Learning Objectives
• Be able to properly identify the sections included in a scientific paper and a formal lab report.
• Be able to set identify the differences between the Discussion and Conclusion sections of a formal lab report.
• Recognize the difference between a lab manual and a lab notebook.
• Know what is expected of you before, during, and after each laboratory section.
• Set up your Mastering Chemistry account.
• Given an example conclusion from a formal lab report, be able to properly identify, and correctly rewrite it into a satisfactory conclusion.
• Familiarize yourself with the policies and procedures of the laboratory.
Why Write Lab Reports?
A formal laboratory report allows a chemist to share the information they discovered in the lab with other scientists. Scientific work of any sort is useless unless it can be clearly communicated to others in the field. A laboratory report is a concise way to present the relevant results from the experimental observations obtained in each laboratory section. Each and every equation recorded in the pages of your textbook is the result of observations in the laboratory. Your formal laboratory report will allow you to verify and discuss your individual results and validate the relationships discussed in class and in the text. A properly crafted lab report will convince the reader you have adequate knowledge of the subject matter you are analyzing in the lab.
Formal Lab Report Guidelines
A formal laboratory report or scientific paper should communicate the most important aspects of a chemical experiment, containing sufficient detail to reproduce the work and a critical analysis of the effectiveness of the procedure. At the same time, it should be clear, concise, and parsimonious, saying all that is necessary in as few sentences as possible. These guidelines will better prepare you for the writing you will use in your labs, courses, and future jobs.
The Journal of the American Chemical Society provides a list of guidelines for each manuscript submitted for publication. Each journal article generally includes the following:
• Title
• Author Name
• Submission Date
• Abstract
• Introduction
• Experimental Details
• Results and Discussion
• Conclusion
To illustrate each section of a journal article I will use the following article: J. Phys. Chem. B, Vol. 109, No. 1, 2005, in which Dr. Goldberger is the first author. Selected portions of the article are reproduced with permission from J. Phys. Chem. B, Vol. 109, No. 1 ©2005. American Chemical Society.
Title, Author Name, and Submission Date: These items should be placed in the upper left hand side of the first page of your lab report. You must also include your TA’s name. A cover page is not necessary and should not be included in a formal lab report.
Abstract: An abstract briefly states the problem or purpose of the research, indicates the experimental plan used, summarizes the principle finding, and points out major conclusions. The optimal length is one paragraph. Note the abstract shown below is very brief and lists only the most important details. Many journals limit the word count of
an abstract to be 200 words or less. The only abstract you will be required to write this quarter will be for the Solar Cell lab. Instead, you will need to include a Purpose for each formal lab report.
Purpose:
Rather than include an abstract for each report, you will be required to write a purpose statement. In ONE OR TWO SENTENCES describe the purpose of the laboratory experiment. Do not use phrases such as “The purpose of this lab is…” or “Today we performed an experiment to determine the Ksp of…” Make a statement that does not begin with unnecessary prefaces and that instead directly states the purpose without wordy introductions or opinions. This statement should be brief and concise. Site an appropriate reference if needed.
During each lab period, please ask your TA or Peer Mentor to check your purpose statement written in your lab notebook and verify that it is acceptable before you leave class.
Introduction: This section is often referred to as the “Background” section stating the theory behind the experiment. In the context of this class, the “Introduction” section is contained in the introduction section of the lab manual and will not be included in the formal lab report.
Experimental Details: Also known as the “Procedure” section, these details will be recorded in the “Narrative” section in your lab notebook. A proper narrative should be written in the past tense. While you’re in the lab performing each experiment you will need to keep a narrative. A narrative simply indicates what you did in the lab, in the past tense, and must list any observations/results you obtained. Here are the first five steps of the Ksp procedure:
1. To prepare the saturated solution of Ca(IO3)2 measure roughly 20 mL of 1 M Ca(NO3)2 into a 250-mL beaker. Next add about 50 mL of 0.2 M KIO3 to the Ca(NO3)2 solution. You should observe a white precipitate. Note: These volume measurements do not need to be exact, so you can use a graduated cylinder to add the solutions to the beaker.
2. Similar to Figure 2, assemble a ring, clay triangle, and funel with filter in order to perform a gravity filtration. Fold a piece of filter paper in half, then fold it in half again. In order to fit the filter paper snugly inside the funnel, tear off a small part of the corner as shown in Figure 1. Open the filter paper so that one side of the funnel is in contact with a single layer of the filter paper and the other side of the funnel is in contact with three layers of the filter paper.It seems to work best if the side with the tear has three layers. The paper should be in smooth contact with the funnel at the top, but not near the point. Squirting in water with a wash bottle sometimes helps to keep the filter paper in place.
3. Take the 250-mL beaker from Step 1 and pour as much supernatant liquid through the filter paper as possible, trying your best not to disturb the precipitate. Use a wash bottle filled with distilled water to wash down the sides of the beaker. Swirl the wash water with the solid and quickly pour the mixture on the filter paper. Rinse any remaining solid onto the filter paper with a small amount of water from your wash bottle.
4. Wash the solid Ca(IO3)2 on the filter paper with three small portions of distilled water.
5. Using a microspatula, transfer roughly 1/3 of the wet precipitate to one 100-mL beaker. Leave the left over precipitate on the filter paper. You will only use the precipitate on the filter paper if you mess up one of your trials.
A narrative for those steps would look something like this:
1. A saturated Ca(IO3)2 solution was prepared by combining 20 mL of 1 M Ca(NO3)2 with 50 mL of 0.2 M KIO3. A white precipitate was observed.
2. A gravity filtration was performed to isolate the solid obtained in step 1.
3. The white solid was washed three times.
4. Roughly 1/3 of the precipitate was transferred to a 100-mL beaker and 80 mL of distilled water was added.
5. A stir bar and motor were obtained and were allowed to stir for 20 mintues to achieve a saturated solution of Ca(IO3)2.
The narrative basically highlights the key points of what you did and indicates any results. It does not include any unneeded details, such as how to fold the filter paper properly. Those are written for you, as a general chemistry student, so you can reproduce the procedure properly. The narrative, and lab reports, are written for a more experienced chemist. After Lab you will need to take the step by step Narrative section from your lab notebook and put it into paragraph form, creating the Experimental Section of your formal lab report.
Note that this section focuses on the experiment and not the experimenter. There is no use of I, we, or any personal pronouns. This is simply a procedure, in a condensed manner, written in paragraph form. These Experimental Details will allow an experienced chemist to reproduce the experiment.
Results and Discussion: The “Results” portion of this section can simply reference your attached Report Sheet. You must also attach sample calculations (These calculations can be written out neatly and do not need to be typed).
The “Discussion” portion is the most difficult section of the lab report to write and you will be given three to four critical thinking questions to answer based on your experimental results collected in the lab. This section must be written in full sentences and it should convince your TA you know the concepts covered in the experiment. The discussion section allows a chemist to discuss their results, while a conclusion section simply lists them. In this section you can compare your results to literature results and discuss any error. It is not adequate in your formal lab report to attribute the error of your experiment to “human error” or “instrumental error.”
When necessary, this section contains any figures, plots, graphs, or tables.
The Results and Discussion section is the meat and potatoes of the lab report. In Dr. Goldberger’s paper, the Results and Discussion section accounts for 4 of the 5 and a half pages. Note: this does not mean your “Results and Discussion” section should be 4 pages long. The experimental results collected from his experiment were the result of a year’s worth of work. Your Discussion portion of the formal lab report should be as short as you can make it, but it must also effectively address the critical thinking questions given to you by your TA.
Conclusion: Before the details of the Conclusion section are discussed, take a look at Dr. Goldberger’s conclusion to a five page journal article.
This conclusion is four sentences long. I’ve seen students from chemistry 121 write conclusions longer than this one for their lab reports. The biggest misconception students seem to have about lab reports stems from the difference between a discussion and a conclusion section. The Results and Discussion Section of the lab report can be lengthy, but the conclusion should be very brief.
A good conclusion for most general chemistry lab reports should be no longer than four statements. These statements should include the following:
Statement #1: Restate the purpose in the past tense.
Statement #2: Report the relevant results in sentence form.
Statement #3: Discuss any error(s) associated with the lab.
Statement #4: Conclude the experiment and summarize how the lab is consistent with topics from the lecture/textbook.
You should never include your opinion in scientific writing. State the facts and how they are relevant. Avoid using personal pronouns, such as ‘I’, and never use phrases such as “I learned a lot today,” “This was a great lab,” or “Today we performed a thermodynamics lab and showed how a titration related to thermodynamic data.”
Never start the conclusion or discussion with “In this lab…”, “In this experiment…”, etc.
The following statements demonstrate good versus bad statements:
Good Statement #1: The solubility product constant for calcium iodate was determined by titration of the iodate ion in a saturated solution.
Bad Statement #1: I determined the Ksp of calcium iodate via titration using a 10.00 mL pipet and a buret to calculate the iodate ion concentration with a buret filled with S2O32– in order to calculate the end point when the solution turned from blue to clear.
Remember that when you are writing a lab report, you are writing it to an experienced scientist. They know what a titration is and you do not need to explain the minute details. Never use the word ‘I’ in your conclusions.
Good Statement #2: A saturated solution of calcium iodate was prepared and the equilibrium concentration of IO3–(aq) was determined to be 0.0024 M. Stoichiometric relationships yielded a Ksp of 7.8 x 10–7 +/– 4.3 x 10–8 for Ca(IO3)2 at 25˚C.
Bad Statement #2: I determined the iodate concentration to be 0.0024 M by performing three different titrations. This allowed me to make an ICE table and use 4×3 to calculate the Ksp of Ca(IO3)2 to be 7.8 x 10–7.
Be sure to list all relevant information. The Ksp of a slightly soluble salt is highly dependant upon the temperature, so that value must be included in this section. What is not needed in the conclusion section is how the calculations were performed. There is no need to mention an ICE table or 4×3. Those details should be included in the calculations section. If more than one trial is performed then the associated error must be included. The Ksp is an experimentally determined number and it must have +/– error in order to be a scientifically reported value.
Good Statement #3: According to the CRC Handbook of Chemistry and Physics, the literature value for the Ksp of calcium iodate is 6.4 x 10–7 at 25˚C[1]. The experimentally determined value of 7.8 x 10–7, also at 25 ˚C, indicated that the end point of the titration was overshot, thus leading to a larger experimental solubility product constant.
Bad Statement #3: I think I may have overshot the endpoint of the titration, which is the most likely cause for error in this experiment. The reported value of 7.8 x 10–7 is inconsistent with my results, but my TA says that Ksp values are very hard to determine, so I am OK with those results. If I had to do this experiment over again I would be less careless and more careful at the endpoint of the titration.
The error analysis/discussion part of the lab report is not a confession of your opinion or your performance. If you are going to report a literature value you must cite the source and list it at the bottom of the page, as shown below. Do not state what you would do differently if you had the opportunity to redo the experiment. Never use phrases such as “I think…” You were the one who performed the experiment so anything you write is a statement of what happened. If you are taking proper observations in your notebook, you will be able to identify and report your error(s) accordingly.
Good Statement #4: The results from this experiment illustrated how titration data, accompanied by the proper stoichiometric relationships from the equilibrium established by a slightly soluble salt in aqueous solution, can be used to calculate its solubility product constant.
Bad Statement #4: In class we have been studying solubility. We showed that one of the ways to calculate and equilibrium constant is by using a titration to calculate the moles of S2O32– in solution, then to convert them to moles of IO3– in solution and calculate the Ksp. This is one way the solubility tables in our textbook are generated.
[1]H.P.R. Frederikse, David R. Lide, ed. “Solubility Product Constants”, in CRC Handbook of Chemistry and Physics (89th ed.). CRC Press/Taylor and Francis, Boca Raton, FL.. pp. 8–118.
Note: The most common misconception students enter Chemistry 123 with is the difference between a Discussion and a Conclusion. Re-read those sections above and discuss with your TA or peer mentor the appropriate material that should be included in the Discussion and Conclusion sections of a formal lab report.
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