Crystal growing:

Salt (sodium chloride or table salt) produces big crystals and you can colour them to make them easier to see.
Try phenyl salicylate also known as Salol. This solid melts at 41 to 43 degrees C so if some is placed in a test tube and then placed in hot water it becomes a liquid. Students can then drip some onto a slide and the crystals form almost instantly. It is available from Crown Scientific and Perth Scientific Equipment.
Also try ammonium chloride, magnesium sulfate and sodium thiosulphate.
Specific experiments:
Conical flask 150 ml
25gm copper sulfate
50mL water
Few drops of concentrated sulfuric acid
1.Supply 2 flasks containing 25 grams of copper sulphate and 50 mL of water.
2. Heat and dissolve the copper sulphate, forming a saturated solution.
3. Cool one flask quickly by placing in a bucket of ice.
4. Cool the other slowly by wrapping the flask in cotton wool, then alfoil.
5. Leave both flasks overnight.
6. Examine the crystal formations.

The formation of crystals can be demonstrated on an overhead projector or with a video-flex.
Copper sulfate, potassium nitrate and alum (aluminium potassium sulfate) produce the best crystals.
Saturated solution
Glass petri dish
Hot plate or Bunsen burner
Jar of the solid chemical
Boil 50 mls of the saturated solution.(For saturated solutions,look up solubility table. At 20 degrees Celsius: copper sulfate 20.5 gm per 100ml water; potassium nitrate 31.6gm per 100ml Alum 6.3 g per 100ml)
Add more solid until no more dissolves.
While still hot, pour a thin layer into a petri dish.
View on an OHP or through a video flex.
Copper sulfate:
Crystals start to form within 10 minutes. If left overnight, the whole dish is covered in the familiar shaped crystals.
Potassium nitrate:
In test tube, does not form immediately. Overnight, structures of tall crystals form.
On petri dish, crystals start to form after 5 minutes. Particularly spectacular if left overnight.
Alum which is Aluminium potassium sulfate:
Petri dish- forms small crystals within a few minutes. These grow fairly rapidly into beautiful shapes.
Test tube-not very interesting.
Potassium chlorate:
Produces the best crystals in a test tube, the crystals falling out of solution as you watch.
Sodium nitrate:
Crystals are not very interesting, with a fuzzy mass forming in the petri dish.

If you want to investigate other ideas, type in crystal growing or crystal recipes in a web search.

Leave a Reply

Your email address will not be published. Required fields are marked *