Chemistry in the Kitchen: Create Your Own Rock Candy
Image credit: Evan-Amos / Wikimedia Commons
If you’ve ever been to a candy store, there’s a good chance that you’ve seen what looks like colored crystal-like candy on a wooden stick. This is rock candy, and it’s not made from the rocks that you’d find in nature. Rock candy is made from crystallized sugar that forms in water. Anyone who has sugar, water, and a stovetop at home can easily make rock candy. Luckily, we’ve got some directions below so you can make them.
Be sure to have an adult present for this candy-making experiment as you’ll be dealing with hot liquids!
How to Make Rock Candy
Image credit: Tijana Drndarski / Unsplash
What you’ll need:
A wooden skewer OR a clean wooden chopstick
A clothespin
1 cup of water
2-3 cups of sugar
Optional: food coloring
A tall narrow glass jar
A pot for boiling water
An adult to help you
What you’ll do:
Position your clothespin on the wooden skewer so that when you place it into the tall glass jar and it hangs down, there’s about 1 inch (2.5 cm) of space between the skewer and the bottom of the glass.
Now place the clothes pin and skewer aside and find your helpful adult for the next steps that involve hot water.
Pour the cup of water into the pot and bring it to a boil on the stove top.
If you decide to use food coloring, add it to your pot and stir. The more you use, the darker your rock candy will be.
Pour about ¼ cup of sugar into the boiling water. Stir until dissolved.
Repeat step 5 until no more sugar will dissolve in the water. This part will take some time and patience, so it is important not to give up too soon.
Once no more sugar will dissolve, remove the pot from the heat and allow it to cool for at least 20 minutes.
While the water is cooling, dip half of your skewer in the sugar solution and roll it into some dry sugar. These are going to be your seed crystals and they will help jump start crystal growth. Let the skewer dry completely so the sugar crystals don’t fall off when you go to place it in the tall glass.
The adult can now carefully pour the cooled off sugar solution into the tall glass almost to the top.
Place the skewer into the tall glass. Use the clothespin to ensure that it is hanging straight down the middle and not touching the sides.
Allow the tall glass to fully cool off before placing it in a safe place where it will not be disturbed.
Be patient and wait. Sugar crystals should grow and appear over the next 3-7 days.
Image credit: Science Bob
The Science Behind Rock Candy: What Actually Happened During the Candy-Making Process?
When you make rock candy, sugar is added to hot water until a saturated solution is created. This is where sugar, called the solute, can no longer be dissolved into the water, called the solvent.
A supersaturated solution formed once the saturated sugar and water solution cooled down. This simply means that there is more of the dissolved solute (sugar) than could be dissolved by the solvent (water). This is a perfect environment for sugar crystals to grow.
Sugar will leave its liquid form and become a solid, growing on an item such as a wooden skewer. This method is called precipitation and when sugar does this, it is called a precipitate. As time passes during the 3-7 days of waiting for the rock candy to grow, the water will also evaporate (leave the solution and disperse into the air). With water leaving, the solution becomes even more saturated. The sugar molecules will continue to arrange themselves in an orderly fashion on the skewer and grow larger and larger until we can see cube-like crystals. This crystallization process is called nucleation. Your finished product will contain about a quadrillion (1,000,000,000,000,000) sugar molecules that have grown and attached themselves to the skewer! These molecules will be tasty, so enjoy!
Learn more about sugar and crystals.
If you’d like to see rock candy-making in action, you can watch this video from The Sci Guys.
By Megan Goldsmith
