Last updated 12-5-07
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Lab #15: Polymers
Preparing a Soil Substitute with Sodium Polyacrylate
Sodium polyacrylate is a polymer that soaks up 300 times its own weight in water. Its nickname is the Super Slurper. It is used in baby diapers to keep baby bottoms dry. It is also a more convenient way to provide water to animals during transporation. The water soaked polymer crystals won't spill, and animals can eat them to get water. Another common use is a soil substitute, which is what we will make in this experiment.

Let's begin with the items that you will need to get.

#1. Distilled water: You should already have some from previous experiments; however, this experiment will need about half a gallon. You could use tap water in this experiment but the manufacturer of the polymer recommends distilled water. Distilled water will make the polymer crystals grow larger. It's your choice.

#2. Small Plant: You will need a small plant to transplant to the polymer soil. Or you could use a cutting from another plant, or use a sweet potato or regular potato that will grow from one of its "eyes."

 

#3. Funnel, colander, or sieve. Your kit has a funnel. You can use any of these to help drain off excess water from the water soaked polymer crystals.
#4: Pitcher/Container. You need a container that can hold about 1/2 gallon of water. You can use the same container or get a smaller one for the one that will hold the crystals and the plant. The smaller one needs to be at least one quart. The one that is used to hold the plant and water crystals needs to be clear.
The following items should be in your chemistry kit.

#5. Two tubes of sodium polyacrylate: You have two test tubes filled with sodium polyacrylate.

The formula you see is that of sodium acrylate. The brackets indicate that it repeats itself into a long chain. That's when it becomes sodium polyacrylate.

A variation of this polymer makes plexiglass and acrylic paint.

 

#6. Food coloring & Plant Food: Your kit contains both of these. You may have a different color of food coloring.
Instructions Lab #15: Polymer Soil
Fill beaker about 7 times and transfer to the 1/2 gallon pitcher (container). Or pour distilled water straight into the pitcher. Or instead of distilled water...
Or instead of the distilled water, you can use tap water. Fill your 1/2 gallon container to mostly full. I was at my mother's when I did this experiment, and I didn't have my distilled water with me, so I used tap water.
Pour the entire contents of your vial of plant food into the water. Stir.

If you want to make some instant snow, grind up some of the crystals with the mortar and pestle in your kit. Put the powder in hand and add water.

Pour remainder of both vials of sodium polyacrylate into pitcher. Add the instant snow if you want. Stir again.

The crystals of sodium polyacrylate will start absorbing water and swelling.

 

(Take a picture at this point. See if you can set your camera to either 1600x1200, 1280x960, or 1024x768. If you own a 2 megapixel camera, just use the highest setting [3 stars].)

The manufacturer of the crystals says to wait 5 hours or longer for the crystals to reach maximum expansion. I found that in 2 hours expansion far enough along to go to the next step.

If the container you used to hold the crystals while they soaked up water doesn't have a pouring spout, pour everything into a pitcher or something with a spout.

Pour off the excess water. Here my mother is using the funnel. She had a sieve, but I wanted to see how the funnel worked.
Some crystals will slide out the pouring spout. The sieve, colander, or funnel will catch them. If your sieve, colander, or funnel gets full of crystals, pour the crystals back into the pitcher, and continue with draining off the unabsorbed water.

Now you are ready to transplant your plant. Or if you are using a sweet potato or potato, you can get it ready.

Place just a few (3) drops of food coloring in your sodium polyacrylate soil crystals. We put it just in the center, but you may want to mix it up.

Take a picture before you add your plant (or sweet potato)
Push plant down into the polymer soil.

My mother, Ida, felt it could use some glass swizel sticks as well.

She placed the plant on an end table in her living room. In 24 hours, she said the flower buds were starting to open.

Water will only need to be added to the sodium polyacrylate soil about 1/3 the time if it were soil. If the polymer "soil" shrinks by 20%, add more water. If you get more plant food, you can add a little of that, too.

Keep an eye on the plant and see how the roots do in this unusual soil.

Take at least one or two pictures after you get your plant into your container with polymer soil. One needs to have your face in the picture. If you had a helper, you can get his or her face, too, if you want.
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Since Feb 23, 2004