In part 1, the sample that was insoluble at room temperature Table 1 , but soluble when boiled was the one with water as the solvent. The first goal of the experiment was to identify a suitable recrystallization solvent. You may have started out with a 90-10 mixture of two solvents, or 1 to 1 mixture of these two solvents, 50 minutes later, it might be 75-25. If there are any big chunks in there, I can use a glass stir rod to break up those chunks because that is going to help dissolving. This is because of impurities assorted with the unknown compound.
You might even see it getting turbid. If we have a solid compound, what we are going to do is -- I will call that the crude material. Maybe you find you can easily produce a mixture of equal parts weight:weight of sodium chloride and sodium oleate. Regardless of crystallization method, the purity of the solid can be verified by taking the melting point. Therefore, each growing crystal consists of only one type of molecule, the solute. If the sodium oleate forms an amorphous solid when it comes back out of solution, we have precipitation.
Sodium oleate is less soluble in water than is sodium chloride, so most of it would not dissolve. Perform gravity filtration with fluted filter paper, a stemless funnel, and an Erlenmeyer flask if some parts remain insoluble. The best recrystallization solvent was determined to be water by observing solubility in different conditions. Sometimes we have colored impurities. And then, maybe you have someone here who can rinse them out with some clean solvent again, using ice cold solvent. That will be a place where it can start to grow as well.
Because if it is warm solvent, then when you put it in here, it might redissolve your crystals. It is a nice way to let it dry. That is totally a judgment call up to you. Once it cools, it will solidify because your compound is a solid. But we are just filtering off, put a little filter paper in here, we would be filtering off any insoluble impurity.
That is because that solvent combination is something that is more polar and something that is less polar, ends up being the ideal solvent system for your particular compound. Make sure it is cold, before you add in your charcoal. One problem that could happen in a recrystallization is that there is a very insoluble impurity. How do we choose a solvent? Again, a certain compound can be very different crystals, depending on the type of solvent that is used. If not, what do you need to do? Leave them on the Buchner funnel for a minute or two, as it draws in air, it is going to be drying your crystals because we want to wait and we want to analyze them.
Sometimes we are lucky and we are following a procedure and it tells you - recrystallize this from methanol or recrystallize this from ethyl. In addition, I have not given aid to another student on this assignment. Add just 1 ml of solvent at room temperature and there your goal would be that it should not dissolve. Assuming we do not have our colored impurity here, we have a colorless solution here now, and we do not have anything undissolved. Finely ground particles of the compound are also necessary for good heat transfer. If someone else has some of the product they have already isolated, you could take one of those crystals and drop it in there and that serves as a nucleation site.
The tube was then placed in an ice bath to further promote crystal formation. Then, you know you need to take action. Washing is simple to do. There are some techniques you can use to encourage crystal formation. The contaminant was successfully separated from the product. We need to have those crystals come out of solution.
Measuring Melting Points - The melting point of a compound is the temperature at which the solid is in equilibrium with its liquid. You can now place the flask in an ice bath to finish the crystallization process. But lower that volume, maybe lower it back down, sometimes you lower back down until it actually gets turbid a little bit, a little cloudy. Recrystallization is a method of purifying a solid. You have to make a judgment. An orange impurity was left behind and a white product was obtained using an ethanol-water solvent.