Australia's Science Forum

This is our first year using Nelson Science for Australian Curriculum. The unit "Rocks" has a practical to investigate Crystal formation which involves dropping "Salol or Phenyl salicylate" onto either a heated or cooled microscope slide, then observe the differences in the crystals formed.

I have not come across this prac before and I don't have any phenyl salicylate , I can order but it probably won't be here by the time teachers want to do the prac.

Has anyone done this before, how well does it work and is there a substitute for the phenyl salicylate.

Thanks!

We did this years ago. Dropped a little salol onto a slide and passed it through a flame until the crystals melted, then watched the crystals form under a microscope. The slides were stored for future use. The teachers loved it then, but its fallen out of use recently.

Hi maybe this can help you,

Crystals under the microscope:
You need to have the microscope on the lowest magnification.
Make a solution by adding about one spatula of iodine crystals to about 50 mL of methylated spirits. Stir to dissolve- it gives a dark reddish black solution. It is toxic.
Put a few mL of the solution into a small beaker for each group. Each group has a plastic eye dropper and a microscope slide.
Students add one or two drops of the solution to the slide under the microscope and observe. Within 30 seconds or so the crystals start growing before their very eyes….it is quite stunning. After the metho evaporates the crystals themselves disappear because the iodine vaporises quite readily.
They can repeat this many times so each student in the group can check it out.
Remember they should not readjust the focus of the microscope…

regards Superbug

We use a little salicylic acid in metho. You can add some food colour also.

We place a transparent sheet (plastic sheet) on an overhead projector. Place some drops on the sheet and the metho evaporates with the heat from the projector. Class can see on screen the formation of crystals.

I have just been asked for this prac for a year 8 class. Interesting because CSIS has classed it as for use with yrs11-12. Obviously the salicylic acid would be a safer alternative. The prac method that my teacher gave me says to heat the phenyl salicylate with a Bunsen which is interesting considering its flammable.

http://www.dynamicearth.co.uk/media/124 ... ystals.pdf

I feel very torn as the teacher is my HOD and I really struggle with telling her what I think.
What do you think? Is it safe to do??

If its yr 8 I would talk to teacher. We always use safer (or at least recommended) chemicals. If anything goes wrong you would feel terrible.
Yr 10 is almost there, but nit yr8.
I would be very skeptical even using the iodine crystals, as it is also yr11-12chemical.
Good luck

Just been doing some research and we can either melt the phenyl salicylate with boiling water in a test or on directly on the microscope slide on a hot plate.
I will suggest this to her. Just makes me cross because she's the HOD its her job to do the research and know about these things not me!!!

Just as a "by the way"...could you place those watch glasses on a hotplate instead? Presuming you were going to do it with Salol?

Thanks Smiley. we will do one of those modifications to the prac.

Lorrae

Just another BTW...What's wrong with good old Potash Alum in test-tubes?

We do an experiment where kids make a solution of Potash, pour it into 3 large test tubes, which are then placed into disposable coffee cups - the corrugated cardboard type. One is packed with ice, one with cotton wool, and one left in the air. The tubes cool at different rates, and different sized crystals form. Easy peasy, and the potash is largely recoverable afterwards.

I am with you, Smiley.
We do very similar prac. With new national curriculum, there are a lot of new pracs, but some totally unsuitable for yr 7-8.
Example Iodine with alcohol.
What's wrong with oldies but goodies

Yeh Smiley I agree. The HOD!!! I can't explain. Nothing old is good enough. It has to be wizz bang and amazing! everything off the internet UK pracs US pracs. When I questioned the use of a 11-12 chemical the comment was that's for public (NSW Dept ) schools only. Lack of science practical experience doesn't help either. Trying to do compaction so yr8 and yr9 work etc etc etc!!! Ad nauseum