Science is often referred to as the most fun subject in school mainly because… it is! It can be a most delicious subject, too. When you make this treat, you’ll be jumping “string-first” into some serious chemistry that’s hiding as candy. You’ll discover and use principles like solutes, solvents, viscosity, sedimentation, solutions, and supersaturated solutions. How tasty does all that sound?
How Does It Work
So, you dip a string into a solution of sugar and water and it seems pretty uneventful. It’s kind of like watching paint dry. How in the world did it turn into a beautiful crystal of candy on a string?
When you mixed the sugar with the water and then heated and stirred the solution repeatedly, you created a supersaturated solution. This means there are far more dissolved particles of solute (the sugar) than the solvent (the water) can normally dissolve and hold at a given temperature. By stirring the sugar in hot water instead of room temperature or cold water, the sugar is dissolved faster in the fast moving (heated) water molecules. As the water cools, the huge amount of sugar particlesremains in solution (a supersaturated solution) and it contains more sugar than can stay in the liquid. The sugar falls out of the solution as a precipitate (particles). These connect with other sugar particles, and a crystal begins to grow.
You gave the suspended sugar paticles a great place to begin crystallizing when you dried some crystals onto the string ahead of time. These are “seed” crystals. As sugar particles begin to settle (the precipitate), they join and form crystals quickly with other sugar molecules. You see this crystallization on both the bottom and sides of the jar as well as on the string. Sugar molecules continue to settle and crystalize on the string and on top of other sugar molecules until you pull it out of the solution and enjoy the candy.
