Recrystallization of Cream of Tartar

Added: 2026-05-07

[00:00:25]Hello, my name is Dr. Eszter Trufan and in  today's experiment I am going to demonstrate how to do a recrystallization of cream of tartar.  For this we're going to need potassium bitartrate or cream of tartar, and we're going to use water,  because there is a substantial difference between the solubility of cream of tartar at room  temperature and its solubility at the boiling point of water. It is a very suitable approach  for the recrystallization of cream of tartar, because we're going to take advantage of  temperature differences. It is important that we use a hot plate to heat our water.  I have a hot plate here. We're going to turn this on and then hike its temperature. We  want to be above the boiling point of water, which is 100°C. Some heat is always lost to  the environment, so, I am setting it to 113°C.

[00:01:21]Next, I'm going to use a relatively large 600  mL beaker because I need to know the mass of the cream of tartar that I'm putting inside.  I will use a scale. And I will need to know the volume of the deionized water that I'm  using for the experiment. I'm going to use a 100 mL graduated cylinder. First, I'm going  to turn on my scale, place my beaker on top, tare it, and when it shows 0.00, I am  ready to add 18 g of cream of tartar.

[00:02:01]We can be a little over or a little  under, but we should not exceed 18.3 g.

[00:02:12]I have 18.15 g of cream of tartar.  This is pretty good. I can set my scale to the side, and I am ready to add my water.

[00:02:27]First, I measure out 100 mL.

[00:02:32]I want to be just under the 100  milliliter mark. 99.2 milliliters.

[00:02:44]I add another 100 mL increment.

[00:02:54]And again, I want to stop just under the marking.

[00:03:00]If it's a little too much, I can always  extract it. The meniscus of my water is exactly at the 100.0 mark. I will pour this over and then I will measure a third 100 mL amount.

[00:03:24]It is quite close at 99.8 mL. I  will pour this into my large beaker and we can swirl it around a little bit, but  we can see our mixture is extremely cloudy. And that is normal because cream of tartar is quite  insoluble at room temperature. That will change when the temperature goes up to the boiling point  of water. So we take our beaker with the cream of tartar mixture and then we begin heating our hot  plate and hopefully as it gets to the boiling point of water, it is going to dissolve  all of it and our mixture will turn clear.

[00:04:06]With more vigorous stirring and heating, the  temperature of our mixture is increasing. And we can already see that the cream of tartar  that was on the bottom of the beaker is not quite there anymore. And while we do see  lots of small particles floating around, it looks a little bit more  clear than it was before.

[00:04:30]It has been some time since we started warming  and stirring the cream of tartar inside the deionized water, and we can see that the mixture  is starting to clear up. There is still a little bit of fine powder on the bottom. But as long  as the mixture is boiling, that should dissolve and the mixture should clear up forming a clear  solution, unless there have been some additives in our container at which point the clarity will  not be achieved. So, we want to make sure that the solution comes to a vigorous boil. If at that  point it is completely clear, we just set it aside and let it cool slowly. The slower the better.  However, if when it's boiling and it has boiled for at least 10 or more minutes and clarity still  has not been achieved, that means that there have been additives in our container and we need to do  a very fast filtration. Which means that our only option, at that point, will be Buchner filtration that  needs to be accomplished in as little time as possible with the boiling hot liquid. But with  this mixture, we can already see that clarity is slowly getting achieved. And what we see on  the bottom are more combinations of bubbles that are coming from the boiling and a little bit  of powder still moving around. So, we're going to keep it going for just a couple more minutes  and then we're going to make a decision for this.

[00:05:56]Our solution with the cream of tartar is clearing  up. The solution is boiling. So that is pretty great. And when we look at it, there's barely  anything on the bottom. But if we give it one or two more minutes, it will completely clear  up. If this is not your experience when you're boiling this solution, then you need to do that  hot filtration. But if your solution cleared up like this, it is fantastic. That means that the  cream of tartar from your container was pure, and from there you can proceed with the  crystallization. Because there is such a large difference in the solubility of cream  of tartar at the boiling temperature of the water and at room temperature when dissolved  in water, once we take it off the hot plate, it will very quickly produce crystals. Even if  you just lower the temperature by a little bit, it will start producing precipitate or crystalline  material. So that is why it is so important that you keep your cream of tartar in water going for  at least some time before you draw any conclusions about the purity of the material. Now that all  our material is fully dissolved, our solution is clear. I can simply turn down the temperature.  And as I turn down the temperature, we may already start seeing crystallization. But if that doesn't  happen very quickly, we can just put it on some kind of surface that is insulated to make sure  that our bench top does not get burned or that we don't accidentally place it on top of a water  droplet causing our beaker to shatter. And then we need to restart our experiment. Very slowly,  let it cool down. The slower the better because that determines the quality of your crystals.  If the cooling happens over the course of 24 hours or even longer, that's better and you  should expect to see beautiful shiny crystals.

[00:07:59]Our solution has been cooling for some time and  this is after 24 hours. We heated it up. It turned into a clear solution. Then we cooled it down  because the solution was cleared. If the solution was not clear, then we need to do a hot filtration  really, really fast. And that means we're going to use Buchner filtration. After it cooled down,  we have a lot more options. You can see that the solution is rather clear and on the bottom there  are really nice looking crystals. We don't really care about how they look, but we do care that when  they are crystalline, they are more pure than they were in their powder forms. So, we're going to do  a filtration. Here you may do a Buchner filtration or a gravity filtration. Today, I am going to  demonstrate the gravity filtration. For this, you're going to need a stand with an O-ring.  And inside that O-ring, you're going to place a funnel. Make sure the O-ring is the right  size to support your funnel. Under the funnel, there should be an Erlenmeyer flask. This will  catch your filtrate. And ideally, the stem of the funnel should be just under the rim of your  container. If you don't have an Erlenmeyer, you may use other containers. Because we're doing  a filtration, we're also going to use filter paper. I will use one a large filter paper. And  I will fold it as usual in half, create a crease, and then in half again, and this way I have neat  quarters. I will create another crease. Then I will open it in such a way not in half. So on one  side I have one layer of the filter paper and on the other side I have three layers. This will give  me a nice cone shape. If I place this cone shape into my funnel and just let go, it will jump out  at me. So, the next thing that I'm going to do is add just a couple drops of my solution into my  filter paper. This way, when the filter paper is wet, it sticks to the sides of my funnel. And  now, we can begin filtration. I will add plenty of solution to my funnel. And because the top is  rather clear solution, it will go through rather quickly. If we find that this is a little higher  than we prefer, we can lower it a little bit more.

[00:10:35]Because we're working with a large volume  of solution, we want to keep the top layer as clear as possible to help  with the speed of the filtration.

[00:10:46]And then when we get closer to the  bottom, we're going to swirl it a little bit more vigorously to get  all the crystals into our funnel.

[00:11:02]When we are pouring solution into the  funnel, the important thing is not to exceed the rim of the funnel, otherwise  it is going to spill out on the sides.

[00:11:12]Once our solution is mostly transferred and our  crystals are still hanging out at the bottom of our large beaker, it is time for a little bit  more intensity as we pour things over. So, we want to swirl our contents and then very  quickly transfer it over. If something spills, that's okay. The majority of our content is in  the crystals and the crystals may be collected.

[00:11:46]If we're still struggling with  the transfer of our contents, we can always employ the help of a  spatula and scrape everything inside.

[00:12:06]We are close to done, but not quite. It is always  a good idea when we're doing recrystallization and then filtering off our filtrate to rinse  our crystals with small amounts of the ionized water. So we add small increments into our  beaker. Make sure that we are swirling vigorously so that our crystals are moving around and then  rather quickly transfer them into our funnel.

[00:12:40]We'll do this at least one more time to rinse our  beaker completely and transfer all the crystals.

[00:12:50]If we need to, we can do it a third time.

[00:13:00]Swirling vigorously and then very quickly  transferring so that our crystals stay kind of floating around a little bit. And then  finally, we add at least one or two small increments of water onto our filter paper  to make sure that all our solution is washed both from around the crystals and from the filter  paper. Then one more time with a small increment.

[00:13:30]And from there, we let it drip until all our  solution goes through and only the crystals are left at the top. Now, for these crystals, because  they are rather temperature sensitive, I do not recommend that we put them on a hot plate and dry  them as other materials. It is best to take these, place them on a watch glass or a small container  and let them air dry over the next couple days.

[00:13:58]It has been about 24 hours since I left my  crystals of cream of tartar to dry on the filter paper.

[00:14:06]Remember, I don't want to heat this because it  will undergo some decomposition processes. So, for now, I'm just going to leave it as is, it air  dries. So, it is as dry as it can be. And next, I am going to weigh it. And then I'm going to  put it in a container for later. I'm bringing in my scale and I am going to bring in my  container. I am going to turn on my scale, tare it, and when it shows 0.00, I will  place my filter paper with the cream of tartar crystals on the top. I will record  my mass, which is 19.32 g. At that point, I will open my container, transfer all  the crystals of cream of tartar into it, and then weigh my empty filter paper. The  mass of my filter paper is 2.72 g. The difference between the two measurements  is going to be the mass of my cream of tartar.

[00:15:17]And now that I have pure cream of  harder crystals, I am ready to take on experiments that will require pure cream  of tartar to produce a different product.