Rock candy is a sweet science project that lets you watch crystals grow day by day. You start by mixing lots of sugar into hot water until the water cannot hold much more sugar. As the syrup cools and sits still, sugar leaves the water and builds shiny crystals on a wooden skewer.
This project matters because it shows how solids can dissolve, move in a liquid, and form repeating crystal shapes.
Key Facts
- A common recipe is 3 cups sugar + 1 cup water to make a very sugary syrup.
- Hot water dissolves more sugar than cold water.
- A saturated solution holds as much dissolved sugar as it can at that temperature.
- Crystals grow when sugar particles leave the syrup and attach to the skewer.
- Rock candy usually needs about 7 days to grow large visible crystals.
- Growth time example: 1 week = 7 days = 168 hours.
Vocabulary
- Crystal
- A crystal is a solid with tiny particles arranged in a repeating pattern.
- Dissolve
- To dissolve means to mix into a liquid so the solid seems to disappear.
- Solution
- A solution is a mixture where one substance is spread evenly through another, such as sugar in water.
- Saturated
- A saturated solution has as much dissolved material as it can hold.
- Evaporation
- Evaporation is when liquid water slowly changes into water vapor and leaves the mixture.
Common Mistakes to Avoid
- Using cold water, because cold water cannot dissolve as much sugar and may make fewer crystals.
- Not adding enough sugar, because the syrup may not become saturated and crystals may grow slowly or not at all.
- Letting the skewer touch the bottom or side of the jar, because crystals may stick to the glass instead of growing neatly on the skewer.
- Shaking or moving the jar every day, because the growing crystals are fragile and can break off before they get large.
Practice Questions
- 1 A recipe uses 3 cups of sugar for 1 cup of water. How many cups of sugar are needed for 2 cups of water?
- 2 Rock candy grows for 7 days. How many hours is that?
- 3 A student stirs sugar into hot water until no more sugar will dissolve, then lets the jar sit quietly. Explain why crystals can grow on the skewer as the syrup cools and waits.