Science fair ideas: How to make crystals

How to make salt and sugar crystals, with science fair project ideas.

Crystals have always held a particular fascination for people because a high degree of order seemingly emerges out of disorder. And since growing crystals is easy and, in many cases, inexpensive, this activity is one of the all-time classic classroom and science fair experiments.

In nature, the process starts when minerals are dissolved in water and held in solution. As time passes, the moisture from the solution evaporates and the mineral molecules held in solute, with less moisture to hold them, begin to come together and form bonds. As more and more molecules line up, the distinctive crystal shape begins to form. For example, common table salt is made up of two atoms Sodium (Na) and Chlorine (Cl) coming together to form Sodium chloride (NaCl).

When a salt molecule bonds with another salt molecule, they line up neatly like little blocks until the cubic shape of salt emerges.

Salt crystals can be grown very easily and only require a few supplies and a few days to grow.

What you need:

  • A clear glass jar
  • A cup of hot water
  • ½ cup table salt
  • A Popsicle stick or pencil
  • Cotton string
  • A weight for the bottom of the string (large paper clip or a washer)

What to do:

Heat the water until it is very hot and place it in the jar. Then spoon the salt into the water a tablespoon or two at a time. Sprinkle the salt from the spoon slowly and don’t stir it – it should be allowed to dissolve on its own. Let each spoonful dissolve before placing the next spoonful in. As you get closer to using up all the salt, you will notice that a little salt is collecting on the bottom and is not dissolving. When you have reached this point you have reached super solution and are now ready to grow your crystals.

Tie a weight on one end of the string and the other end to the Popsicle stick. (You will need the weight to hang about an inch or so from the bottom of the jar.) Dip the string into the solution a few times and let it dry. Repeat this a couple times more. This allows small seed crystals to form on the string. Your crystals will then grow on these seed crystals.

Now, place the string into the jar and hang it from the rim with the Popsicle stick. A good idea is to cover the jar lightly with a paper towel to keep dust out (this also wicks moisture away and helps the water evaporate more quickly).

Place the jar in a place where it will not be jostled and allow it to sit for a day or two. As the water in the jar begins to evaporate, crystals will start to form on the string. The longer you leave them in the solution, the larger they will grow.

A fun variation on this experiment is to use sugar instead of salt. Mix hot water and sugar until it becomes very syrupy and then follow the same directions as above. Sugar crystals are a bit more sluggish in growth than salt crystals, but their slight prism shape is more striking, not to mention that you can eat them!

In addition, more complicated and impressive crystal growing kits, as well as fine crystals and geodes, can be purchased from online merchants. You may even find that what begins as a classroom experiment or science fair project may turn into a fascinating hobby! Have fun!

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