can be put aside. When the paper is dry, we will see that the paper towel with water and sugar on it has absorbed the water and sugar--the paper is kind of stiff, and if we put a tiny drop of water onto it, it will be sticky. If we lift the paper towel with water and pepper on it, the pepper just falls off the towel, in the same little chunks it was in when we mixed it with the water. Probably the Congo red didn't melt into the water, just like the pepper didn't dissolve. The Congo red was not "in solution;" it was "in suspension." The other part of this that we must understand is that plants, just like paper towels, cannot take in and absorb particles (suspension), like it can take in and absorb liquid (solution). From this we can extrapolate (one of my favorite words, pronounced "ex- TRAP-oh-late", meaning to guess that if one thing is true, something like it might also be true) that if you wanted to put fertilizer onto your plants to make them grow bigger, or stronger, the fertilizer has to be something that will melt into the water so that the plant can take it in and absorb it.

 
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