chapter 8
CRYSTALS
What do sucrose (table sugar), table salt, ice cubes, and diamonds have in common? They’re all made of crystals. Their molecules are locked together in regular shapes, like the way Legos lock together.
Some kinds of candy also contain crystals. Rock candy, which looks like clear colored blocks stuck together around a stick, is made of sugar crystals and food coloring. (The large sugar crystals make the blocks.) The sugar crystals in wintergreen Life Savers create flashes of light when you crush them. Chocolate bloom happens when the cocoa butter changes from one crystal form to another.
Some kinds of candy don’t contain crystals, like glassy Jolly Ranchers or chewy taffy. These candies are made with corn syrup. The corn syrup molecules come in different shapes that don’t lock together. This prevents crystals from forming. Oil is also added to candy to prevent crystals.
In this chapter, you’ll learn how to make crystals with different kinds of candy, and what kind of candy will never crystallize.
To dissolve the candy for these experiments, you’ll need to heat it in water. Ask a grown-up to help you because these mixtures will be very hot.
Time: About 1 week
Skill Level: Get a grown-up
Rock candy is made from sugar crystals. Here’s how you can make sugar crystals at home.
What you need:
Table sugar
Water
Small microwave-safe bowl
Microwave
String and a pencil (optional)
What to do:
1 Mix 2 tablespoons of sugar with 1 tablespoon of water in the bowl.
2 Microwave for 15 to 30 seconds, or until the sugar dissolves.
3 Optional: Tie a short piece of string to a pencil, and lay the pencil over the bowl so that the string dangles in the water. The crystals that form on the string will be easier to see.
4 Wait for several days and watch for crystals.
What’s happening:
When table sugar (sucrose) dissolves in water, the sucrose molecules separate and mix with the water. As the water evaporates, the sucrose molecules get closer to each other, and lock together to form crystals.
Store-bought rock candy made from sugar crystals.
Top: Growing sugar crystals. Bottom: Sugar crystals on a string.
Time: About 1 week
Skill Level: Get a grown-up
Some kinds of candy are made almost completely from sucrose (table sugar). Can you turn these candies into crystals?
What you need:
Altoids or mint Life Savers (crushed)
Water
Small microwave-safe bowl
Microwave
String and a pencil (optional)
What to do:
1 Mix 2 tablespoons of crushed candy with 1 tablespoon of water in the bowl.
2 Microwave 15 to 30 seconds, or until the powder dissolves.
Optional: Tie a short piece of string to a pencil, and lay the pencil over the bowl so that the string dangles in the water. The crystals that form on the string will be easier to see.
3 Wait several days and watch for crystals.
What’s happening:
Mint Altoids and Life Savers are made mostly from sucrose, the kind of sugar you find in your kitchen. When the candy dissolves, the sucrose molecules separate and mix with the water. As the water evaporates, the sucrose molecules get closer to each other and lock together to form crystals.
Pea-size sugar crystal made from Altoids.
more fun
If you taste the crystals, you’ll be surprised to find that they aren’t as minty as the original mints. When the flavor molecules bump into the growing sugar crystals, they don’t stick together very well. Eventually the flavor molecules are replaced by sugar molecules, which lock onto the crystal much better. This makes the crystals taste like plain sugar rather than mint.
Time: 2 to 5 days
Skill Level: Get a grown-up
You can make crystals out of candy made mostly from sucrose (table sugar). Can you make crystals from any other kind of candy?
What you need:
8 Pixy Sticks or 2 small rolls
of Smarties (crushed)
Hot water
Small microwave-safe bowl
Microwave
String and a pencil (optional)
What to do:
1 Mix the powder from the Pixy Stix or Smarties (about 1 tablespoon) with 1 tablespoon of hot water in the bowl.
2 Microwave for 15 to 30 seconds, or until the powder dissolves.
Optional: Tie a short piece of string to a pencil, and lay the pencil over the bowl so that the string dangles in the water. The crystals that form on the string will be easier to see.
3 Wait several days and watch for crystals.
What’s happening:
Pixy Sticks and Smarties are made from a kind of sugar called dextrose (glucose). This kind of sugar also forms crystals. You might notice that these crystals don’t look like table sugar (sucrose) crystals. Sucrose molecules and dextrose molecules look different, and they fit together in different ways. So sucrose crystals and dextrose crystals also look different.
Why do the crystals “crawl” up the side of the bowl? When the dextrose molecules start to crystallize, the first crystals form at the edge of the bowl. The dextrose water is attracted to these crystals. It seeps up into them, just as water seeps up the cotton candy in the Defying Gravity with Cotton Candy Slime experiment. When the water dries, the leftover dextrose forms new crystals on top of the old ones, making a crystal formation that looks ready to explode out of the bowl.
more fun
Although the crystals have formed, there’s still water mixed with them. Weigh your crystal bowl every day to see how much water has evaporated.
When the crystals are completely dry, smash them with a spoon and use the powder for the Candy Water Cooler experiment.
Time: 1 week
Skill Level: Get a grown-up
Candy made with table sugar or dextrose will form crystals. Can you make crystals with every kind of candy?
What you need:
Hard candy that contains
corn syrup, such as a lollipop
or Jolly Rancher
Hot water
Small microwave-safe bowl
Microwave
What to do:
1 Crush the hard candy.
2 Mix 2 tablespoons of the candy with 1 tablespoon of hot water in the bowl.
3 Microwave for 30 seconds, or until the candy dissolves. (Caution: hot!) Stir, and remove any lumps that won’t dissolve.
4 Wait for several days, up to 1 week. Your solution should thicken without forming crystals.
What’s happening:
Crystals can make candy grainy, so some kinds of candy must be made without crystals. Because of this, candy makers often add corn syrup. The different molecules in corn syrup don’t lock together, so the corn syrup prevents crystals from forming.
Will dissolved Jolly Ranchers ever form crystals?
