Posts Tagged ‘safe’

Liquid or Solid?

November 1, 2008

This project is easy, non-toxic and so much fun that it is worth every bit of the mess it makes.   Your kids will love it and it is easy to clean up. 

All you need is a cup of cornstarch and half a cup of water.  Let your child measure everything out.  (He or she will enjoy it much more than you will.)  Simply add the two ingredients to a medium-size bowl and let your child mix them together with a spoon or their fingers.

Then, play with it!  You will discover that it behaves like a solid when you agitate it, or move it quickly,  and like a liquid when you let it sit still.  Pour some onto plates or into bowls if you want to.  We just poured it directly onto our table which was pretty messy, but lots of fun!  Hold a handful on your palm and watch it drip between your fingers!  Have your child roll it into a ball.  If it gets too dry, just add a little more water.

Cornstarch molecules are like long ropes.  When you leave them alone, or move them slowly, they can slide past each other and look like a liquid.  However, if you squeeze them, stir them or roll them around in your hands, the ropey molecules get “tangled up” and they look and feel more like a solid.

Have fun! (Click here to see my video on how to make cornstarch goo.)

Mad Scientist’s Green Slime

September 27, 2008

With Halloween just around the corner, what could be more fun than creating your own green slime to play with?  You can synthesize your own slime using only Elmer’s glue (the non-washable kind), Borax (found in the laundry detergent section of most stores), green food coloring and water.  It would be a great activity for a Halloween party!

It’s fun to find an old white, button up shirt for your child to use as his or her “lab coat”.  Not only will it make them feel like a scientist, but it will protect their clothes.  You could try to find some old goggles in your garage for your child to wear for fun too!  In a bowl, have your child mix together about 1/3 cup glue and 1/3 cup water with a spoon or Popsicle stick.  These measurements don’t have to be exact.  Add a few drops of green food coloring and mix well. 

To make the Borax solution, add around a cup of water to a jar.  To the water, add about a Tablespoon of Borax.  Have your child shake the jar to dissolve as much of the Borax as possible.  You are making what is called a saturated solution, so it may not all dissolve!  Don’t worry, it will work just fine.

Have your child add about a teaspoon at a time of the Borax solution to the glue/water mix.  After each addition, have them stir the mixture together.  You should see long strings begin to form and stick together.  Keep adding Borax until the mixture doesn’t feel gluey any more.  It will form sort of a shiny playdough-like substance.  If you add too much Borax solution, it will feel wet.  You should be able to just knead it a little to absorb the extra water!  The slime is not toxic, but Borax is soap, so don’t let your kids eat it!

I am a biologist and not a chemist, but here is the science, as I understand it. 

Mixing Elmer’s glue with water forms a substance called a polymer, which is a long chain of molecules.  (A molecule is the smallest amount of a specific chemical substance that can exist alone, like H2O, a single water molecule).  The polymer formed by water and glue is called polyvinyl acetate. 

The Borax solution (sodium tetraborate) is a cross-linking substance that makes the polymer chains stick together.  As more and more chains stick together, they can’t move around and the goo gets thicker and thicker.  Eventually, all the chains are bound together and no more Borax solution can be incorporated.

You can store the slime in plastic bags.  If you want to make a larger batch, just remember to mix equal amounts of glue and water and add as much Borax solution as needed.  Have fun!