Friday, May 27, 2011

Ice Bags--Frozen Fireworks?

On the day we experimented with M&Ms and Ziploc bags of ice to learn about cold water currents, my son and daughter decided to fill baggies with water and put them in the freezer. (Note to self--no wonder I'm out of sandwich bags!)








When I cleaned out the freezer, hoping to sneak the water bags into the garbage, I was amazed by what I saw. Air bubbles had formed lines streaking out from the center of the ice, as if we'd frozen a firework explosion.

The explanation for this phenomenon has to do with the air in the water.  PhD Martin Lersch writes in his food chemistry blog, Kymos, that room temperature water has air dissolved in it, and the amount of air it can hold increases as it gets colder.  (I had to boil water to remove the air for my experiments with floating conversation hearts.)  When the water freezes, "the water can no longer keep the air dissolved and a bubble is formed."  If the ice were to freeze from the inside out, the air could escape naturally.  However, since freezer ice freezes from the outside in, and (presumably) since our ice was enclosed in air-tight Ziploc bags, the air was trapped inside the ice.  We froze the water in large amounts, which contained more air than regular ice cubes.

The result?  Lots of trapped air bubbles forming slow-motion fireworks, a beautiful reminder of Nature's inexhaustible designs.

Friday, May 20, 2011

Egg Decorating

Whenever we do major candy experiments, I end up with stained countertops. So, this Easter, I thought we should try dying Easter eggs with candy.

The Laffy Taffy looked pretty good when it was stuck on the egg. However, when we peeled it off, only one egg had any color left.



We'll have to try better ways to transfer color next year when it's egg season again.

Wednesday, May 18, 2011

Pixy Stix Art

A new use for Pixy Stix: sand art.

Pixy Stix After the Art

Of course, after you've opened all those Pixy Stix you have to do the acid test. (Pixy Stix are awesome to test, since they dissolve so fast.

Trying something new, my daughter mixed the baking soda with the Pixy Stix while the powder was still dry.

Then we poured in the water. Great bubbles!

Sinking Hearts, Rising Hearts

What do romance novels have in common with candy experiments?  They're both full of sinking and rising hearts.

Cake Mate hearts float nicely for a few minutes when you put them in water. As they do, they dissolve, shedding bright red sugar solution. The solution, denser than pure water, sinks.



Conversation hearts sink immediately.  In some hearts, however, trapped air bubbles seem to emerge, floating upwards, sometimes carrying up candy particles.  (Watch the blue heart in the right side of the bowl shedding pieces which float up to the surface.)



I can feel my heart rising already, can't you?

Sunday, May 8, 2011

Friday, May 6, 2011

Melted Gum

Note to self: next time I let my kids melt gum on a baking sheet, put down tinfoil!  I keep forgetting this tip I've seen my readers use, and it would save me hours of work.  I still haven't gotten all of the gum off.

Tuesday, May 3, 2011

Chromatography Methods

The theory of chromatography is simple: you dab a dot of color onto a paper, stand the paper up in water, and let the rising water separate the colors by solubility.  But how do you make sure the paper stays upright?

One easy method is to crease the chromatography paper vertically, then stand it in water.  This works especially well if the bottom of the paper is cut flat (an angled bottom will make the paper tip.)


If the paper doesn't stand on its own, try folding the top of the paper over the side of the glass.  Note that that this method is problematic: a professional biochemist cautioned me that surface tension between the glass and the paper might interfere with the capillary action causing the water to rise.  However, it works well enough for M&M color separation, or the other basic chromatography we do in our kitchen.  For better results, angle the bottom of the paper out so that the paper is not stuck to the glass.


If your chromatography paper is especially difficult to work with, clip it in place with clothespins or binder clips.  Lay a pencil over the top of the glass and clip on the paper, forming a T with the paper hanging down, or take a shortcut and clip it to the side of the glass, as shown (angling the paper out from the glass, as above).


When doing chromatography with large groups, I use clothespins on a wire rack to suspend the chromatography papers over a dish of water.  This way I only need one water container.  (Make sure your scientists label their papers in pencil if they want to know which are theirs.)



Whatever chromatography method you use, make sure that the color dot is placed above the waterline.  This is easy if you're hanging the paper--just hold the bottom edge in the water with the dot above the surface, then clip the paper in place.  If you fold and stand your paper, make sure the dot is high enough so that it will still be dry when you stand up your paper.  Then watch the water rise, and see what colors your dot is really made of.