Super Saturated Sugar Strings

sugarstring2

Making your own rock candy isn’t just a tasty treat, it is a great way for kids to learn about solutions and the changing properties of substances.  This is surely everybody’s favourite science fair project!

Remember however, that some patience is called for so make sure you give yourself plenty of time to complete this – we’d say two weeks to be on the safe side.  Speaking of which, this activity absolutely MUST BE SUPERVISED BY ADULTS.  Boiling sugar solutions can be very dangerous!

If you want to have a go at making rock candy here is our foolproof method!

You will need the following in order to carry out this experiment:

  • One cup of water (This is the solvent)
  • Three cups of  granulated sugar (This is the solute)
  • A little extra sugar and water to prepare your string.
  • A large saucepan
  • A glass jar
  • A pencil, chopstick or similar
  • Rough, cotton string.
  • Food dye and flavouring (optional)
  • Toothbrush (not strictly part of the experiment but advisable if you are going to eat your rock candy!)

What to do:

  • Start by preparing your string a few hours in advance. Mix just a little sugar and water together and dip the last few centimetres of your string in this and then straighten it out and hang it somewhere to dry.  A saucer to catch any drips will keep surfaces clean and ‘ick’ free!
  • ADULT PARTICIPATION ESSENTIAL HERE! Place your water and sugar in the pan together.  Heat the solution and gradually bring to the boil.  Stir the solution all the time.  Allow it to boil only briefly and then take it off the heat.
  • At this stage you can add food dyes and flavourings if you wish.
  • Pour the solution into the glass jar.  (We then put ours in the fridge for a few minutes to aid rapid cooling.)
  • Attach your string to your chopstick or pencil so that the end you prepared is dangling down and then balance the pencil across the top of the jar with the string dangling down.
  • Place your jar somewhere where it will not get disturbed.  Watch and wait.  Be patient!

sugarstring

It took ten days for our rock candy to reach this stage.  You can keep on growing your crystals for much longer if you wish, but our Little Sparks could wait no longer to get their teeth into their sugar strings!

What Happened Here?

Your solution contained three times the volume of sugar to water.  Under normal circumstances the water would not be able to absorb this much sugar.  You can do a further experiment here.  Fill a jar with a small amount of water (solvent) and add sugar (solute) to it at the rate of one teaspoon at a time.  Stir the solution until the sugar dissolves and you can no longer see it.  Keep on adding and stirring until you reach the point where the sugar will not dissolve and you can still see the sugar crystals in the water. At this point the solvent has become saturated and cannot absorb any more solvent.  However when you heat the solution, as you did when making rock candy, all of the sugar dissolves and is absorbed.  This is known as a super saturated solution.

A good example of a super saturated solution is honey. Super saturated solutions are unstable and as is the case with your rock candy the sugar cannot remain in solution and so starts to recrystallize.  Honey often crystallizes when it is stored too cold.The new crystals will attach themselves to any surface, but the prepared surface of your rough string is ideal.  Study your crystals carefully.  Observe their shape using a magnifying lens.

What was learned?

Concept: solutions, solvents and solutes.

Concept: saturation and super saturation.

Scientific enquiry: observation, use knowledge of concepts to explain changes in materials.

{ 2 comments… read them below or add one }

Kristin @ Preschool Universe June 28, 2011 at 4:16 am

I was thinking about trying rock candy just the other day. Glad I found this – you seem to know your stuff. Great tutorial.
Kristin @ Preschool Universe recently posted..All Kinds of Free Montessori Resources for PreschoolMy ComLuv Profile

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Mandy June 28, 2011 at 7:42 am

Thanks Kristin, glad you found us too! Enjoy the rock candy!

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