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!
• 1 cup water
• 2 cups sugar
• Glass jar or cup
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.