Experiment Details

• Grade Level: 4th–7th Grade (adaptable K–8)
• Key Topics: Saturation, Crystallization, Evaporation
• Estimated Time: Setup: 20 min; Crystal growth: 5–7 days
• Mess Factor: Low to medium (sticky spills possible!)

Purpose: To observe how crystals form from a saturated sugar solution as water cools and evaporates.

Hypothesis: If I dissolve lots of sugar in hot water and let it cool slowly, then sugar crystals will grow on the string because the water can’t hold all the sugar.

Step-by-Step Instructions

1. Carefully measure 2 cups of water and pour it into the saucepan.
2. Heat the water over medium heat until very hot (not boiling). Use a pot holder for safety.
3. Slowly add 4 cups of sugar, stirring constantly until it completely dissolves. You want a saturated solution—no more sugar can dissolve!
4. (Optional) Add a few drops of food coloring and stir gently.
5. Let the sugar solution cool for about 10 minutes.
6. Tie one end of the cotton string to the middle of the wooden skewer or stick.
7. Wet the string and roll it in sugar to “seed” it and help crystals form.
8. Place the skewer across the top of the jar so the string hangs down into the solution without touching the sides or bottom.
9. Use a clothespin or tape to hold the skewer in place.
10. Set the jar somewhere safe where it won’t be disturbed.
11. Check each day to observe crystal growth. Wait 5–7 days for large, visible crystals.
12. When the crystals look big enough, carefully remove the string and let your rock candy dry on a paper towel. Enjoy!

Results & Scientific Explanation

As water evaporates and the solution cools, it becomes “supersaturated”—holding more dissolved sugar than it can keep. Sugar molecules begin to bond together, forming crystals on the string where they have something to “grab onto.” The result: big, sparkly sugar crystals you can eat!

• Saturated solution: Hot water can dissolve more sugar than cold water.
• Evaporation: As water leaves, sugar comes out of the solution as solid crystals.
• Crystallization: Sugar molecules arrange in a repeating pattern to form crystals.

Real-World Connection: How Are Crystals Made?

The same process forms crystals in nature—like salt, snowflakes, and gemstones! In factories, rock candy is made by letting sugar solution evaporate in huge tanks, growing edible crystals on strings or sticks.