FREE ESSAY ON MANUAL FOR RECRYSTALLIZATION

MANUAL FOR RECRYSTALLIZATION

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 solid
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