.. lid and liquid will require the filtration process. The collection of the compound will be usually in a flask or another beaker after the chemical reactions have run their course. Remember: it is important that the experiment is complete before the purification can begin or there would be nothing to purify. Filtration Once the chemical reaction are complete and the experimental procedures are over, the filtration of the crude product can begin. Turn on the water facet and allow the it to produce a vacuum in the hoses and throughout the system.
To test if there is a vacuum, the student should place their hand over the funnel and feel for suction. Now the student can slowly begin to pour the initial compound into the funnel very slowly. Pour the compound into the funnel in intervals or it will overflow. Allow for the filtrate to drain completely before pouring more of the sample. When that is complete, a liquid filtrate should accumulate in the flask and a solid sample should build up on the filter paper.
Repeat Filtration and cleaning If the student recognizes that there is more of the solid left in the filtrate in the flask, he or she should repeat the filtration using the filtrate. The next step is to clean the compound on the filter paper. This can usually be done with cold water so that it does not dissolve the solid or it can be done with a chemical solvent that does not dissolve that particular chemical compound. Such as using a nonpolar solvent for a polar sample. WARNING: OVER FILTRATION WILL CAUSE THE SAMPLE TO DISSOLVE.
BE CAREFUL! Collection and measuring of crude sample After the filtration is over, the crude sample will collect onto the filter paper. The student must be careful in removing the sample from the paper and placing it into another flask. At this time the student should record the weight of the sample and make calculations on the percent yield of the final product as compared to the results of a perfect experiment. The student may also choose to run certain purity tests. At this point come of the impurities will be left in the sample and the next purification step will try to eliminate those as well.
Chapter 4 Recrystallization Process The is a most crucial part of any Organic Chemistry experiment. It is also an amazing sight to watch these crystals form from a solution of just liquid. Solvent addition The first step is to prepare the particular solvent by heating on the hot plate. Once the solvent has almost reached its boiling point, it is time to begin adding it to the sample compound. Place the sample in a small 50ml flask and add the hot solvent dropwise onto the solid.
Dropping of the solvent must be done slowly because one drop will could cause the solid to dissolve, and an extra drop could cause the solid to not reform in crystalline form. Once again the student must take extreme care! Induction of crystals After the solvent completely dissolves the solid, recrystallization can proceed. Take a clean stirring rod and slowly scratch the inside of the flask containing the solution. Do not completely immerse the rod in the solution. The scratching of the flask will induce crystal formation to begin.
Remove the rod and watch as more of the crystals form in the flask. Take the flask and place it in a larger beaker or flask that is filled with ice. This will help promote more crystal growth Collection Allow enough time for the crystals to grow in the ice bath before collection of the crystals. Now the student should use the air stream setup to evaporate the rest of the solvent. The micropipette should have a slow stream of air coming out of it. Place the pipette above the liquid and allow it to blow onto it until all the solution is completely gone.
After this procedure, the student should once again begin to carefully remove all the solid crystals from the flask. Try to get as much as possible. Allow time for the sample to sit and dry as well. The student should record the weight of the purified sample and place it in safe place for further tests. This would be a perfect time for the student to perform more calculations on the purified sample.
Chapter 5 Evaluation Methods for purity Now it is time to find out if all the hard work has paid off. Hopefully, the recrystallization has removed most of the impurities found in the sample. If it has not, more purification method might be an option for the student to consider. Small scale test These test are of more generic method to find out what the sample is made up of. A melting point test can help determine the chemical formula of the product. Each chemical compound has a specific melting point, and a student can refer to these melting points in a reference manual provided in the lab.
Also, the tool used for melting point tests are also available in the lab. Another small test is Thin Layer Chromatography. Also know as TLC, this test can help determine other chemical compounds that might exist in the sample. The process of TLC is available in the other series of instruction guides titled, Identification Tests. More accurate tests The student or instructor to conduct more complicated test to determine the chemical nature of the product. This can be done using Infrared Spectroscopy or Nuclear Magnetic Resonance.
Both of these procedures require machines that give computer readouts on the nature of a sample compound. These tools provide exact measurements and formulas. Chapter 6 Frequently asked questions and troubleshooting Q: How do I know when the reactions are done? A: Follow the instructions, usually a color change or something will indicate that the reaction is over. Or ask the instructor Q: Can I skip the Recrystallization process? A: This process does not have to be done if the student has achieved a sample that is pure after filtration. However, this is highly unlikely.
Q: How do I know when the filtrate is completely clear of product? A: This is a judgment call. The student should look to see if there could be more product left to filter out. Try to do the filtration at least twice. Q: What if know crystals form? A: Keep scratching the glass using the rod. Or try and place the flask in the ice bath earlier, that may induce crystal formation. If nothing happens the solution have been solvated too much to allow the crystals to reform.
IF ALL ELSE FAILS, ASK THE INSTRUCTOR FOR HELP! INDEX Crude sample Collection Equipment Filtration Glassware Induction Infrared Spectroscopy Melting points Nuclear Magnetic Resonance Organic Chemistry Recrystallization Safety goggles Solvents Sterilization Thin layer chromatography Vacuum.