Step 1: Dip one end of the cake-pop sticks or wooden skewers in water and then roll them in sugar. The sugar should cover 2 to 3 inches (5 to 7.5 cm) of the sticks. Let them dry completely. These are the seeds for the sugar crystal growth.
Step 2: Boil the 2 cups of water and the 5 cups of sugar in a medium-sized pot until the sugar is dissolved as much as possible. It should look like syrup. Once cool, this is your supersaturated sugar solution.
Step 3: Let the syrup sit until it is no longer hot, and pour into glass containers. Add food colouring and stir.
Step 4: When the coloured syrup has cooled to room temperature, set the sugary end of the sugar-seeded cake-pop sticks or skewers into the syrup and let them sit for about a week. Gently move the sticks around occasionally, so they don’t stick to to the crystals in the bottom of the glass. If the glass container gets too full of crystals, pour the syrup into a new container and move your stick into the clear syrup to grow more crystals.
Safety Tips & Hints:
This experiment requires adult supervision for boiling and handing the hot sugar syrup. Once it’s cooled down, the kids can take over.
The Science Behind the Fun:
Like bricks in a wall, crystals are solids formed by a network of repeating patterns of molecules. Instead of the mortar that holds bricks together, the atoms and molecules are connected by atomic bonds.
Crystals that share the same chemical composition can be big or small, but the molecules always come together to form the same shape. Table sugar, or sucrose, is made up of a molecule comprised of two sugars, glucose and fructose. Crystals formed by sucrose are hexagonal (six-sided) prisms, slanted at the ends.
The crystals that make up your rock candy grow larger when the sugar molecules in the syrup bind to the seed crystals of sugar that you rolled on the stick in step 1.