Instruction Manual The purification process: Recrystallization & Filtration Jason Williams 09-13-00 NATS 4310 Table of Contents Preface Chapter 1 Equipment involved and preparation Glassware and accessories Proper sterilization of equipment Safety precautions Chapter 2 Setup procedure before purification Equipment setup Choosing of solvent Chapter 3 Gathering of an unknown compound and the first step: filtration Collection Filtration Repeat Filtration and Cleaning Collection and measuring of crude sample Chapter 4 Recrystallization process Solvent addition Induction of Crystals Collection Chapter 5 Evaluation methods for purity Small scale test More accurate tests Chapter 6 Frequently asked Questions and trouble shooting Index Preface To begin, the intent of this booklet is to give instructional advice. The instructions given will provide a basis to allow an individual to perform the necessary task to undergo the purification process. The design of the manual is to instruct students in a college laboratory setting. In particular, the area of science that the manual will focus on is Organic Chemistry. Students will be able to refer to this instruction guide throughout the semester because this process will be put in use often.
The purification process if an essential part of chemistry, and the student must recognize its importance. Without a purified product, many of the drugs on the market would not be on sale. Even though these purification procedures are on a small scale, it will provide a starting point for those who are just beginning Organic Chemistry. The skills needed to purify a product will come with practice and help from the instructor, but this manual will give the initial directions to help the student on purification. Once mastered, more techniques will help the student to gain a product that is pure enough to put on the market. Chapter 1 The Equipment involved and preparation The first step in understanding any laboratory process is understanding the equipment needed.
Also, there is a need for the proper preparation of the tools needed before any of the steps can begin. Glassware and accessories The main pieces of glassware needed to conduct the filtration and recrystallization will be at least two 250ml flasks, a 100ml flask, and at least three 50 ml flasks. In addition, a glass stirring rod and a case of micropipettes would be useful. For the filtration procedure, a funnel with a rubber stopper, a trapper flask, and a small piece of filter paper is important to have. There is also a need for vacuum hoses in the filtration process as well. The student will also need a hotplate.
The lab will provide all the necessary pipes needed to setup a vacuum and also the air current needed later on in the collection phase. Each lab will have different types of equipment, and it is the students responsibility to understand and learn how to work each tool. Proper Sterilization For any experiment to have the proper results, cleaning and sterilization is critical part of preparation. The best way to have the glassware cleaned is to steam clean the many pieces in a autoclave or a dishwasher. This may be done in advance by the instructor or the students.
It is also good practice to clean the equipment by hand, even after it has come out of a machine cleaner. The funnel and the filter paper must also be free of any impurities so that it will not reflect in the result. Because the purification process is so important, there has to be a high standard of cleanliness for all the tools that the student will use. *It is extremely important that the student make sure all the pieces are dry as well or the weight of excess water will show up in the results. Thus exaggerating the final calculations* Safety Precautions Above all else, it is important to take all the proper methods to be safe in the laboratory. All Students must wear safety goggles at all time in the lab.
It would also be a good idea to wear pants and shoes in case of spillage. Also, the student might also consider wearing gloves, but the instructor will notify the student if the chemicals require a student to wear gloves. It is also important that all safety related issues be reported to the instructor immediately. WARNING: DO NOT TRY TO CLEAN UP CHEMICALS WITHOUT NOTIFYING THE INSTRUCTOR Chapter 2 Setup Procedure before purification The setup for the process is simple, but choosing the right solvent to do the job is critical. Equipment Setup The setup of the glassware for the filtration procedure is as follows. First one hose must be firmly on the vacuum pipe on the water facet in the lab. The other end of the hose will go to a flask will connect to the top end of a trapper flask. ( The purpose of the trap is prevent water from the pipe to flow into the filtrate after the process is complete.) Next the on the side of the trapper flask is a small projection for another hose.
The other end of this hose will go to the 250ml flask with the vacuum projection on the side. This is the flask where the filtrate will fall into. Place a funnel with a small piece of filter paper in on the top of the flask. Make sure a rubber stopper is on the top of the flask as well in order to have a proper seal. The only other setup required is for the air drying process that is done in the collection phase after recrystallization.
A micropipette attached to a hose, which will provide a stream of air to allow the solvent to evaporate off of the crystals. The air stream will come from the pipes in ventilator hoods in the lab. Choosing of Solvent The most crucial part of any recrystallization is the need for the correct solvent. It is important because it must dissolve the crude sample while it is hot but not when it is cold. In addition, it must dissolve the impurities in the sample at both temperatures, so that they remain in solution.
This process is usually a matter of trial and error. However, the instructor may have already chosen the solvent before hand. Students should refer to their textbooks and understand the concepts of polarity and solvation before they proceed to choose a solvent. *If problems arise ask the instructor for help.* Chapter 3 Gathering of an unknown compound and filtration Without proper filtration, the rest of the purification steps will be pointless. It is crucial that the student take care when transporting the sample from each piece of equipment to another.
Collection The collection of the initial sample will come after the student has gone through the desired experiment. Experiments that end in a final compound that is a mixture of so …