Laboratory Reference Manual, Chemistry 201/202
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How to Write Lab Reports
SECTION DESCRIPTIONS | EXPERIMENTAL | COMMON ERRORS

You are expected to write a lab report for each experiment that you perform in Chem 201/202. Generally speaking, these reports are separate documents from your lab notebook. Each report will be evaluated on its own merits as a technical document, i.e., as a useful and complete description of your scientific work.

This page offers general instructions for writing lab reports. Read it carefully. Your report will be evaluated partly on how well you follow the instructions given here. (FYI - Since you will only write a few reports and they will be separated by several weeks, you should probably review these instructions each time you write a report.) Some experiments also give additional "local instructions" for writing lab reports. Local instructions always take precedence over general instructions.

For an example of local instructions, sample lab reports are provided for three Chem 201 experiments. Instructions on how to use these samples are provided with the first sample report (Synthesis of Salicylic Acid).

Evaluation. Lab reports will be evaluated using the following criteria:

 
  • Effectiveness as a scientific document. Are procedures and observations communicated clearly and completely? Are figures properly labeled? Are literature publications cited adequately? Have spectra, etc., been attached to the report and are they properly labeled?

  • Scientific content. Are conclusions and interpretations scientifically sound? Have calculations been performed correctly?

  • Adherence to the rules of good writing. Does the author use good grammar, spelling, word usage? Are technical terms used appropriately?


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Descriptions of Report Sections

A complete report contains the following items:

 
  • Title

  • Abstract

  • Results and Discussion

  • Experimental

  • References

  • E-factor

  • Supporting documents (usually spectra)

This list follows the same pattern used to write articles for organic chemistry research journals (we have omitted one section that every article must contain, the Introduction, and added one section that no articles currently contain, the explanation and calculation of E-factor). We encourage you to look at some articles in the Journal of Organic Chemistry as a way of learning how to write satisfactory reports.

Instructions for each report section are provided below (additional instructions specifically designed for formatting your Experimental section are provided in the next section). Our instructions are a simplified version of the Guidelines for Authors that the Journal of Organic Chemistry publishes online.

Title. The report's title should clearly and accurately tell the reader what the report is about. Choose title terms that are as specific as the content and emphasis of the report permit; for example, "the synthesis of benzoic acid from bromobenzene and carbon dioxide" is better than "the synthesis of a carboxylic acid".

Balance brevity against descriptive accuracy and completeness. A two- or three-word title may be too cryptic. On the other hand a 14- or 15-word title is probably unnecessarily long. Ideally, a title should be an ultra-brief abstract. [BACK TO TOP]

Abstract. An informative abstract summarizes the principal findings of the report in a single paragraph (usually 2-6 sentences). The ideal abstract will briefly indicate the experimental plan used in the research, summarize the principal findings, and point out major conclusions. Most readers read the abstract first (or right after they read the title). Most authors, however, write the abstract last to make sure that it reflects accurately the content of the report.

Keep in mind the purpose of the abstract. It helps the reader determine what kind of information is contained in the report. The abstract is not a substitute for the report itself.

The abstract should be self-contained. It is not unusual for an abstract to contain a graphical image that captures the most essential feature of the report. However, an abstract should not refer to numbered tables, figures, or references located in the body of the report. Compounds should be identified by name, or by an unambiguous condensed formula or abbreviation. [BACK TO TOP]

Results and Discussion. Some research articles contain separate Results and Discussion sections, while other articles combine these sections. The following instructions describe each section separately, but you should always combine these sections in your Chem 201/202 reports (your experiments are so short, they do not provide enough material to justify separate sections).

Results. This section is the heart of your report. All experiments and results of significance should be described here. Use your judgment; a melting point might be the central finding of one experiment, but might be trivial information in another.

The Results section should answer questions like these: How did you prepare your compound? How did you isolate it? What were its properties: mp, bp, spectroscopic, chromatographic, etc.? How did you establish the compound's structure? Virtually all data tables, graphs, spectra, etc., appear in this section.

As a rule, do not give the details of your experimental procedure here. This information belongs in the Experimental section.

Many experiments can be summarized by following a three-step sequence: describe what you did, describe what you observed, then interpret your observations. This sequence naturally draws the reader through a train of logic that makes conclusions more compelling.

Since most of the experiments in this course involve only one or two procedures, your Results sections will always be quite short. [BACK TO TOP]

Discussion. This section is reserved for interpretations of observations reported in the Results. If an experiment has a simple interpretation, this section may not be needed. On the other hand, if the results of several experiments must be assembled into a single coherent picture, a Discussion is called for.

You can also use the Discussion to compare your procedure to other, previously published procedures. Or, you might compare your observations to other published descriptions of the same phenomenon.

Keep your Discussion short. Unwarranted, unsupported, and vague speculations should be avoided. It is unreasonable to write, "The successful synthesis of compound X probably means that other compounds can be synthesized." This adds nothing to the reader's appreciation or understanding of your work.

Here is another example of something to avoid, "Errors in temperature readings may have been due to a poorly built thermometer." This author is grasping at straws instead of describing relevant experiments and observations. A "poorly built thermometer" is an assertion that can be tested scientifically. The author should either perform the test and describe its results, or just keep quiet. [BACK TO TOP]

Experimental. This section contains a complete description of your procedure. Enough detail should be given in this section so that any trained chemist can repeat your procedure and obtain comparable results. Thus,

 
  • All compounds and amounts must be identified. Purity and concentration of reagents should also be reported where relevant.

  • Apparatus should be described only if not standard. Commercially available instruments need not be described.

  • All procedures should be described. Details of the procedure should only be provided if the procedure is not standard. For example, "crystallization" is a standard procedure. However, the word "crystallization" does not specify the solvent and temperature used, so these details must be included in order to provide a complete description.

  • All quantities, measurements, and observations of significance must be included. Most Chem 201/202 experiments involve the preparation and purification of a compound. You should include all of the observations you used to determine the amount, purity, and identity of your compound. These observations include, but are not limited to: mp, bp, yield (actual mass and %theoretical), and important spectral features along with their assignment.

References. Data never appears out of thin air. If your report contains data, facts, or theories that you did not generate yourself, then you must list your sources in the References section.

The References is not a bibliography. Do not simply list the books and articles you consulted. Every item listed in the References must be cited somewhere in your report. Or, turning this around, every time you mention a 'fact' that you obtained from another source, you should put a number next to this item (put the number inside square brackets as in [1]) and list this source with the same number in the References section. Here are standard formats for citing sources:

 

Book

1. Author(s), "Title", Publisher, City, Year

 

Research article

2. Author(s), Journal, Year, Volume, Page

 

Web

3. URL

 

Human

4. Name, Personal communication

Do not include references for items that are considered general knowledge. Some judgment is required here, but 'general knowledge' seems to include things like atomic masses, basic principles of chemistry (for example, acids react with bases), and so on.

Finally, never refer to this manual as a reference. Any numbers provided in this manual (mp, bp, d, etc.) should be obtained from a more reliable source (CRC Handbook, Aldrich chemical catalog, etc.). [BACK TO TOP]

E-factor. The E-factor, and the method for calculating it, are described in the Calculations appendix. This section should list the items that were considered in calculating the E-factor and can be written as a simple list, "This experiment used the following materials: sulfuric acid (3 g), NaOH (10 g), ... ", followed by the necessary calculations. [BACK TO TOP]

Supporting documents. Supporting documents are of two types. First, there are spectra and chromatograms that you measure in the lab. These should be labeled as figures and attached to your report. Second, there are figures and data tables that you draw in your report. These also need to be labeled.

The proper labeling for a figure (or table) goes like this, "Figure x. short caption describing content", where x is a number.

You must attach original copies of all spectra (NMR, IR, GC-MS) to your reports. Take good care of these spectra. Immediately label them with your name, course, lab day, and sample, and store them in a safe place (do not just fold them inside your notebook).

Some reports also ask for information about thin-layer chromatograms (TLC). Do not attach the original TLC plates to your report. Instead, make a full-scale drawing of your plate showing the observations that you recorded in your notebook. [BACK TO TOP]


Formatting your Experimental section

The Experimental section is the hardest one to get right, especially when you have spectroscopic data to report. Procedural language obeys strict conventions and is compact to the point of being dense. At the same time, it is filled with strange technical terms and contains many embedded calculated quantities. A well-written Experimental section can be the most valuable part of any report or article because it provides a complete recipe for any other chemist who wants to attempt the experiment.

This section describes some of the conventions used to format the Experimental. We begin with an example drawn from a recently published research paper:

published experiment sample

Despite the grammatical and typographical errors (the authors are not native speakers of English), this is an effective description of an experiment, and it illustrates how chemists can make themselves understood across international borders.

The sample does not follow our formatting rules exactly (please refer to the rules given below when preparing your Experimental), but it is still instructive. Notice that the experiment is described using three components: title (bold font), procedure, and observations. The observations appear in two places. Those made during the experiment are incorporated into the procedure (for example, "orange solution" and "yellow-orange solid"). The remaining observations are measurements made on the isolated product and are placed after the procedure.

Also, notice that at least half of the experimental description refers to measurements made on the isolated product. These measurements always begin with the amount of compound obtained (1.4 g) and the theoretical yield (93% taking Pd as the limiting reagent). These authors chose to follow this information with the results of a C, H, N elemental analysis (the observed "Found" values are in good agreement with the expected "Calcd" values). The rest of the paragraph describes important peaks in the infrared (IR) spectrum, peaks in the proton (1H) NMR spectrum, and peaks in the carbon (13C-{1H}) NMR spectrum.

You should follow the same general principles as this example when formatting your Experimental sections, but please follow the detailed formatting instructions given below.

Each experiment should contain a title (in bold font), followed by a detailed procedure and observations. The initial observations should consist of melting or boiling temperatures, followed by amount of product and %theoretical yield. Spectroscopic observations, when available, come last.

The sample lab reports will help you learn the language of experimental procedures. However, it is quite common for students to have problems reporting quantitative measurements inside the procedure. Here are some useful guidelines:

 
  • If a reagent participates in the reaction, put the amount used in parentheses after the reagent's name. For example, "palladium chloride (507 mg, 2.8 mmol)".

  • Report the amount in one of two ways: either before the solvent name (example: "the solution was combined with 10 mL H2O") or after the solvent name (in parentheses). Do not include the number of moles of solvent.

  • Always report the amount actually measured. If you weighed a compound, report its mass and include appropriate units. If you measured the compound’s volume, report the volume with appropriate units.

  • Always follow the amount of compound with the number of moles (mol) or millimoles (mmol). The number of significant figures in this quantity should not exceeed the number of significant figures in your measurement. For example, 507 mg of palladium chloride is a measured quantity containing three significant figures. Therefore, the number of moles should contain no more than three significant figures.

  • Yields are not very reproducible. Round off to the closest 1%.

  • Research articles do not routinely report E-yields, so this sample does not contain one. Instructions calculating E-yields will be provided in class.

  • Melting and boiling temperatures should be reported to the closest 0.5 oC.

Format your spectroscopic observations according to the following outline:

 
IR (sample type) cm-1: absorption (intensity, functional group/bond assignment), absorption (intensity, functional group/bond assignment); 1H NMR (solvent, xx MHz) δ: chemical shift (coupling pattern, nH, J = xx Hz, assignment), chemical shift (coupling pattern, nH, J = xx Hz, assignment); GC (or GC-MS) (oven temperature): retention time, m/z = value (relative peak height, fragment assignment), value (relative peak height, fragment assignment).

The items in normal font must appear exactly as shown, but the items in italics must be replaced with appropriate entries as described below (it may be necessary to repeat some of these items in order to describe all of the data; separate repeated items with commas).

Here are two examples of properly formatted observations:

Blah-blah yielded methyl benzoate: 3.0 g (72% from benzoic acid), bp 210-214 oC; IR (neat) cm-1: 1735 (vs, C=O); 1H NMR (CCl4, 60 MHz) δ: 4.3 (s, CH3), 7.1 (m, 3H, meta and para CH), 7.3 (d, 2H, J = 8 Hz, ortho CH). GC-MS: 3.4 min, m/z = 150 (30, M), 122 (40, M-CO), 105 (100, PhCO), 77 (50, Ph).

Blah-blah yielded styrene: 3.0 g (72% from benzaldehyde): 1H NMR (CDCl3, 100 MHz) δ: 7.35 (m, 5H, phenyl), 6.7 (dd, 1H, J = 8, 14 Hz, CH=), 5.75 (d, 1H, J = 14 Hz, =CHHtrans), 5.25 5.75 (d, 1H, J = 8 Hz, =CHHcis). GC (90 oC) : 1.1 (styrene), 1.4 (benzaldehyde) min.

Formatting instructions for each type of spectroscopic measurement are provided separately:

IR

sample type: neat, Nujol, ATR (whichever applies)

absorption: vibration frequency; report this value to the closest cm-1

intensity: s (strong), m (medium), w (weak). v (very) can be used to modify the intensity as in: vs or vw. sh (shoulder) and bd (broad) can also be appropriate as in: bd vs.

assignment: list atoms in functional group responsible for absorption, e.g., C=O or NH2.

Do not list all of the bands in your IR spectrum. List bands that 1) correspond to significant functional groups, and 2) identify your compound's molecular structure. If you list more than one band, list them in order of increasing frequency. [BACK TO TOP]

NMR

solvent: CDCl3, acetone-d6, D2O (whichever applies)

xx MHz: 400 MHz is your only choice at Reed for 1H NMR

chemical shift: report this value to the closest 0.01 ppm

nH: report integrals only if they have been measured; these values are frequently off (from the desired integer) by 10-15% when an FT-NMR instrument is used to measure the integral

coupling pattern: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet). Use 'm' when a pattern is uninterpretable. Write out the names of larger patterns: quintet, sextet, septet, octet.

Multiple couplings result in combination patterns, such as doublet of triplets, or triplet of doublets. Since these patterns are due to several independent spin-spin couplings, you must report a coupling constant (J) for each type of coupling. For example, a doublet of triplets is usually a six-line pattern. The line spacings may look complicated, but they can all be accounted for using two coupling constants; one describes the doublet coupling and the other describes the triplet coupling.

Name combination patterns by giving the name of the strongest coupling (largest J) first. For example, an eight-line pattern with a doublet coupling of 12 Hz and a quartet coupling of 2 Hz should be reported as a "doublet of quartets" and not as a "quartet of doublets". Use the abbreviations given above, and list the coupling constants in order. Thus, the eight-line pattern considered above would be described as "(dq, J = 12, 2 Hz, assignment)".

J = xx Hz: report this value to the closest 0.1 Hz. Include this information only when a pattern displays interpretable coupling. Singlets show no coupling and multiplets are uninterpretable, so "J =" should not be included for them.

assignment: Give a condensed formula fragment that unambiguously defines the hydrogens responsible for the signal. If your compound is CH3-O-CH2CH3 then "CH2" is unambiguous and should be entered in the appropriate location. However, "CH3" does not identify a unique set of hydrogens. The signals created by the two methyl groups should be assigned as "OCH3" and "CH2CH3". Since the latter formula contains two kinds of hydrogens, use special fonts (bold or italic) or underlining to identify the hydrogens that cause the NMR signal. For example, you might write: CH2CH3 or CH2CH3 or CH2CH3 to identify the methyl hydrogens as the source of the NMR signal.

There are cases when convenient fragment formulas cannot be constructed. When this happens, draw your compound, and label each hydrogen in the formula: Ha, Hb, and so on. Use these labels in place of a fragment formula to identify the H responsible for the NMR signal.

You must list all of the signals in your NMR spectrum that are created by your compound. List the peaks in order of increasing chemical shift. Do not list signals created by the NMR solvent (CHCl3, HCl, TMS) or by other impurities, such as chromatographic solvent. [BACK TO TOP]

GC & GC-MS

GC only oven temperature: Give the oven temperature in oC

GC & GC-MS retention time: Give the time that elapsed between the injection of your sample and its emergence from the GC (this value is printed on your GC-MS spectrum). If you can identify several components of the mixture, list the retention time for each.

GC-MS only m/z = value: Give m/z ratio of peak as an integer

GC-MS only relative peak height: The "base" peak is defined as the tallest peak in the spectrum and its height is defined as "100". All other peak heights are necessarily between 0 and 100. Round peak heights to closest integer unless height is less than one.

GC-MS only fragment assignment: The molecular ion is assigned by showing the symbol "M" or "M+". Larger fragment ions are usually assigned according to what has been lost from the molecular ion, e.g., loss of a methyl group would be represented by “M-CH3”. Smaller fragment ions are usually assigned according to what they contain, e.g., an acetyl ion would be "CH3CO".

GC-MS only etc.: Always list peaks in decreasing m/z order, i.e., largest m/z first and smallest m/z last.

Do not list all of the peaks in your GC-MS mass spectrum. List the most intense peaks and list the ones that help you identify your compound (the latter might be very weak). The peak produced by the molecular ion should always be listed if it is observed. [BACK TO TOP]


Common Errors

We read several hundred lab reports every year, and some errors are much more common than others. Here is a list of common errors and some recommendations for producing satisfactory lab reports.

Recommendations

 
  • Be explicit. Assume that your reader is an expert organic chemist who is, nonetheless, unfamiliar with the instructions in your lab manual. Your Results section must provide some description of what you did (and this should precede your observations and conclusions), and your Experimental must contain all of the details needed to repeat your experiment.

  • Follow a natural train of logic. Bad logic puts the conclusions before the observations (and procedure): "This product was not formed by an acid-catalyzed process. No acid was used." Good logic starts with what was done, follows with what was observed, and ends with a conclusion. "An acid-free mixture was used to make the product".

  • Build your arguments on thoughtful comparisons. You have described your experiment and drawn some conclusions, but should the reader accept your conclusions at face value? Are your (limited) observations strong enough to support your conclusions? One way to address these questions is to relate your observations and conclusions to the work of others. Compare your observations to findings in the scientific literature. Compare them to well-accepted scientific theories. Compare your conclusions with each other to see if they are internally consistent.

  • Use a spellchecker. Misspelled terms, especially scientific ones, can lead to a great deal of misunderstanding. You may find it helpful to create your own "user" dictionary of correctly spelled technical terms. Note: we make every effort to spell technical terms correctly in this manual. If you have questions about spelling, look for examples of the word in this manual.

(Very) Common errors

 
  • Inserting an ambiguous "it". Example: "Ethanol was mixed with mineral oil, and it was recovered by vacuum filtration." What does "it" refer to? Ethanol? Mineral oil? The mixture?

  • Starting sentences with numerals.

  • Using imaginary technical terms. "The solution was filtered" is acceptable, but "the solution was filtrated" is not. "Salt was weighed" is acceptable, but "salt was massed" is not.

  • Using units incorrectly in prose. "I poured some mL of water into a beaker" is wrong. It should be "I poured a small volume of water into a beaker".

  • Using units incorrectly in graphs and tables. Incorrect label: "mL distillate". Correct column label: "Volume distillate (mL)".

  • Replacing technical terms with long, imprecise expressions. For example, use "distillate" instead of "the liquid that condensed from the vapor at the top of the column".

  • Run on sentences and paragraphs. A sentence describes a single thought and must satisfy the rules of grammar. A paragraph addresses a single topic and often contains a topic sentence.

  • Connecting the data points on a graph.

  • Leaving some NMR signals out of the Experimental, or leaving out required data elements for these signals. All NMR peaks created by your compound must be listed and all required data elements must be included (see above). If you have questions about what is required, please see your instructor.

  • Rounding off too early in a calculation. You should carry insignificant figures through all of your calculations, and round off at the end. If you round off too soon, you may end up with a significant error.

  • Calculating %theoretical yield incorrectly. Yields are based on moles, not grams.

  • Calculating #moles reagent incorrectly. Use molecular weights to convert mass to #moles. Use density to convert volume to mass.

  • Reporting impossibly precise measurements. For example, our graduated cylinders have markings for every 0.1 mL, but it is not unusual for a student to report using "2.73 mL" of liquid. It is impossible for the student to measure the liquid's volume to the nearest 0.01 mL with our equipment.

  • Failing to substitute your observations and literature sources for the ones in the sample reports.

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