Organic Chemistry: Isolation and Purification Lab
Lead Author(s): Louis R. Nudy, PhD
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This manual contains experiments ideally suited for a first semester college level Organic Chemistry Laboratory course. Experiments are best suited to be completed within one or two 2.5 to 3 hour class periods. The experiments include the most commonly required basic isolation and purification methods used in the organic chemistry laboratory. The introductory section for each experiment fully explains the basic chemistry involved in the structure activity relationships that are used in each experiment.
1. Introduction to Organic Chemistry Laboratory I
1.1 Getting the Most from a Laboratory Course
One of the purposes research chemists have for conducting laboratory experiments, is to test their theories about how molecules and samples of various materials behave, change physically or chemically, and react under various controlled conditions. If they design their experiments well and make careful observations and measurements, they may discover something new that may, or may not, corroborate or support their theories. Many scientists report that seeing and observing directly for themselves, under carefully controlled conditions, is very gratifying. Even when everything does not come out as was expected or hoped, it is just as gratifying if you learned something new about the substances you worked with. Scientists also warn to not let any expectations or hopes about outcomes, that you may have before conducting an experiment, obscure the accurate, careful, and detailed observation and recording of both what you did, and what happened, as you complete each step of an experiment.
The purposes we have for asking you to conduct the experiments in this laboratory include everything listed below. All are of value and are presented in no particular order of importance.
- Allow you to demonstrate and practice good, safe chemical laboratory techniques.
- Provide you the opportunity to find gratification when directly observing the outcomes and results of experiments that you made happen directly by your own efforts.
- Improve your ability to follow detailed procedures accurately, precisely, and safely with the equipment made available to you.
- Understand the hazards of chemicals and the practices you must take to minimize the risk of harm to you, those around you, and the environment (e.g., flammability, corrosion, dermal absorption, toxicity).
- Directly observe, through your own activity, some of the variety of physical changes and reactions of chemicals that you have learned through the Organic Chemistry texts and lectures.
- Thinking critically and presenting a discussion in your lab report about what you observed and measured, and the degree to which these observations corroborated, or did not corroborate, the stated purpose of the experiment, or what you may have expected.
- Identifying the theories you learned that were exemplified in carrying out the procedure and noting all observations and data.
- Writing a lab report in such a way that anyone can reasonably be expected to repeat what you did and be expected to make the same observations as you made. More details will be covered in Expectations for Lab Reports.
1.2 Safety, Hazards and Risk in the Chemical Laboratory
Safety in the laboratory includes all the actions we take, and all the safety equipment, devices and personal protective clothing we use to mitigate the risk of harm from chemicals.
It is important when discussing safety in the laboratory to recognize the difference between hazard and risk. Hazards are the properties of chemicals that put us at risk of harm. We can’t change the hazards of the substance itself. But, we can change the risk of those hazards causing us harm by taking protective actions.
In order to reduce the risk of harm we must first recognize the hazards of the chemical we use.
"A Guide to The Globally Harmonized System of Classification and Labeling of Chemicals (GHS)", available on-line from OSHA, includes the following list of classes of hazards separated into physical, human health, and environmental hazards.
1.2.1 Physical Hazards
Explosives • Flammable Gases • Flammable Aerosols • Oxidizing Gases • Gases Under Pressure • Flammable Liquids • Flammable Solids • Self-Reactive Substances • Pyrophoric Liquids • Pyrophoric Solids • Self-Heating Substances • Substances which, in contact with water, emit flammable gases • Oxidizing Liquids • Oxidizing Solids • Organic Peroxides • Corrosive to Metals
1.2.2 Health Hazards
Acute Toxicity • Skin Corrosion/Irritation • Serous Eye Damage/Eye Irritation • Respiratory or Skin Sensitization • Germ Cell Mutagenicity • Carcinogenicity • Reproductive Toxicology • Target Organ Systemic Toxicity – Single Exposure • Target Organ Systemic Toxicity – Repeated Exposure • Aspiration Toxicity
1.2.3 Environmental Hazards
Acute aquatic toxicity • Chronic aquatic toxicity • Bio-accumulation potential • Rapid biodegradability
These hazard classes were adopted by OSHA to help with efforts under the UN to have all nations begin to use common means to communicate hazards, protective measures, and certain emergency response actions.
1.2.4 The Safety Data Sheet
One of the means to communicate chemical hazards required by OSHA is called a Safety Data Sheet (SDS). SDS’s are available for all chemicals you use in the laboratory and your instructor can tell you all the means available for you to access them.
With misuse, even a chemical that is considered harmless can cause injury or even death. This is why it is always good to learn more about each new substance you use.
For example, fatal outcomes form drinking even too much water have occurred. According to an article by Tamara Hew-Butler, PhD, FACSM, In a CBS News online article, she explained that hyponatremia is caused by drinking too much water or sports drinks, which dilutes blood salt levels below the normal range. Any sudden drop in blood salt levels, from drinking more than the body can excrete, can cause all cells in the body to swell.
Read the article here:
Which of the following is a risk but, not technically, the statement of a hazard?
High flammability classification of a substance as measured by its low flash point temperature
The ability of an acid to be corrosive to skin and tissue
Students working in an academic Organic Chemistry Lab
Toxicity of a substance to marine organisms as measured by a very low concentration in water that is lethal to 50% of the Daphnia Magma organisms (1 to 1.5 mm crustacean) in test population.
1.3 Safety Rules
1.3.1 Know Hazards, Precautionary Measures, Personal Protective Equipment, and Emergency Response
As stated above, a first step to minimizing risks is knowing the hazards and risks of the chemicals you intend to use. Throughout the rest of the text you will be reminded of some the most serious hazards of some of the chemicals. Your instructor will also underscore the hazards.
Consult other sources such as the SDS. SDSs should be available to you in the lab. Section 2 of the SDS summarizes the hazards. You can also access International Chemical Safety Cards (ICSC) via the CDC supported website: https://www.cdc.gov/niosh/ipcs/default.html. As stated on the site, “These cards contain the collective views of the ICSS Peer Review Committee and may not reflect in all cases all the detailed requirements included in national legislation on the subject.”
Besides knowing the hazards, do the following listed below, and read the subsection for each item that follows.
- Know emergency response procedures & equipment,
- Remove yourself from the danger and warn others,
- Do not try to contain a spill or fire unless you are certain you can do so without any further risk to yourself and others,
- Notify your instructor who will take appropriate action,
- If there is an immediate threat of injury, or your instructor cannot respond, call 911 or campus emergency services,
- Know your address and building in case of such an emergency.
1.3.2 Know the Emergency Response Equipment and its Location in the Lab
Fire extinguisher: Review the types of Fire extinguishers at the following: https://www.osha.gov/SLTC/etools/evacuation/portable_about.html
Watch the video below courtesy of Howcast on how to use a fire extinguisher. Always consult your instructor on how to proceed in event of fire.
Emergency Eye Wash: All laboratories are slightly different so it is important that your instructor shows you where each eye wash station is located. You must know exactly where the closest eye wash station is relative to where you are working. Corrosive substances can damage eyes quickly so you must flush immediately if you get any substance in your eye; especially those are corrosive (ex. strong and bases and oxidants). Keep flushing until your instructor comes your aide. It is very important to not let up on continuous rinsing. Your instructor will tell you when to stop and refer you to additional aide or check up.
Emergency Shower: This should only be used when the sink or eye wash does not provide for adequate drenching of the area exposed to acutely hazardous or corrosive chemicals. Keep in mind that you, and all near you, will get drenched.
Select the class or classes of fires for which the fire extinguisher in your lab is approved?
Class A, ordinary combustibles
Class B, flammable liquids and gasses
Class C, live electrical equipment
Class D, combustible metals and metal alloys
1.3.3 Know and Use the Engineering Controls Correctly
Engineering control refers to equipment used to contain chemicals, or abate risks of contact with incompatible materials, or the risk of hazardous exposure to you, others, materials, and the environment. The engineering control you will use most frequently is the fume hood. All hazardous chemicals must be kept and used within the fume hood during the entire lab. Place only your hands into the lab fume hood, and keep it closed as completely as possible while working with the glassware or apparatus that is in the fume hood. The more the sashes of the fume hood are left open, the higher the risk of inhalation of gases, volatile liquid chemicals, or dust from solids. Best practice is to only raise the hood shield enough so that your face is still shielded by it, and reach in underneath to do the work needed. Also, keep all hazardous chemicals at least 6 inches from the front of the hood.
1.3.4 Use Protective Clothing
Avoid all contact with all hazardous chemicals in the lab (i.e., ingestion, inhalation, skin or eye contact).
You must use safety glasses with side shields in all cases, and you must use googles when using corrosive materials (e.g., HCL and NaOH ), material readily absorbed by skin (e.g., DMSO), or chemical that otherwise could cause severe skin or eye damage or reactions (e.g., allergens).
Protective gloves must be worn when transferring all highly hazardous chemicals such as skin adsorbents, corrosives, carcinogens, reproductive toxins, and sensitizers. Remember that few glove materials are completely impervious to all types of chemicals. Contact of all chemicals with gloves is to be avoided. Making slow careful transfers, with appropriately sized glassware for the task, will help prevent spills and contact with the gloves. Gloves should be considered only temporary and minimal protection. Consequently, change gloves when there has been more than minimal contact of the gloves with the hazardous chemicals, or if there are any tears.
You must wear long sleeved shirts or blouses, long pants or dresses, shoes and socks to prevent any directly exposed skin other than face and hands. Shoes should cover feet completely. Sandals, flip flops, or other open shoes are not acceptable in the lab. Avoid shoes made of obviously very porous materials such as cotton or wool.
A laboratory coat or apron is highly recommended to protect your clothing and as another layer of protection for your skin.
1.3.5 Reduce Clutter
Ironically, some accidents that occur in the chemical workplace are often unrelated to the chemical hazards. Tripping hazards, for example, contribute to serious injuries. Keep all coats, book bags, backpacks, and anything else off the floor. If you can’t find a safe or large enough place for these items, ask your instructor. There is plenty of additional storage that may not be at your work station.
Always cap chemical containers if you need to temporarily remove them from the fume hood. Make sure you hold them securely and your path is clear. You should not be carrying any bottles of corrosive chemical around the lab unless your instructor approves and has provided a non-corrosive rubber secondary container.
Reduce clutter where you are working. When you are done with a piece of lab glassware, place it towards the back of the fume hood away from you and the equipment you need to use next.
1.3.6 Separate and Collect Waste
Keep a beaker or Erlenmeyer flask in your hood to use for waste. Have a separate container for each type of waste and label it as one of the following, along with the experiment name or number: a) dilute aqueous acid, b) dilute aqueous base, c) non-halogenated organic, d) halogenated organic, or e) specific chemicals assumed or known to be of relative high purity (e.g., recovered solvent after distillation or rotary evaporator use).
At the end of class, ask your instructor where you may combine waste with that of others in the class, for disposal by the college. Never remove chemicals, including waste, from the laboratory.
1.3.7 Do Not Bring any Food or Beverages into the Lab
No one plans on an accident. And of course no one should be expected to use a food or beverage container for chemical disposal; but it did happen in a lab. Maybe because others don’t expect anyone to bring containers for anything but chemicals into the lab. A student once placed caustic sodium hydroxide solution in another student's water bottle that had little or no markings on it. The student thought the bottle was empty trash, and thought that it was safe to use it just for a moment until he could ask where to properly dispose of chemical. The owner of the bottle returned and drank it before the student could tell him or stop him. The student needed emergency care and was treated for severe burns to the mouth and esophagus.
You may think a certain accident is unimaginable, but many thought that until they were involved in an accident. The potentials for contamination are plentiful and insidious in the lab. It is not a hardship to leave food and beverages outside the lab. The safest practice is to NEVER BRING FOOD OR BEVERAGES INTO THE CHEMISTRY LAB.
1.3.8 Do Not Use Unapproved Chemicals or Use Approved Chemicals Under Non-approved Conditions
Never mix chemicals you were not specifically instructed to mix, as stated in the procedure, or as approved by the instructor. Since most of you are at least second year students, you might be able to think of several obvious incompatibilities like adding water to strong concentrated acid and bases. But many are not obvious. The SDS should also list incompatible materials in section 7 and or section 10. For example, when sodium sulfide is mixed with an acid, deadly H2S fumes (a deadly gas) are produced.
1.3.9 Keep Minor Spills Minor
Even spills that do not pose an immediate risk of harm to others must be reported to your instructor. Your instructor will work with you to approve the appropriate, safe, and effective remediation of the spill as appropriate for the hazards. Spills of hazardous substances must be reported to your lab instructor immediately. Do not try to clean them up without instructions from your instructor that will be appropriate for the specific hazard.
You may try to contain spills with barriers only if there is absolute certainty of NO risk of exposure to you or those around you in doing so. It is better to not turn a mistake into a disaster.
1.3.10 Never Remove any Chemicals from the Lab
Regardless of hazards, or lack of hazards, your removal of chemicals from a laboratory is a safety negligent act, since non-hazardous chemical could have been contaminated. You are criminally liable if you remove chemicals from a lab and you are not a trained and authorized staff or faculty member.
1.3.11 Be on Alert Against Risky Behavior
Reminding a fellow students about gloves or safety glasses is an example of what you do when being alert to risky behavior. Be your own protector as well. Always think about how you can do something more safely, and discuss it with the instructor, if you are not sure a planned action is safe.
For more details on hazards and safety in undergraduate chemistry lab consult the following provided by the American Chemical Society:
Have you read and understood the safety rules?
Need help understanding
Which of the following are acceptable in the chemistry laboratory?
Food and beverages or their containers
Storing back packs or any other items on the floor next to your bench
Wearing open toe shoes
Using chemicals other than those explicitly instructed to be used in the lab manual or by your instructor
None of the above
1.4 Expectations for Your Lab Report
There are many different acceptable formats and rules you will encounter for writing lab reports for different purposes, such as those required by the publisher of a scientific journal, or those required by an employer. While there are some things in common compared to reports you wrote for other courses or for a job you had, you must use the format described below, for this course, in order to receive maximum credit for each lab.
Since your reports must be graded, it is important that your instructor can grade each single student's report in a manner that is most consistent with how all others are graded. When all students follow the same format, it eliminates one variable that may contribute to grading based more on style and organization differences, than on the quality of the technical content.
It is also worth noting that this format differs from the American Chemical Society (ACS) general guidance for publishing a research report intended for submission to chemistry journals. If you would like to see the differences and similarities, consult the ACS Style Guide: Effective Communication of Scientific Information, Coghill, A.M., Garson, L.R.; 3rd Edition, American Chemical Society, Washington, DC, 2006. The format that follows is intended to include the collective content and general order of what is reported.
You will be graded primarily on the quality of the content you create and cite in your lab report. You will also be graded based upon your adherence to the guidelines that follow unless your instructor has given you a different unique exception to follow. Thus, you may lose points for otherwise correct content if you fail to adhere to the standard format below.
Every lab report must be divided into the numbered sections that follow. The headings of each section in bold below must be included in each and every report before completing the respective section. This provides the reader with a clear break between the beginning and end of each section.
Copy title exactly it as it appears in this text.
After reading the entire lab in this text, write an introduction in your own words with occasional use of footnotes including any source you may have consulted besides this text. The introduction should only be about two paragraphs, each consisting of a maximum of 5-6 sentences. Include some or all of the information listed below, as concisely and thoroughly as possible. What you include will depend upon the specific experiment. You can also vary the order as appropriate, and based on how you feel it flows best.
- Include the name of the lab method or technique, type of reaction, mechanism, or analysis that is the main purpose of the experiment to be done.
- Make sure to include all the the names of the unique new chemicals or equipment you will be using to carry out the main separation, measurement, reaction or mechanism that is part of the main purpose of the experiment and you are doing for the very first time during the course. Include the name of any chemical product(s) you intend to synthesize. Include only the method(s) or techniques that you will be using (e.g., distillation, extraction, re-crystallization, chromatography, spectroscopic method such as FTIR, HNMR, or CNMR) for the first time during this course, or that are critical to demonstrating the success of the experiment. Be as specific as possible. For example; state liquid-liquid acid/base extraction, instead of just extraction.
- Do not list every chemical or every technique or procedural task if used before for a similar purpose. Focus upon what is new and unique to each experiment in the report for that experiment.
- Make sure you include a very basic definition of the main lab method(s) or technique, type(s) of reaction(s), mechanism(s), or analyses that you as included in the preceding items, 1 and 2. Site references used that you found most concise and which you felt help you best understand the topic.
- If carrying out a chemical reaction include a sub-section showing the balanced chemical equation and organic reaction mechanism. Organic reaction mechanisms should include structures of all reactants, solvents, intermediates, and products theorized to be involved. Arrows for electron transfer must be included and used correctly.
Consult any contemporary Organic textbook for other examples of drawing organic reaction mechanisms and or the following video:
3. Chemical and Properties Table(s)
The table(s) is/are for listing all the major chemicals you will be using and any products you expect. For example, when you plan to perform a chemical reaction in an experiment, all substrate, reagent, solvents, product expected, and catalytic chemicals should be included. Include the common names (as they appear in the manual), and also provide a skeletal structure for each substance.
For each chemical name there should be a column with each of the CAS number, melting point (MP), boiling point (BP) (not necessary for salts), specific gravity, and any other property you are specifically required to measure during the experiment, or which may reasonably be used to evaluate that your product is as intended. Some examples of such include, relative water solubility, relative polarity, and or major spectroscopy features you may be investigating.
Although your instructor may provide some of this information for your use, you remain responsible for completion and clear organization of the information into a table.
This is not a table for recording measurements you make. This is for reference purposes when conducting the experiment, and for making comparisons of what you observe to what is already reported in the literature. Remember, the experiments you are doing have already been done by many others. It is up to you to determine which properties or reported outcomes expected for the experiment you were and were not able to reproduce. Keep in mind, there may be physical limits to how well you can reproduce everything expected, or how well you can measure certain properties accurately. In other appropriate sections of your report honestly record your observations, measures, and or data. In the discussion section of your report explain why you may not have been able to observe everything expected or why measures were not in 100% agreement with values known.
Good resources of known data on chemicals are listed below. Be sure to cite the references for anything in your report you obtain from these references, or other sources from which you may need to copy data or a statement.
- CRC Handbook of Chemistry and Physics, 99th Edition, 2018-2019 ISBN 9781138561632 - CAT#K43481 http://hbcponline.com/faces/contents/ContentsSearch.xhtml
- NIST Chemistry WebBook, SRD 6 https://webbook.nist.gov/chemistry/name-ser/
- US EPA https://comptox.epa.gov/dashboard
- PubChem-an open chemistry database at the National Institutes of Health (NIH). https://pubchem.ncbi.nlm.nih.gov/search/
- The European Chemicals Agency, ( “ECHA”) maintains this website https://echa.europa.eu/information-on-chemicals
- Spectral Database for Organic Compounds SDBS https://sdbs.db.aist.go.jp/sdbs/cgi-bin/cre_index.cgi
Before each experiment read the procedure through once to get a basic idea of the flow of the procedure. Then reread it carefully and thoughtfully while pausing to ask yourself if you understand the purpose of each step and how each step relates to the overall objective or purpose. Ask yourself if how you perform each step is going to be critical to the outcome. For example, if the procedure states the specific rate at which to add one reagent to another, make sure you understand what would happen if your rate was too slow or too fast, and how precise adherence to the rate needs to be.
Thinking as described above will take time the first time, but you will get faster as you practice. It will help improve your focus and attention to detail as you perform multiple experiments.
Make sure that you have a photocopy, or access to the original copy of the procedure, with you in lab when performing the experiment.
Focus on completing the experiment as exactly as intended and refer back to the manual as needed to double check details. Document that you followed everything as per the manual up to the point where you may have become uncertain or realized you had not.
In writing any original report of an experiment you performed in the lab, it is important that you honestly, accurately, and thoroughly report exactly what you did. However, as you are doing the experiment you should be following the procedure written here as closely as possible. You should have also thoughtfully read the experiment before lab. Even if your instructor tells you to write the procedure in your own words in your lab notebook or in a draft report, refer to the direct procedure as written in this manual. Be alert to record any adjustments of details your instructor may provide during lab. Again, for the final report, report all you actually did as if you need someone else to repeat the experiment exactly as you did it. You may be surprised how many times you will find yourself thinking you understood the instructions, only to question them once you are in the act of doing it. Make notes related to new details about how to carry out the procedure as you learned them in lab.
To summarize, in this section of the report, simply list the sequence of actions you took as you made them. Make certain to note any step(s) that you did not carry out exactly as specified, or that you are unsure about. You can add an explanation as needed, but do not substitute unless your instructor agreed to a modification. It is a better use of your time and thoughtfulness for you to learn to express what you actually did rather than just copy from the manual.
For anyone to follow your work, they need to know exactly what you did or did not do.
Although you should not deviate from which chemicals and which conditions are applied for safety reasons, you will discover that minor unanticipated deviations from exact rates of conditions, or size of vessels of use might need to change depending upon how things progress. For example, you may need to repeat a filtration, distillation, or re-crystallization. Always ask your instructor before making alterations, and don’t be afraid to admit when you think you may have done a step incorrectly. If you observe something not expected, record it, and ask your instructor about it. These are the opportunities unique to doing a lab. Real-time, hands-on learning, is often better remembered than just reading about it.
Also record any deviation from the procedure and describe it as detailed as possible. For example, you might say, "I realized I had used a Buchner funnel for the second filtration instead of a gravity funnel that was specified per the lab manual for the filtration of the mixture I obtained after having mixed my impure sample with hot water and a de-colorizing agent." Be as specific as possible so you and the instructor will know later exactly when and where whatever you did differently. However inconsequential you may think it is at the time, there may be something you missed. Don’t speculate or report what may or may not have happened as consequence of the deviation in this section of the report. Save reporting what you observed for the observation section, item 5 below. Save any interpretation as to why what was observed, was or was not expected, or how this may have impacted results for the discussion section, item 7, below
5. Qualitative Observations
Get in the habit of reporting sequentially during the lab what you observed at each step and especially during any deviation or anything unexpected. Separate direct qualitative observations from quantitative measures. Report quantitative measures in the next section.
Focus on things like color and appearance. Use descriptive terms very literally and avoid interpretations. For example, use the term, clear, or transparent, not water-white. Use adjectives to describe qualitatively the degree of intensity of the color or cloudiness.
For example, if describing how cloudy a solution became, state what diameter beaker may occlude normal font print on a paper behind the beaker from being readable. Use a scientific dictionary together with a thesaurus if necessary, to expand your vocabulary with a more exact description. You may, on the other hand, find that the solution, that was originally clear and colorless, immediately became opaque and uniform and was light blue in color when the reagent was added. State this, instead of just saying a blue solution resulted.
6. Quantitative Observations and Results, (Data)
Record all measurements and the name and model of the instruments used to record them. Remember not to drop zeroes when such are able to be measured my the instrument. For example, if your balance reads 2.100 grams, then enter 2.100 not 2.1.
Weigh samples by difference. Do not use the tare weigh; especially in a shared lab when you are weighing various materials for various purposes. Always weigh your container after zeroing the balance. Report the weights with the sample and without the sample to obtain the exact sample weight used. When possible weigh the substance to be used in the vessel you intend to use. Record all weights that were taken not just the difference. Make sure each weight is distinguishable and labeled accurately in your report. See example below.
Paste originals or photocopies of all instrumental print outs and state what instrument name, model, and condition used.
Use a subsection to report results. Distinguish measured results clearly from calculated values derived from use of the measured value in an equation. Show the equation used.
If reporting on three or more materials, use a table with rows and column for each material, and the result of each measured or calculated value for each.
If reporting the same calculation carried out on may individual samples, you may just report results of the calculation done on one sample or trial including the details of the calculation. Reference all the values in the table for which the same calculation was used. You may even use Excel or similar tools for such purpose, but details for the equation must be reported.
Other calculations that are expected are details of percent yield or percent recovery. When you have a crude (wet) measure before drying, report it as such, and clearly distinguish it for weights after drying. If you perform a recrystallization or sublimation, report the weight before and after. Record when each weight was measured. For example, sometimes samples may be left to air dry between one lab day and the next. It is important to state how long a sample was allowed to dry and how it was dried.
When calculating yield, you may need to determine the limiting reagent. Show the details of these calculations as well.
Graphs may be appropriate in some experiments such as distillations, titrations, and certain types of chromatography or spectroscopy. Be sure to include graphs and spectra.
7. Discussion & Interpretation of Results
This should start with the major interpretation that you were able to make based upon your operations data, and calculations using that data. Avoid making vague general claims and using hyperbole. Make only the specific claims that your data and observations support. Follow each claim or major interpretation with the most relevant observations or data that support the claim. Make the connections between what you observed, data you obtained, and how that supports or does not support the main purposes of the laboratory exercise and the theories is was intended to exemplify or corroborate.
See example below of contrast between hyperbole and specific supportable claims under General Guidance section.
8. End Matter
Include details of reference used throughout the report. Make sure statements in the report include an end-note number that ties each statement to the correct reference used for it. One reference may be used several times in the same lab report.
The instructor may assign test questions. Include these, and answer correctly for full credit.
1.5 General Guidance on Reports
- Avoid "Vague Generalizations" and "Hyperbole".
- Use only specific claims that may be supported by observation and data
For example, statements like , "This experiment went very well" or " I accomplished all that was intended in this experiment" are of little value, and you may lose more points for saying so if your data obviously does not support such a value judgement or claim. Your lab report is not intended to be an advertisement or an example of expository writing.
It is appropriate, (if data support it), to say, for example, "The melting points observed for all four substances I measured, after recrystallization and drying, were well within the range as reported in the literature for each substance. This indicates a lack of impurities."
Next, follow up and elaborate or qualify your claims where appropriate. Make sure you immediately identify the data or observations to support the specific claim. You do not want to repeat everything that was in your qualitative and quantitative results, but you do want to highlight and repeat specific data or observations that most directly support your claim.
For example, instead of saying, "I learned that some substances were more difficult to recrystallize than others", state which substances were more difficult, what you specifically found difficult, and why this may be so, or what you did because of the difficulty.
As another example, if true, you should report that the melting points for all four substances measured after recrystallization and drying overnight in the fume hood were all well within the range as reported in the literature for each substance. This indicates the products were of a purity desired, indicating the purpose of the recrystallization was achieved. Then show a table with the data for each substance to back up your claim.
When reporting yield in the quantitative results section include details.
Make sure you did not confuse theoretical (maximum calculated ) yield based upon stoichiometry limits of excess reagent vs. the limiting reagent yield. As you recall, many reactions are limited by equilibrium. The text may tell you the equilibrium yield. Be clear which you used to compare your result.
In the discussion, state what observations support where you may have lost yield and what you may reasonably do next time with same or similar equipment to improve yield. Start with minor modifications that likely will have the biggest impact.
When you make a claim in the discussion like, "The product I obtained was that expected from a E2 mechanism." include details.
State what properties of your product indicate it is or is not the product of an expected mechanism (ex. Sn1, Sn2, E1 or E2 mechanism). State any product that may be reasonably forming from a competing mechanism. For example, you will learn sometime a both a Sn2 and E2 mechanism, although the product of one mechanism should be formed in greater amount than the product from the other mechanism. Look to observations of yield and purity (e.g., thin layer chromatography, mo, IR, HNMR) for the evidence.
Many students think their instructor wants to see lots of positive claims. Try making at least two valid claims about what went as expected and make sure to discuss unexpected results and what may have caused them. The instructor only wants to see claims supported by your observations and data.
Your ability to state accurately whether the data supports or (seemingly) contradicts the theories you investigated in the experiment, is an important skill to develop and demonstrate.
Instructors do like to hear what you learned uniquely in the lab. But, don’t go out on a limb to just be able to include such a claim. The claims should come out of the observation, data, and your rational analysis and interpretations and not be compelled solely by the stated purpose of the lab.
Which of the following are examples of undesirable hyperbole and vague claims that should not be used in lab reports?
The results were all exceptionally accurate.
This experiment taught me all I needed to know about safety.
I totally screwed up this experiment.
My final dried sample of recrystallized benzoic acid indicates it is of an acceptable purity because I observed that the melting point of the sample was contained within the melting range reported by PubChem for a relatively pure benzoic acid sample.
1.6 Additional Information
Throughout this laboratory course and other organic chemistry courses, the structure of molecules and what happens to certain atoms and bonds in particular as a chemical reaction proceeds (mechanisms) are discussed as if we can see atoms. The instrumentation used in our lab does not allow us to view molecules and mechanisms, but we have lots of supporting evidence from spectroscopy and other tools that support the various ways we draw molecules or build computer assisted visualizations.
The video below is intended to help you understand some of the tools used for capturing the image of something as small as an atom and watching things happen on the time scale of individual atomic or molecular events measured in femtoseconds, ( 10-15 seconds).
The Elemmeyer flasks above remain among contemporary iconic images of chemistry lab glassware. Make sure you are familiar with the glassware we will use in this lab. A convenient list and image of common organic lab glassware can be found at the following:
 Table created by author using Microsoft Word.