Crystal Clear

The last couple of activities have talked about crystals, but what are they? Is a crystal just another name for a solid? And are all crystals the same?

Crystals are always solid, but not all solids are crystals. Glass and many plastics are examples of solids that are not crystalline. In a crystal, the atoms or molecules are piled together in a very neat, organized way, and they're often arranged in familiar shapes like these:The names may seem funny to you, but you probably recognize squares, rectangles, and hexagons. Each of the colored balls represents an atom or molecule. For example, table salt (sodium chloride) has a cubic crystal structure. Half of the balls are sodium atoms, and half are chlorines. These shapes are just building blocks. A real crystal would have zillions of these blocks, all exactly the same, all piled up one on top of another. Table sugar, or sucrose, is made up of monoclinic blocks, with the green balls representing individual sugar molecules.

When you made jack wax and nut brittle, you learned two ways to keep large crystals from forming - by cooling quickly, or by adding some other substance. Let's talk about why these methods prevent crystallization. Imagine that you're a young child again, trying to make a tower out of building blocks. It's easy to get the first few blocks in place, but then it gets harder. If you had to construct the tower very quickly, it would probably fall down sooner than if you could build it slowly because you would be able to place each block just where you wanted it. In the same way, cooling a liquid very quickly doesn't let big crystals grow. Now imagine trying to build a tower with some cubical blocks and some that had a triangular shape! This wouldn't work very well either, because it's harder to fit the triangles into your pile. So, adding a molecule of another shape (like glucose and fructose in corn syrup) also makes it hard for crystals to get big.

So, was this explanation crystal clear???

A Little Brittle

In the last experiment/recipe, you learned how to stop crystals from forming by cooling very fast. In this activity, you'll learn another way to prevent crystals. In the kitchen, "table sugar" usually means a molecule called sucrose, which is usually made from sugar cane or sugar beets. Corn syrup, on the other hand, contains other sugar molecules, called glucose and fructose. If you add these types of sugar to the sucrose, the glucose and fructose lead to "mistakes" when crystals try to form, and the result is - no crystals (or at least, not very many)!

This is a recipe for nut brittle, which uses corn syrup mixed with table sugar to keep crystals from forming. The presence of crystals would not change the taste of the candy, but would make it feel gritty in your mouth. Nut brittle is most commonly made with peanuts, but you can also make it with other nuts, if you don't like peanuts or can't eat them.

What you'll need:
1/2 cup light corn syrup
1 cup sugar
1 cup dry-roasted peanuts or other nuts
2 teaspoon butter
1 teaspoon vanilla extract
1 teaspoon baking soda
Salt (if you want)
Microwave oven
Large microwave-safe bowl
Spoon
Baking pan (10" x 10")
Oven mitts

Rub the baking pan with about 1 teaspoon worth of butter and put it aside. Mix the corn syrup and sugar in the bowl and microwave on high for 4 minutes. The sugar should have started to melt, but still be clear. Remove from the oven and stir in the nuts. Be careful - the bowl will be VERY hot. Microwave on high about 3 more minutes or until the mixture turns light brown. Take the bowl out of the microwave again and stir in the other teaspoon of butter and the vanilla extract. Microwave on high again for 1 minute. Remove the bowl again, and stir in the baking soda (what do you see happening?). Quickly pour the mixture into the baking pan and let it cool. When the brittle is safe to handle, slide it out of the pan, and break it into small pieces. If you're going to store it, make sure it's in an airtight container.

This recipe includes another chemical reaction that has nothing to do with sugars or crystals. When you added the baking soda, the brittle got cloudy because thousands of tiny gas bubbles formed. Where did they come from?? When baking soda is heated to 160^oF, it gives off carbon dioxide gas. The sugar/nut mixture is much hotter than this, so the gas is given off very quickly. The bubbles don't change the taste of the nut brittle, but do make the candy lighter and easier to chew.

Marvelous Maple Candy!

Do you like maple syrup on your pancakes or waffles? Then try this candy, which is sometimes called "Jack Wax" (although that name doesn't make it sound very tasty!). You'll heat the syrup, then pour it directly onto snow or ice, forming a taffy that can be formed into fun shapes. This recipe works best if you have fresh snow available, but crushed ice is OK, too. A couple of warnings - be very careful with the hot syrup, as it can burn you. Also, if you have braces or other tooth problems, maybe you shouldn't try this very sticky candy (check with an adult first).

What you'll need:
1 cup maple syrup (genuine syrup, not the artificial kind)
Large saucepan
Spoon
Fork
Small juice glass
Large bowl
Stove
Candy thermometer (optional)
Water
Enough snow or crushed ice to fill the bowl

Put the snow or ice into the large bowl. Fill the small glass about 3/4 full with water. Pour the maple syrup into the saucepan and heat to boiling. Once the syrup starts to foam, reduce the heat to low. Keep stirring. In the beginning, the syrup will create a LOT of foam as the water boils off. Be sure that it doesn't boil over onto the stove - remove it from the heat for a few minutes if necessary.

While the syrup is heating, you should test it by letting a drop fall from the spoon into the water in the juice glass. You'll notice that, at first, the drop loses its shape right away, but as the syrup gets hotter, it forms little balls that fall to the bottom. And these balls get tighter as the temperature goes up. Candymakers call these the thread stage, the soft-ball stage, and the hard-ball stage.

You'll need to keep heating for at least 10-15 minutes. If you're using a candy thermometer, you can stop when the syrup reaches 240^oF; this is in the soft-ball stage. If you don't have a thermometer, uses the water test described above. Then pour a little of the syrup over the snow or ice in a ribbon. It will harden and cool really fast. Use a fork to pick it up. If it is soft but stretchy, then the syrup is at the right temperature, and you should pour most of it over the snow. If the syrup stays mushy even when cooled, heat it a little longer. You can eat this candy mixed with the snow or ice, or save it for later. If you're saving it, put it in the refrigerator.

Pouring the syrup onto ice cools it quickly, and the solid candy is smooth and shiny, not bumpy like the rock candy was. The crystals in rock candy take time to grow. When the liquid is poured onto snow or ice, there is no time for the crystals to even get started, so the solid is smooth.

Candy Rocks!

Here's a way to make rock candy (don't worry - it doesn't actually contain rocks). Rock candy is made up of large sugar crystals grown on a string. This experiment will take a few days, but the results will be delicious!

What You'll Need:

Glass jar

Pencil or other thin piece of wood (long enough to fit across the mouth of the jar)

Cotton string with a rough surface

3 cups sugar

1 cup water

Pan

Stove

Spoon (plastic or wood is best)

Paper towel

Food coloring (if you want)

Cut a piece of string about 8 inches long. Tie one end around the pencil. Place the pencil across the mouth of the jar, with the string hanging down inside. The string should reach almost to the bottom of the jar, but shouldn't touch the bottom or sides. If it's too long, cut the string or wrap it around the pencil to shorten it. Put the pencil and string aside.

Put the water in the pan and boil it. When it is boiling, start to add sugar, about one teaspoonful at a time. Stir until the sugar dissolves completely, then put another teaspoon in and stir that until it dissolves. Keep adding sugar until it won't dissolve any more (you may use less than 3 cups). You need to get as much sugar as possible into the solution in order to get big crystals quickly. There shouldn't be any undissolved sugar on the bottom of the pan. If you want colored rock candy, add a few drops of food coloring at this time.

Carefully pour the sugar solution into the jar (remember that it's very hot!). Make sure that there are no sugar granules in this solution. Put the pencil over the mouth of the jar as before, and let the string hang down into the solution. Place the jar somewhere that it won't be disturbed. Cover it with a paper towel to keep dust out.

Now you wait! The shiny sugar crystals will grow slowly, and you should see them starting in a day or two. It will look something like the picture on the right. In about a week, you'll notice that the crystals aren't getting any bigger. That's when you can take them out of the jar to dry. Before you enjoy eating your rock candy, take a close look at it. What shapes do the sugar crystals have? Is this the same shape that the original sugar granules had?