Growing crystals with sugar

Growing crystals with sugar

My kids love experiments so there's no need to sweeten the deal with sugar but Ethan had seen a geode and and wanted to understand more about crystals so I decided on this experiment to show him crystal formation.

This sweet experiment helps kids to explore super saturated solutions, crystal formation and evaporation. Plus you get to make a tasty science treat!

Crystal making with super saturated sugar solution

Materials

Items for making sugar solution crystals

  • Wooden skewer
  • Peg
  • 1 cup water
  • 2-3 cups sugar
  • Tall narrow glass/jar
  • Food colouring (optional)

Method

  1. Pour the water into a pan/saucepan and bring to boil.
  2. Pour around 1/4 a cup of sugar into the water and stir until it has dissolved.
  3. Repeat step 2 until no more sugar will dissolve. Be patient however because the sugar will take longer to dissolve each time.
  4. Add 4-8 drops of your favourite food colouring if you wish.
  5. Once no more sugar will dissolve, remove mixture from the heat and set aside for 20-30 mins to cool.
  6. While it’s cooling, dip half the skewer into the mixture and then roll in some loose sugar, also leave this to cool. This will help jump start crystal growth.
  7. Place your skewer in between the peg and have it hang down into the jar. Make sure the skewer does not touch the sides and make sure it is around 3cm from the bottom of the jar.
  8. Carefully pour the sugar solution into the jar, almost all the way to the top.
  9. Set the jar aside. Within 3-7 days a delicious rock candy treat will have formed!

Super saturated sugar solution for making crystals

The Science

The skewer provides a surface for the crystals to grow on. By wetting the skewer and then attaching some sugar to it you create tiny seed crystals. The seed crystals provide starting points for larger crystals to attach to.

Two different processes are at work while the larger rock crystals form. When the water was boiled and the sugar was added until no more could be absorbed a supersaturated solution was created.

A supersaturated solution is unstable, that is, it is it will not stay the same as conditions (such as the temperature of the solution change)—it contains more solute (that is the dissolved sugar) than can stay in a liquid form—so the sugar will come out of solution, forming what's called a precipitate. This process is called precipitation (it is also what happens when clouds condense and the water escapes causing rain).

The other process is called evaporation—as time passes, the water will evaporate slowly from the solution and turn into water vapour. As the water evaporates, the solution becomes more saturated and sugar molecules will continue to come out of the solution and collect on the seed crystals on the string. The rock candy crystals grow molecule by molecule.

If your child loves experiments then why not grab them one of our Chemistry-in-Action kits for endless experiments and fun.


Leave a comment

Please note, comments must be approved before they are published