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Sugar crystal rock candy

You will need:

  • Sugar 300g
  • Saucepan or kettle with 500mL of water (adult help!)
  • Wooden kebab stick or chopstick
  • 2 clothes pegs
  • A glass
  • A metal spoon
  • A place to leave the experiment setup away from ants
  • Optional: food colouring

    Copyright
Rock candy crystals
Rock candy crystals

Instructions


The experiment is similar to growing salt crystals, except the supersaturated sugar solution is hot, so have an adult handy.
 
  1. With adult help, carefully heat the water in a saucepan. You may want to add some food colouring as an optional extra too!
     
  2. Stir in the sugar slowly, stirring constantly whilst the sugar dissolves. Keep adding sugar until you cannot dissolve the sugar crystals anymore. At this point just add a tiny bit more water and dissolve the leftover crystals as well.
     
  3. Pour the saturated sugar solution carefully into a glass.
     
  4. Use two clothes pegs to suspend the wooden kebab stick or chopstick in the sugar solution without the stick touching the sides of the glass. Place the glass in space where ants cannot get at it (you might want to cover the experiment with a cloth).

    Rock candy setup
    Using pegs to suspend a chopstick on the saturated sugar solution
     
  5. You may want to setup several experiments to see if the crystal formation differs with different amounts of sugar in the water. It's all about variable testing!

    Multiple rock candy experiments
    Multiple rock candy experiments 
     
  6. Observe the experiment over several days, taking note of when crystals start to form.

    Rock candy growing
    Rock candy beginning to grow on the chopstick
     
  7. Run the experiment until you have grown the large sugar crystals along the stick (without the crystals touching the side of the glass). 

    rock candy crystals
    Rock candy crystals 

    Eating rock candy
    Eating rock candy!

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Why Does This Happen?

You made a supersaturated solution of sugar and water! The sugar crystals could only stay dissolved whilst the water was hot. Cooling the solution down made it super-saturated, which is unstable. As water cooled down less of the sugar crystals could remain in the water and so they began to settle out onto the kebab stick, which effectively acted as a seeding crystal. More and more of the sugar continued to settle out of the solution onto the kebab stick and so your crystals continued to grow!

The longer it takes to form a crystal, the larger the crystal will be.
This works whether you are talking about crystal growing kits, making liquid nitrogen ice-cream or gemstones!
Check out the link on crystals formed by volcanoes; Indianapolis Childrens Museum

Similar experiment: Borax crystal snowflakes

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