Introduction

Scientists must be good observers who carefully watch the events that occur when they do experiments. Sometimes they create unusual new substances that can act in strange and cool ways. Ghost crystals are made from a substance called sodium polyacrylate that acts in a weird but very useful manner. Although these are just tiny crystals right now, they will change over night if you place them in a glass of water. These modified crystals will have some cool and unique qualities and they are very useful for a variety of purposes.

Materials: Clear plastic cup, water, 10-15 ghost crystals, spoon, small plate or bowl, thread (optional), pin or toothpick(optional).

1. Place your ghost crystals into a cup of water and watch for the next few minutes. Write down what you see happening on the lines below.

3. The next day, look at the glass carefully without touching the water. What do you see? Write down what you see on the lines below.

4. Now take a spoon and slowly stir it around in your glass a few times. What does it feel like while you are stirring? What do you think has happened to the ghost crystals? Write down what you think has happened.

5. Now spoon out some of your ghost crystals onto a plate or bowl and observe how they have changed. The crystals grow more than 100 times their starting size. What do you think happens that lets them grow so big?

6. Next, using the thread provided tie up your ghost crystal using a single loop around the largest part. This is difficult and takes some practice as the crystals are very fragile. Choose the largest crystals you can find and keep trying until you get it. Your teacher may have to do this part for you.

7. Carefully pick up the crystal by the thread and dip it into a clean glass of water. What do you observe? Cool huh. Now place in the water and show the crystals to some of your friends in the class.

8. Now comes the tricky part, take your crystal and stick a pin or a toothpick carefully straight through it. Now the sight is especially strange, for the pin seems suspended in the middle of the loop with no visible means of support.

9. You are now done with the lab portion of this assignment. You can keep the crystals in the water or let them dry out and re-use them (but be patient, it takes a long time).

2. What do you think happened to the ghost crystals that caused them to change (grow) so much?

3. Now that you have seen what the ghost crystals are like, what do you think that we could use them for? Describe at least three possible uses.

Bring the class back together and discuss their ideas regarding the ghost crystals. Focus the discussion on the importance of making good observations and the understanding that substances can change in remarkable and often very useful ways.

This is a great activity to do when you are talking about the importance of making good observations of the world around us. When students first look to see what has happened to their crystals, they often think that they have dissolved or disappeared. Some may notice that there are some tiny bubbles that aren't escaping to the top of the glass and occasionally you can see a vague outline of the crystal. When they stir the cup, they can feel that there is something there besides that water.

Ghost crystals are made from a substance called sodium polyacrylate - a large polymer molecule that is made up of repeating units. The grown ghost crystals are nearly invisible in water because they are made of about 99.5% water and so they don't bend (refract) the light that goes through them. Over a period of several hours they absorb hundreds of times their own weight in water acting like an extremely flexible water balloon. The water initially moves into the crystal because there is a higher concentration of water on the outside than there is on the inside and substances always move from where they are more to less crowded. These water absorbing crystals are put in dirt to help new plants survive while they grow a good root system. The crystals absorb water when it rains and then let it go a little at a time as the dirt dries out. This helps the plant to make it through the hot dry summer.

Teacher Notes: Although ghost crystals are non-toxic they should not be eaten and should be handled with care. They are safe to touch but should be kept away from your eyes. You can let the crystals dry out and then recycle them if you want and otherwise they can be disposed on in the trash.

Student activity sheets should be evaluated to check for student understanding. A rubric for this activity can be found at the following link: Activity Rubric