August At-Home STEAM Activity: Growing Sugar Crystals

When you boil 2 cups of sugar with only 1 cup of water, you create a supersaturated solution. In a supersaturated solution, there is more solute (sugar) than the solvent (water) should be able to dissolve. By heating the mixture, however, you force more sugar to dissolve in the water than would be possible at room temperature. The resulting solution is unstable, but completely liquid!

As this heated sugar solution cools and rests, the sugar cannot remain dissolved as a liquid. Instead, the sugar comes out of solution and forms solid crystals in a process known as precipitation. Sugar crystal precipitation intensifies over time as water begins to evaporate, making the solution even more concentrated and unstable.

The key to growing sugar crystals on a string is creating “seed crystals.” When you first dip your string into the solution and remove it to dry, you are allowing tiny sugar crystals to form on the string. As sugar begins to precipitate out of solution, it prefers to form crystals where crystals already exist. Since you already created “seed crystals” on your string more crystals will form there!

Materials:
• 1 cup water
• 2 cups sugar
• Glass jar or cup
• Pencil
• String

Procedure:

1. Stir together the water and sugar.
2. With an adult’s help, heat the sugar solution until boiling, stirring occasionally. Then transfer to a glass jar to cool.
3. Tie the string around the pencil.
4. Dip the string into the sugar solution then remove it to dry overnight. Save the sugar solution. 5. The next day, hang the string in the sugar solution, ensuring it is submerged and does not touch the jar.
6. Allow sugar crystals to grow undisturbed for 7 days before removing.

Additional Exploration:

• Spice up your crystals with food coloring or an extract like vanilla or almond.
• You can eat your sugar crystals! However, if you plan to eat them, we recommend growing sugar crystals on a cotton string or wooden craft stick.

Questions to Ask:

• Why do you think the string needs to dry overnight after being dipped in the sugar solution the first time?
• What would happen if you swirl the mixture every day instead of letting the crystals grow undisturbed?
• After removing your sugar crystal creation, what does the remaining sugar solution look like in the jar?