How to Grow a Large Single Crystal Part 1 Growing a Seed Crystal

UNIVERSITY AT BUFFALO CHEMIST JASON BENEDICT: Hi! This is part one of a two-part video series on how to grow a large single crystal. If you want to grow a large single crystal, the first thing you're going to need to do is grow a nice seed crystal, and we're going to show you how [Benedict in a chemistry lab.] to do that coming up next. What I'm showing today is basically the growth that occurs through slow evaporation. We're trying to keep a constant temperature, and as the water evaporates, the crystals are going to nucleate and grow. And this is where the experimentation comes into play, because the rate at which the water evaporates is all going to depend on the local conditions: the humidity in your room, the temperature of your room, and so on. So what will we need to grow our seed crystal? Well, first we need the crystallization material. If you're involved in the U.S. Crystal Growing Competition, we're using aluminum potassium sulfate dodecahydrate. This comes as a white crystalline powder, and you'll see we have 100 grams of it right [Benedict holds up jar of chemical.] here. What we're going to do is basically just dissolve this in water, [Small plastic dish with white powder in it.] and once we have that solution, we're just going to let it stand. This is actually the nice part about crystal growing, is it's mainly a game of sit and wait. We're going to need to heat up the solution in order to dissolve the alum, and so for that we have a Pyrex glass beaker. You're going to want to make sure you use a some sort of a container that's capable of being heated. If you [Benedict gestures toward glass beaker.] heat the wrong type of container, the container could crack. You could run into all sorts of problems. So here's our container, and we have here a hot plate. Okay. If you're doing this at home you may be working from a stove. It's [Benedict points to beaker on hot plate.] certainly okay to work in pans and metals. The nice thing about working in in glassware is that you'll be able to see and mark the level of water that you'll be using. Okay. So we have we have our beaker in this case we have a stir plate. We have a magnetic stir bar, and we'll go ahead and add that right now. One thing I would like to say before you get started here is make sure you're wearing proper protective equipment. Now alum is a fairly benign substance, so gloves are probably gonna not really be necessary, but certainly you should wear eye protection because of the possibility of splashing in your [Benedict points to protective glasses he is wearing.] face, or any other kinds of potential risks. So we have our stir bar. We'll go ahead and we'll add 100 grams of alum, and now what [Benedict pours white powder from dish into beaker.] we're gonna do is add water. Now, what type of water to use? You could go to your faucet and use tap water. However, tap water contains a lot of minerals and ions and things that can potentially interfere with the crystal solutions. For folks at home, you can go to the store and pick up a bottle of distilled water. Use distilled water not drinking water. Again, drinking [Benedict holds a jug of distilled water.] water is going to have minerals and ions and things like that. So like I said, we're gonna fill this up to 800 milliliters. Now that doesn't necessarily mean there's 800 milliliters of water, but the final volume of our solution will be 800 milliliters, and we're right at around 800 now. This is the [Benedict pours water into beaker holding white powder.] thing: It doesn't have to be exactly 800. In fact, you're welcome to experiment. This is the impact that the amount of water will have: The more water, basically, the longer it's going to take to get crystals, and if you really don't use enough water, you're going to grow crystals very rapidly and very quickly, and that's going to be bad in the case of growing a large crystal. So what we'll do now is we'll turn on the heat and we'll start this thing stirring [Benedict turns on hot plate.] What's important here is just that you're stirring the solution. So if you're at home, you can use a spoon. I would generally use a nonreactive material. I probably wouldn't use a wooden spoon: It can soak up the salt. So it's probably stay away from wood. But any kind of plastic or metal should be just fine, and you just want to stir this from time to time and again. What we're looking for is all of the solid material to dissolve. So again, I'll be back in just a minute with the solution. TEXT ON SCREEN: Note: You do not need to boil the solution. The powder should dissolve at about 45 to 55 degrees Celcius. [Lighthearted usic plays as powder dissolves into water in beaker.] BENEDICT: Here we are a few minutes later. As you can see, all the alum has dissolved. We have a nice clear solution. So you can go ahead and turn off the heat. So what happens next? Well, this is the part where we want to begin our crystal growth. Now, you can let the crystals grow in this beaker. You can just set the beaker in a [Benedict taps beaker.] dark cabinet. Crystals like to grow best somewhere where they're not going to be disturbed, right? So a dark cabinet is perfect: no light, no vibrations, no big temperature changes. But personally, I like to give the crystals a bit more area to spread out. What you're going to see is the crystals are probably going to start growing on the bottom of the beaker. By using a wide flat dish, the [Benedict taps a wide, flat transparent dish.] crystals will generally be more spread out, and this gives them the chance to grow larger without sort of bumping into each other. We can just transfer our solution. There's a little bit of steam, we can see it's a little bit warm here. [Benedict pours solution from beaker into wide flat dish.] Now if this is a competition, you have a little bit of solution still in there, so it's a good idea to maybe spray it out with a little bit of extra water. No big [Benedict grabs squirt bottle and sprays inside of beaker.] deal. The only thing adding more water will do is slow down how quickly the crystals grow. So, obviously it's a competition. It's limited time. You don't want to be too slow, but adding a little bit of extra water here and there isn't going to hurt anything. And so what we'll do is place this dish again, in a a dark cabinet really is ideal, and begin [Benedict talks about the flat dish holding the crystal solution.] the waiting game. I want to quickly run through something you might experience when dissolving your alum in solution.If you notice that you've heated your water up to about 50 degrees and it still looks a little bit cloudy, you want to [Benedict taps a beaker holding a cloudy white solution.] look inside. If you don't see any solids, this cloudiness is actually a consequence of some impurities that might be found in the alum. Boiling will not get rid of this cloudiness. If there are no more solids, the alum has dissolved, and you're done. Don't heat it any more. What we found is that these impurities that cause this cloudiness will actually settle to the bottom if you wait about 24 hours. Here's our solution after about 24 hours, all the sediment has settled to the bottom, and now we can just decant [Benedict shows beaker with clear water and white sediment at bottom.] off the top layer into our crystallization dish. Now you want to do this carefully, because this sediment at the bottom will re-disburse if you agitate the beaker too much. So here we go. And we're gonna stop right about [Benedict pours water into large flat dish, leaving white gunk at bottom of beaker.] there. Okay, so here's our white cloudy precipitate, and now we have a beautiful nice clear solution of alum, and we're gonna be ready to grow some seed crystals. Alright. So here we have a solution that has been sitting actually for a few days. This is the magic of cinematography. We can see our solution now has crystals. Well why are these crystals in here? Well the reason they're here is the solution basically became supersaturated. This amount of water could no longer hold 100 grams of alum. Some of that alum has to come out of solution and it crystallizes out. These will be the seed crystals that [View of crystals at bottom of a wide flat dish.] we'll use for the next part of the experiment. Now we're going to harvest the seed crystals. We have this camera set up right here so that you can get an in-depth view of what's going on. You want to harvest the seed crystals when the crystals are as big as they can be without bumping into each other. And so how do we do this? Well, you're going to want to grab a pair of tweezers and perhaps a little squirt bottle. Not totally necessary, but it's [Benedict holds up tweezers and squirt bottle.] helpful because, remember, this solution here is a saturated salt solution, and so if you pull these things out and just set them down, the solution will dry and put crusties on the crystal. So what we're [Overhead view of crystals in large flat dish.] gonna do is go in here and find a nice little crystal. There we go. And give it a [Tweezers pick up a crystal from inside the dish.] little give it a little squirt, there we are, [Water sprayed on crystal held by tweezers.] bring it over here, and set it off to the side. Now you're going to want to grab a few of these crystals because again, these are the seed crystals you're going [Tweezers grabbing a few crystals, one at a time.] to use, and you might need a couple of attempts. So what you don't want to grab is something like this. This is not a single crystal this is a whole [Tweezers grab a clump of crystals that looks like rock candy, with many bumps.] bunch of crystals crusted together, so you don't want to pick up anything like that. Okay, now that we've retrieved a few of these crystals and gently patted them [Benedict in lab.] off with a paper towel, we'll take a look at what we've got. You see this little collection here. The crystals all have very nice flat surfaces, sharp edges. [Crystals on black surface, each less than half the size of a dime.] They're nice and transparent or clear. It's a really nice little collection. Now the thing is, these crystals are just a little bit small. In fact, here's a previous attempt. You can see that it's a much larger crystal, and this would be a [Benedict holds crystal about the width of a dime.] seed crystal that you guys at home could very easily grow. I know that you can grow seed crystals better than this, and again, the larger the seed crystal you can grow, the better off you'll be in the next step of the experiment. And that's going to conclude our first video. We now have our seed crystal. The next [Benedict in the lab.] video will show you how to take this seed crystal and turn it into a large [Benedict holds up seed crystal and a large crystal grown in past competition.] single crystal. So. Hope you enjoyed watching, and we'll see you in the next video! [Lighthearted music plays.] [University at Buffalo logo on blue background.]

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