How To Teach Science… With Candy (Part 4)
You’ve learned how important crystals are to the creation of hard candies like butterscotch and peanut brittle and soft candies like fudge, but are there any times when you would want a candy without ANY crystals at all?
Well, the candies I just mentioned all have one specific property about them (and it’s not their simple ingredients of sugar and water.)
Can you guess what it is?
If you said that you can’t see through them (which is what scientists call opaque “oh-pay-kuh”) you are correct! The opposite of being opaque is to be transparent. Objects that are transparent, like windows, allow light to travel through them very easily. And since I’m throwing around some scientific terms, let’s review some basic concepts about science that may come in handy this week:
Light cannot easily pass through most candies that are formed from crystals. The crystals tend to get in the way of the light passing through the candy and block it from traveling through. This makes an object opaque.
MAKING EDIBLE GLASS
The texture of transparent candy is much different than the other hard and soft candies we have explored so far. The trick to make this type of candy is to first boil off most of the water within your sugar syrup. Yep! You want all of those ATOMS inside water to absorb as much heat energy as you can so that they will evaporate into the atmosphere!
By removing so much water from the syrup, you have increased the DENSITY of sugar molecules within the solution.
THIS IS GOOD! REMEMBER – THE MORE WATER A SYRUP CONTAINS, THE SOFTER THE CANDY WILL BE
You’ve never seen a SOFT glass before right? No way! This type of candy is going to look AND feel like glass! So you need as much water out of that solution as possible.
After making your sugar solution incredibly hot, the next step is to keep the sugar molecules from sticking together and forming crystals.
You may believe that the formation of crystals means that something new is being created within the solution. However, if you have been following this blog for any period of time you would know that this does not happen! ATOMS cannot be created (or destroyed) during the formation of crystals. The LAW OF CONSERVATION supports this beautifully! All that is happening is the rearranging of ATOMS within the solution into a crystal structure! Okay, back to the candy…
Any crystals at all will cause this molten mass of sugar to turn into an opaque mess very quickly!
In order to keep these sugar molecules from binding together you have to DIFFUSE their energy away as quickly as you can!
This means you have to lower its temperature very very quickly. If you don’t lower the temperature fast, the molecules will slow down and move into each other. This is bad! As they slow down, they start to stick to each other, and this is how crystals are formed.
Since crystals are made up of several sugar molecules bound together, they are large enough to block light as it passes through the candy. This causes the candy to be opaque. (I know I already said that once in this post, but it is very important to the next few lines…)
However, when you cool a sugar solution really fast, the sugar molecules get “stuck” in the cooling fluid and do not have the energy to move around and bind to each other. And, since sugar molecules are so tiny, light does not bounce off of them. This makes the candy transparent.
By the way – this is almost exactly how people make sheets of glass! Naturally, the windows on your home are not made of sugar molecules (please don’t go around the house licking your windows.) Instead, a molecule called silicon dioxide is melted, poured, and its temperature lowered to create most of the glass that we typically find in our homes!
Movie makers have known about this property for YEARS! In fact, it is a pretty good guess that the majority of bottles and windows that are broken over actors within the movies are made from this rapidly cooled syrup!
By the way, I’m still waiting to see the outtakes at the end of a movie where an actor starts sucking on a broken piece of “candy glass.” I know it will happen someday…
Learn more about chemistry concepts (and many more) in the Classic Science: Series for the Family and be certain to come back every Thursday or subscribe to The Blog of Mr.Q to learn more about how to teach science during breakfast, lunch, and dinner!
