How to Write Lab Reports

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, “synthesis of benzoic acid from bromobenzene and carbon dioxide” is better than “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. The fact that the title and abstract convey the same information, but with different levels of detail, is a defining theme of journal articles and lab reports. There is a lot of repetition. The title, abstract, results & discussion, and experimental sections ALL convey the SAME information, but with varying levels of detail.

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 process an article in the order: title, then abstract, then article. The title is essentially an advertisement for the abstract, and the abstract is, in turn, an advertisement for the article. The abstract is not a substitute for the article.

The abstract should be self-contained. 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. After online publication became routine in the late 1990’s, many journals began requiring a graphical image for the abstract. Prior to that, abstracts almost never allowed images.

Some research articles contain a Results section and a separate Discussion section, but other articles combine these into a single Results and Discussion section. The decision is usually subject to the whim of the author. These sections will always be combined in your Chem 201/202 reports (your experiments are so short, they do not provide enough material to justify separate sections), but the contents of each section are described separately below.

Results. This section is the heart of your report. It tells the “story” of your work. This means all experiments and results of significance should be described in the Results section. Because most of the experiments in this course involve only one or two procedures, your Results sections will always be quite short.

The key details for your reports are the ones that answer questions like: 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?

While it is reasonable to mention an experimental technique like ‘reflux’ or ‘recrystallization,’ it is not appropriate to give the details of your experimental procedure here. You might write, “Compound A was obtained by refluxing B with C,” but you would never write, “Compound A was obtained by placing B (3 g, 0.15 mole) and C (2 mL, 0.16 mole) in a round-bottom flask and refluxing the mixture for 30 minutes …”. This kind of detail belongs in the Experimental section, not the Results section.

A good way to think about the structure of your Results section is to view it as a three-part story: 1) describe what you did, 2) describe what you observed, 3) and then finally, interpret your observations. This sequence naturally draws the reader through a train of logic that makes the final conclusion more compelling because the reader can see the work that led up to it. A very common rookie mistake is to put the conclusion first and then follow it with the operations and data.

Discussion. This section is reserved for interpretations of observations reported in the Results. If an experiment has a simple interpretation, this section may not even 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. Likewise, if the conclusions reached in the Results section contradict, extend, or tie together results obtained by other scientists, a Discussion section is needed to integrate the newest findings with whatever had come before.

The most common admonition from journal editors to prospective authors is to keep the 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 like X can be synthesized.” This adds nothing to the reader’s appreciation or understanding of your work.

Here is a particularly common example of the wrong kind of Discussion, “Errors in temperature readings may have been due to a poorly built thermometer.” This is an example of unwarranted speculation. The author should either test their hypothesis by re-doing the experiment with another thermometer or just keep quiet.

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. Since they report detailed procedures and observations, Experimental sections can be long. As a result, many journals have adopted a policy of placing the Experimental section in a separate document that must be downloaded from the internet. If you go to the web page that allows you to download the research article, you will no doubt see additional documents with labels like Supporting Information or Supplemental. The Experimental section is located in one or more of these documents. Within the experimental:

• All compounds and amounts must be identified. Purity and concentration of reagents should also be reported.
• Apparatus should be described only if it is 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 was modified in some way. For example, “recrystallization” is a standard procedure, but this word omits crucial details like the solvent and temperature so these details should be added, e.g., by writing, “crystallization from boiling acetone.”
• 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 % yield), and important spectral features along with their assignment.

If the conclusions in your report rest on previously published data, hypotheses, or theories, that is, material that you did not generate yourself, then you must list these publications in the References section.

Example #1: “The NMR spectrum of compound A contained a signal at 7.9 ppm (2H) that can be assigned to the two hydrogens ortho to the nitro substituent [3].”

Example #2: “The filtrate was fractionally distilled to yield compound A (12.7 g, 37% yield): bp 78-82 ºC (lit.³ bp 81 ºC).”

The sentence in this example contains three parts: a) observations (NMR signals, boiling temperatures), b) interpretations of the observations (the NMR signals are due to ortho hydrogens in compound A, the boiling temperature of the liquid matches that of compound A), and c) literature citations that support the interpretation. It tells the reader that if they want to check on the published document that supports your interpretation, they should go to your References section and look at item #3.

Each citation in your References tells the reader where to find a specific source of information. Your References are not a bibliography. Do not simply list all of the books and articles you consulted in preparing your report. Each item that appears in your References list must also appear as a citation somewhere in your report.

Different scientific fields and publications use different systems for organizing references. Some usebracketed numbers as in Example 1, some use superscripted numbers as in Example 2, and others use first author + publication year (example: “… nitro substituent [Noyori, 1988]”). Chem 201/202 students should use superscripted numbers.

Another source of variety is the format for presenting citations in the References section. Chem 201/202 citation formats should follow these rules based on publication type:

Do not include references for items that are considered general knowledge. Some judgment is required here, but you can assume that ‘general knowledge’ includes things like molecules are made of atoms, atoms have known masses, and other basic principles of chemistry (for example, acids react with bases). You don’t need to find citations for these kinds of things.

Finally, make sure you obtain data from ‘quality’ sources only. These include published peer-reviewed research articles and books, published handbooks such as the CRC Handbook of Chemistry and Physics, and technical specification sheets produced by chemical manufactures such as Sigma-Aldrich, or data aggregators such as ChemSpider.

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.

Supporting documents are of two types: 1) spectra and chromatograms that you measure in the lab, and 2) figures and data tables that are constructed solely to present and explain data in the report. All of these documents, whatever their type, should be provided with captions that describe their contents (the captions should also provide a figure/table number that can be cited in the report).

The proper caption for a figure/table looks like this, “Figure x. short caption describing content“, where x is a number.