chemrox
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kid's crystal kit
My helper's daughters are very bright (and beautiful) for their ages; 8 & 11. Both excell at science and we want to encourage their intellectual
development and reward them for recent accomplishments. They've both expressed interest in crystal growing. I was thinking I could get some nice
colors from a pottery supplier. I'd like recommendations from one or more of you inorganic types. The materials should be of relatively lower
toxicity where possible. They should be bright of color and not all in the same symmetry group. It would be nice to have some hexagonal or trigonal
as well as monoclinic.
Thanks,
CRX
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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chemoleo
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1. potassium aluminium sulphate - the probably most popular choice of crystal growers - it can be laced with the potassium chrome sulfate variety to
get purplish colours
2. copper sulphate, see crystal growing thread. I'm a proud producer of several >1kg crystals 
3. NaCl - ok most sites advice against it because it is such a common occurrence, but! it is easy, commonly available, and forms nice cubic crystals.
Non toxic too, and I don't think kids would want to eat a pound of it 
4. potassium phosphates, but they are all clear, so all that's different to 3. is the space group.
5. Ni sulphates...hmmm...toxicity.
6. Ammonium ferric sulphates, oxalates, etc. But again, nothing for the beginner really.
7. Cyanoferrates, +2, +3 - nice vivid colours (yellow, red), nice crystals, and not very toxic as far as I know. Unless you drop strong acid into it.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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crazyboy
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I agree I would think the best crystals for beginners or children would be:
1. Copper sulfate: fast easy brilliant blue crystals.
2. Alum aka aluminum potasium sulphate: easy cool looking crystals
3. Silver nitrate: very fast cool looking.
4. Salt or epsom salt crystals: easy cheap fast non-toxic
this website has lots of info including a section dedicated to safe and easy crystal growing enjoy!
http://www.waynesthisandthat.com/crystals.htm
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bfesser
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How about sodium thiosulfate? Granted it's not colorful, but it makes up for that in low toxicity.
And as for silver nitrate, wouldn't that be a little too toxic (not to mention light sensitive)?
Here's a convenient list:
http://www.sciencecompany.com/sci-exper/crystal_chemchart.ht...
[Edited on 2/5/08 by bfesser]
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chemrox
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Wow-the information you've all given is really great-thanks so much!
The girls are very pretty and will soon receive a lot of attention for their beauty. We want to reward their intellects and encourage them to be
smart.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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12AX7
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Those crystal kits never work. This is even from personal experience, but I even have a cite; unfortunately I can't find it. I'm pretty sure I saw
it somewhere on James Calvert's website.
Tim
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microcosmicus
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In addition to growing crystals, you might want to demonstrate some of the
amazing optical and electric properties of crystals. Here are some crystals
you can grow from common materials at home or easily obtain (say at a rock
shop) which exhibit remarkable properties:
Sodium nitrate and calcium carbonate are birefringent. You might want to
grow a crystal of NaNO3, then cut it into a sheet and polish both sides (sand, then
smooth out with water). Upon looking through this window, you see everything double!
Sucrose and sodium potassium tartarate (Rochelle salt) are
piezoelectric --- if you squeeze them, they generate electricity and, reciprocally, if
you apply an electric field to them, they will change shape. I'm not sure how to make
a nice demo of this for kids, maybe somebody else around here some ideas, the
best I can think of is something like squeezing a crystal in a clamp and maybe getting
it to attract dust or an electrically charged ball or perhaps connecting the ends to
a foil electroscope (if you haven't done so already, build your budding scientists one
of these instruments --- get a copy of Graf's Safe and Simple Electrical Experiments
for more information (I have fond memories of this book from when I grew up --- 20
years later I was teaching E&M class, so it the book is a proven success 
)) To
grow sodium potassium tartarate, you can mix potassium bitartarate (cream of tartar)
with sodium carbonate or sodium bicarbonate . To every 198 parts (by weight) of the
KC4H5O6 add either 116 parts Na2CO3.7H20 or 84 parts NaHCO3 (since it's late,
you might want to double-check my stoichiometry).
Another neat effect is pyroelectricity --- when you heat a polar crystal, it becomes
electrically charged. The classic example is tourmaline --- get a crystal from a
rock shop, heat it and notice the static attraction. Unfortunately, the substances
usually used for pyroelectric effect are not the sort of things you would be growing
with kids; however, since polar crystals are pyroelectric, you should likely be able to
demonstrate this effect with crystals grown at home.
While on this topic, it is worth pointing out that monobasic phosphates are noteworthy
for their electro-optic properties --- their index of refractions varies as one applies
an electric field. However, the only demonstrations I can think of involve high voltages,
lasers, and the like so might be more suitable for when the girls grow up to the age
where they are posting here
On a different subtopic, in addition to growing crystals from solution, maybe grow some
crystals by freezing. In addition to good old ice, you could grow crystals of paraffin
wax or stearic acid (sold in the candlemaking section of craft stores). You might want
to even try some metals with low melting points (my first experience with molten
metal came when I was the same age as the kids in question). You can grow rather
fascinating crystals from bismuth. At a slightly higher melting point, maybe do zinc
and tin. Also, if you take a piece of cast zinc or cast iron and snap it, the edges will
be rough and with a magnifier you can make out the crystals --- it is definitely worth
pointing out to the kids that metals are crystalline substances. Another neat
demonstration with metal crystals is the Czochralski process --- if you dip a rod
into a pot of molten tin and slowly pull it out, you will be rewarded with a long,
thin single crystal of tin. (By the way, Czochralski's discovery is a classic tale of
absent-minded serendipity --- instead of dipping his pen in the inkwell, he reached
for the crucible (!) and noted that there was a crystal stuck to the tip of
his pen.) Also, compare the single crystal with an ordinary (polycrystalline)
piece of tin wire.
To conclude by tying together the two themes, there is ferroelectricity. If
they are crytstallized in the presence of an electric field, many types of
waxes will retain a permanent electric charge. For further discussion on how
to make electrets, what waxes are most suitable, etc. see the old Scientific
American column. Again, because of the high voltages involved, this may
not be suitable for small kids. However, you could make some electrets
and give them to the children to play with --- show how they are electrically
charged on the ends, how they have two poles just like magnets, how
they attract and repel each other, etc.
[Edited on 6-2-2008 by microcosmicus]
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woelen
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Another very nice experiment with crystals is the "melting" of sodium acetate 3-hydrate or sodium thiosulfate 5-hydrate by careful heating.
Let the melt cool down and drop in a single crystal of the solid. Within 10 seconds or so, you see the liquid solidify, with all kinds of crystalline
appearances in it (glittering structures). This effect is very nice to watch. It can even be done on a test tube scale. The kids then can do the
melting themselves by immersing the test tube in a cup of hot water.
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YT2095
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if you go to a gardening suppliers you can buy a several kilo bag of Magnesium sulphate for next to nothing, these make Very large and clear crystals.
have a look around and see if you can get some "Water glass" sodium silicate, this stuff is also non toxic but allows you to make chemical gardens
take a look here: http://chemistry.about.com/od/growingcrystals/a/aa060704a.ht...
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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not_important
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Sodium carbonate easily grows large rhombic crystals on allowing a warm solution to cool. The crystals lose water if removed from the liquid, slowing
crumbling away as a white powder.
Nickel and cobalt ammonium sulfates both crystalise decently.
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12AX7
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Concerning zinc, notice that cents of various countries, at various times, are (or have been) copper-plated zinc, with a melted composition of around
2.5% copper. This is near the eutectic (2.7%, IIRC), so although you get apparently crystalline structures (columns of perhaps hexagonal shape, but
may be hexagonal by statistics only), they are round, globular and coarse, probably covered in a "druse" of actually hexagonal zinc crystals. Coinage
is a tempting source of zinc, but not effective.
A pure sample of zinc will form better crystals. A strip or bar of zinc can also be bent, revealing "tin cry", where slippage planes in the crystal
lattice give way at supersonic speed, creating a minute shockwave inside the material -- and a distinctive sound. A strip of rolled zinc may not
produce good results; it can be annealed by heating just below the melting point, causing the crystalline structure to consolidate (crystals may be
visible after just this step!).
Tin cry is, in and of itself, an interesting phenomenon. I have observed it in annealed zinc and iron, and others have observed it in tin, indium and
others. (I wonder if frozen Hg "cries" below some temperature?)
Tim
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Fleaker
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Frozen Hg is very brittle in my experience. It is also remarkable easy to handle with your bare hands when cool, and takes quite a while to warm up to
a liquid. IIRC, it's specific heat explains this. I don't think it would bend, most likely shatter.
I would show them the formation of bismuth crystals. Very pretty crystals of good size can be made, and it will probably seem magical to them to see
something as dull as bismuth metal make such interesting crystals. It is one that I wouldn't let them do by themselves since molten bismuth is a bit
warm for kids to play with, but surely something that they should see.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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UnintentionalChaos
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Sodium sulfate makes wonderful, big crystals if you cool a solution slowly without disturbing it. Sorry, I don't have pictures of them in their usual
form. They look remarkably like big crystals of lead acetate trihydrate (which I've also made) but without the toxicity. It also tends to crystallize
in different forms so every time is a surprise. You might get perfect, well defined crystals or tightly packed acicular crystals depending on
concentration. I once got this wonderful, bizarre crystal...huge and covered in tiny crystals, but each one well defined in the bottom of a beaker.
I've attached a picture.
Also adding my vote for copper sulfate since it is easy and makes great crystals. I've gotten beautiful crystals of calcium chloride to form in a
syrupy solution that I was attempting to recrystallize when I left it in the cold garage with dry air for a week or so....I wouldn't try to repeat it
unless you're crazy.
[Edited on 2-8-08 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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12AX7
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An excellent crystal formation there!
Drying an NaBrO3 solution, I have also had clumps of that type of crystal. I've seen it with a number of other salts too (NH4HSO4 is one I think, but
I'm not sure that's what it was). The "crystals" share planes, but they are quite friable, aren't they? Weird!
Hah, there's a tub of CaCl2 dessicant stuff (I can't remember the brand name) in the bathroom closet. There are crystals in the tub below the tray
the crystals sit in. Yeah, we have *dry* winters!
Sodium sulfate can grow impressive crystals, but they are short lived; they dehydrate incredibly easily. I've grown substantial magnesium sulfate
(heptahydrate) crystals, though they too contain an excess of water and decay in air, probably to the hexahydrate, or less.
In my warm ventilated cabinet, I ever so slowly crystallized MgCl2 hydrate. Probably with a notable KMgCl3 / K2MgCl4 impurity, coming from KCl +
MgSO4 metathesis. The crystals are more or less cubic, I think. Not really well formed, as you might guess from the extremely concentrated sort of
solution they formed in. But I'll tell you this: they're in a ziplock bag on my shelf and hardly clump at all. I got them pretty dry, apparently!
Tim
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kilowatt
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Ammonium nitrate makes long needle-like crystals, not very colorful but interesting nonetheless. Nickel salts are among the prettiest imo, despite
their toxicity. I don't see where it's a problem as long as the kids know not to eat them, and proper hygiene handling the crystals or solutions.
One interesting demonstration of crystal structure that would be excellent to introduce them to is the transformation of pure tin from metallic to
nonmetallic gray tin by putting it in the freezer. You could then melt it down again to metallic tin. Similarly with yellow and red sulfur
allotropes.
The mind cannot decide the truth; it can only find the truth.
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UnintentionalChaos
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Yeah, it's a shame sodium sulfate crystals are so short lived....but they are very easy to make and rather impressive. As kilowatt said, ammonium
nitrate does make well formed needles but I've always found it to be a pain because of its very steep solubility curve. I've had very nice results
with KNO3 though. I was recrystallizing some stump remover and the solution went from hot to almost room temperature and I filtered off a crop of
small crystals. Then I stuck it out in the cold garage and it slowly cooled down overnight yielding surprisingly thick white needles...growing down
from the surface of the solution. Some hit the bottom and acted as supports for the whole formation I suppose.
As far as organics go, I've gotten interesting results from vanillin. It seems very capable of forming supersaturated solutions and when agitated, you
can see starbursts of extremely fine needle like crystals expand from the nucleation sites. If you seed it or your beaker has some decent nucleation
sites, slow cooling will yield thick pale yellow needles.
Woelen has that beautiful experiment with recrystallizing lead iodide, but you don't want anything toxic...
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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12AX7
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The formation of potassium chlorate is quite interesting. Mix not too strong solutions of potassium chloride and sodium chlorate, and before your
eyes, shiny, iridescent flakes of potassium chlorate crystallize out of solution. The formation is much slower than, say, KClO4, which tends to give
a flocculant precipitate. The slow rate of formation makes for some nicely dimensioned crystals to watch. They are flat, so they float slowly to the
bottom as well.
Tim
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YT2095
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Agreed, and best watched in a room with sunshine on the beaker, beat`s Any snow-globe
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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chemrox
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gratitude
I'm overwhelmed! Thank you all so much! I have demonstration experiments that we can show them in the lab (high voltage, etc.), participation
experiments we can do with them and some really funs stuff they can do on their own and show us. Wow!
One clarification- I'm not worried about the ingestion pathway, not at all. Dermal contact toxicity or inhalation of friable materials or vapors are
the things I had in mind. If we tell them to use gloves and wash their hands before eating they will whether we're present or not. It's up to their
father but I think I'm expressing his view as well. In any case he will look to me for the safety concerns.
I would like to make a foil electroscope to demonstrate some of the electrical properties. I don't have a mineralogical microscope, alas, but some
of you have given me ways to show optical properties without one and that is too damn cool! I don't see a problem with crystals disintergrating when
we can keep them from doing so by keeping them humidified and observe them disintegrating as dehydration phenomenon. Maybe we can weigh them first
and measure the water loss when they fall apart.
In a few months we'll be considering Science Fair projects too so if we have a tie-in so much the better.
Thanks again, really!
CRX
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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YT2095
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if you really did want to keep a particularly nice specimen you could always buy some clear varnish or spray shellac
as for the electroscope, see if you can get hold of the plastic anti-static bags that HDDs come in, the clear silvery sort, this cut into strips makes
Excellent leaves for an electroscope, noticeably out performing regular tinfoil 
[Edited on 9-2-2008 by YT2095]
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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not_important
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Better way to keep sodium sulfate or carbonate crystals is in a tighly sealed jar with a small amount of the starting material and water at the
bottom, with a stand to keep the sample from touching it.
Make a saturated solution of the starting material, put enough in the sample jar to cover the bottom a few mm deep, then add enough solid but hydrated
starting material to cover the liquid.
Alternatively you could keep the liquid + solid in a smaller, vented container within the sample jar.
The mix of saturated solution and hydrated crystals keep the air at the proper humidity so as not to dry out the sample crystal.
A varnish coating usually has enough porosity to let the crystal lose water slowly. Actually encapsulating the sample in plastic resin can work, if
you avoid leaving a leakage plain or path.
--------------------
For substances with really steep temperature-solubility curves, try using a thermos bottle. Use a waterbath to heat the starting solution, fill the
thermos with water from the bath a let it sit for several minutes to preheat the thermos. Then drain, rinse the thermos with a bit of the hot solution
to be crystalised, and fill with the solution. Hang a seed crystal or weighted bare wire or thread from the lid. Close it up, let sit for some
hours; a little experimentation gives you the proper amount of time.
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