UNIVERSITY AT BUFFALO CHEMIST JASON BENEDICT: This is the second video in a two-part series on how to grow a large, single
crystal. In the first video, we showed you how to grow a seed crystal. The second
video is going to show you how to turn this seed crystal into a large, single [Benedict in a chemistry lab.]
crystal. And so what are we looking for in a large single crystal? Well we want
large, flat faces, sharp edges. And we'd like the crystal to be as [Benedict holds up a crystal the size of a ping pong ball.]
see-through as possible. And we also want it to be a single
crystal — just one crystal. And that's what we have here. To turn our seed crystal
into a large, single crystal, we need to place our seed crystal in an alum
solution. As the water evaporates the alum needs to come out of solution, and
if our seed crystal is present, the alum will stick on to that seed and cause the
seed to grow. Now there are a lot of different ways to put a seed crystal in [Benedict in a lab.]
a solution of alum. I like to use fishing line. Here we have 0.3 millimeter fishing
line. You can pick this up at any sporting goods store or craft store. Now, [Benedict holds spool of fishing line.]
you may have seen in some of my other videos that I tried to glue the fishing
line to a crystal, and it didn't really work out so well. So my preferred method
is tying, and the way that I do this is I actually get my string, and I tie a
slipknot. If you're not sure what a slipknot is, search the web and find out. [Benedict holds a fishing line about 10 inches long, with a looped slipknot at one end.]
But, basically, it's a nice little loop that's going to grab on to whatever you
put in the middle. So we have our we have our slipknot, and we have our seed
crystal. We can just sort of fish our slipknot onto the seed crystal. There we [Benedict puts knotted fishing wire around seed crystal.]
are, come on you. And there we have it. We have [Benedict tightens looped fishing wire around crystal by tugging on the wire.]
our crystal securely fastened to the string. We have this little extra
piece of string. We can go ahead and grab a pair of scissors and just carefully
snip that away. And now we have a crystal that's ready to be submerged in [Scissors snipping excess fishing wire near slip knot loop. You should not snip off the long end of wire.]
a saturated solution of alum. So it's actually a good idea to prepare a few
seed crystals, because we'll be taking these seed crystals and putting them [Benedict holds several seed crystals tied to fishing line.]
into a solution of alum, and a lot can go wrong. And so you may need a
backup seed crystal, and I'll get more into the details a little bit later.
You may remember from our last video that we harvested seed crystals from our
large, flat dish. We don't want to put the seed crystals back in here because, as you see, [Benedict gesture toward large, flat dish on lab counter.]
there's lots of other crystals around. We want to heat this solution up to get all [Overhead view of dish showing small clear crystals at bottom.]
of these crystals to dissolve. And so to do that, in this case we're going to want
to transfer it to a container that is suitable for heating. So we just
carefully pour this in, and this is again where a squirt bottle can come in handy [Benedict pours solution from flat dish into a glass beaker.]
to help rinse some of these little crystals in there. Now I'm not going to [Benedict uses squirt bottle to spray water on bottom of dish to loosen small crystals, which are also poured into the beaker.]
spend 20 minutes getting all those little crystals out, but I recommend that
you do. Now, we've added a little bit more water back in here through the process
of cleaning our dish. But how much water do we want? The short
answer is, we definitely want less water than that. This blue line indicated the [Benedict points to small blue line on side of beaker.]
amount of water that we used to initially grow the seed crystal. And the idea is, if
we put that much water back in here, it's just gonna redissolve our seed crystal. So
we want a little bit less water than that, but exactly how much? That's [Benedict in the lab.]
something you'll have to experiment. Too much water, and the seed crystal's going
to dissolve. If there was too little water, the alum is going to want to
crystallize out incredibly rapidly and could potentially destroy the seed
crystal. So you want just a little bit less water than you started with for
your seed. So we'll go ahead and take our container put it on the hot plate and
let this start heating. If you have a lot of solid material down there, you might
consider stirring this, but in our case, there's not much left, so
we'll be fine without a stir bar. TEXT ON SCREEN: Heat the solution to about 45 to 55 degrees Celsius. When all of the alum has dissolved, let the solution cool.
We want to get an ideal crystal shape. And the reason we suspend the crystal in
the solution is because if a crystal grows against the bottom
of a dish or against a surface, you're not allowing the crystal to grow
equally in all directions, and that's what can give rise to some of the
irregularities here. These crystals likely grew on the bottom of the dish. [Five odd-shaped crystals, including flat ones.]
Again, when the crystal grows against a surface, the crystal can't really grow in
that direction, and so you wind up with generally very odd-shaped crystals. When
the crystal is suspended in the middle of the solution, all of the directions of
the crystal have the ability to grow, and very often that will lead to
crystals with the ideal crystal shape. So one of the things that can go wrong is [Close-up of large, single crystal.]
adding your seed crystal to a warm alum solution. Now, if the solution of alum is [Benedict in the lab.]
warm, it's almost certainly going to dissolve your seed crystal. And that's [Footage of small crystal shrinking in a warm solution.]
what you'll see here. So here is our cooled alum solution, to which we want to
add our seed crystal. Now, how do we suspend the seed crystal in the alum solution? [Benedict with glass beaker filled with clear solution.]
I like to use some sort of an irregularly shaped long thin object. If you use [Benedict holds a plastic knife.]
something round like a pen or a glass rod, it can roll around. Using something
flat helps hold this in place. And so what we'll do is we just attach our seed
crystal to this. Whatever object you want to use, take a little piece of tape and
tape it in place. Cut off the excess string, and [Benedict attaches fishing line to plastic knife. Seed crystal hangs from bottom of the line.]
here we go. We're ready to submerge our crystal. Now here we can see it's [Benedict places seed crystal in beaker holding solution. Plastic knife goes across top of beaker.]
hitting the bottom. We don't want the crystal on the bottom of the dish. We [Seed crystal hanging off the fishing line sits on the bottom of the beaker.]
want to raise it up a little bit, and so that's a nice thing about this cutesy
little trick. We can just rotate this knife a couple turns. It lifts the
crystal up, and now the crystal is suspended midway in the solution. And [Seed crystal dangles in beaker holding alum solution.]
this is exactly what we're looking for. There's no other crystals around. So now,
any alum that wants to crystallize out of solution is going to [Benedict in the lab.]
be preferentially attracted to the seed, and the seed is going to grow. Crystals
like to grow in an area where they're not going to be disturbed. Ideally, this
will be a dark cabinet. It'll be dark, there's no light. It's going to be free
of air currents. And one thing you might consider doing is actually setting this
on a nice piece of styrofoam to help not only thermally insulate it, but also to [Benedict gestures to beaker holding seed crystal and alum solution.]
potentially free it from vibrations that could cause unwanted crystallization. So
we'll go ahead and put this in a dark cabinet. So here we have an example of a [Benedict lifts beaker up.]
crystal that I've been growing for about a week or so. It started out exactly like
this — a single crystal and a beaker without any other crystallites — but [Two crystals growing in beakers. One is in a clear solution. The other is in a solution with small crystals at the bottom.]
here, a week later we can see that not only has our seed crystal grown, but now
we have a bunch of other crystallites all around the beaker. The trouble is, [Tiny crystals at the bottom of the beaker.]
these extra little crystallites are alum crystals that are growing, and
they're going to take away from the maximum size that your seed crystal can [Benedict in the lab.]
achieve. So how do we get rid of these parasitic little crystals? What we're
going to want to do is pull our crystal out of solution, reheat the solution, and
let it cool, and then put our crystal back in. The first step is to pull the
crystal out of solution, and like I mentioned last time, you're going to want
to squirt this off to prevent any possible little crusties from forming on [Benedict lifts the crystal out of the beaker and sprays it with water from a squirt bottle.]
the surface of the crystal. And we'll just go ahead and set this to the side. [Benedict places crystal on paper towel.]
So we have our solution. We're going to put it on a hot plate. [Benedict holds glass beaker.]
And this is where we're gonna want to pay attention to our blue line again. So
once again, the amount of water is critical. This blue line represents the
amount of water that was present when I first introduced the seed crystal. We're [Benedict points to small blue line on the side of the beaker.]
going to want to add back in some water to this solution, but not quite to the
blue line. The reason you want to add a little bit of water back into this
solution is we have a lot of extra alum at the bottom. If we didn't add any more
water, when this solution cooled back down, all of this alum would want [Benedict in the lab.]
to rapidly come out of solution, and it would it be like a snow globe. There
would be alum powder everywhere, and it could really jeopardize the appearance
of our seed crystal. Now, we're just going to heat this up until all of these
crystals dissolve. We're going to let this solution cool back down, and once the
solution is returned to room temperature, will reintroduce our seed crystal.
Okay. We have our cooled solution, and again, the liquid is a little bit lower than
our original blue line. And so we can go ahead and add back in our nice alum [Benedict points to water level, which is lower than the blue line on the side of the beaker.]
crystal. Now at this point I'm going to take my trusty marker and add a new blue
line. The second blue line is a convenient reference point, because as we [Benedict draws a small blue line to mark the water level in the beaker.]
let this crystal sit, water is going to evaporate, and at some point we're going
to get more of those little parasitic crystals that we need to get rid of:
We're going to have to remove the crystal, reheat the solution, add back in
a bit more water. And again, we'll know how much water to add because of our
second little blue line. So now we're going to take our crystal and put it back [Crystal hanging in beaker filled with solution.]
in our dark cabinet and let it grow until we start to see more of those
parasitic crystals, and we'll have to go through another round of removing the
crystal and heating. This is something that you may have to do three, [Benedict in the lab.]
four or five times. You basically are going to have to do this every time you
see a lot of little extra crystals growing
in your beaker. But every time you do this, there's a chance that something can
get messed up, and you'll destroy your single crystal. So you want to do it as
few times as possible. But inevitably, you're going to have to do this. But for
now, into the dark cabinet it goes. Once you have your large crystal going and [Benedict lifts beaker holding single crystal.]
you've been through maybe one or two cycles of removing and
heating to get rid of parasitic crystals, it's probably a good idea to take any of
the leftover seed crystals that you have and toss them in there when you do [Benedict holds up a seed crystal.]
another heating cycle, so that you make sure you have all 100 grams of alum at
play in the beaker. So that concludes our two-part series on how to grow a large, [Large crystal dangling in beaker.]
single crystal. In a few weeks, with any luck, this crystal will turn into a [Benedict in the lab.]
crystal worthy of winning the U.S. Crystal Growing Competition. Thanks for watching. Good luck with the crystal growth!
[Lighthearted music plays.] [University at Buffalo logo on blue background.]