Lab Report Writing

A lab report is a technical means of telling a story. It should be constructed so that you tell the reader: the theory you are testing, how you are testing it, the results you obtained and a discussion of their significance. The sections below will help you to effectively demonstrate your understanding of the lab and the related theory.

1. Cover page. Contains: experiment title, your name, class name and block, and date of lab. A picture or graphic or drawing may be used but is not required.
2. Introduction. Gives basic scientific theory or background information about the experiment. Explains how a theory is being put to use or tested in the lab. This section is very important as it is here that you are best able to demonstrate that you understand the scientific background of the lab. Be careful not to simply paraphrase the background information given in the lab handout! Use your own words. Also, make a connection between what you did and what you measured in the lab and the scientific background information.
3. Procedure. Summarizes what was done during the lab. Written in first person, past tense, active voice. The level of detail should not be excessive but should be sufficient for the reader to repeat your experiments exactly. Tell what you actually did—do not paraphrase the lab handout. Include your observations from the lab in this section so that someone repeating your procedure will know if they are on the right track. Your observations are absolutely essential. This section may run from 3 - 5 paragraphs.
4. Data and graphs. The data section briefly presents the data that was collected. Raw data sheets written during the lab are never presented as part of the formal lab write-up. Construct a neat and well thought-out table to most effectively show your results. Tables should be numbered and titled below the table.
   
   If the lab requires it, you will create informative graphs to enhance your discussion of the results. Graphs should be numbered and titled as figures (Figure 1, Figure 2, etc). You must discuss the meaning or significance of the graph in the analysis section. Do not include a graph and fail to mention it in your text. Refer to graphs by number.
5. Sample Calculations. The sample calculation should include the equation with variables first, then with numbers and units substituted for the variables and finally the final result. Equations should be numbered and referenced in your analysis section. Note: you may have used the equation many times, but you only have to show it once.
6. Analysis. The most important section of a lab report. This is where you specifically answer the objective questions. Report numerical results with plus-or-minus amounts and percent error. Discuss physical reasons for the size of your error: come up with a scenario and work out its consequences. If your data were highly variable (that is, imprecise) then discuss physical reasons for this. Try to account for the size and direction of any inaccuracy if you have a standard for comparison. Explain the relationship between your results (refer to data tables by title and number) and the answers to the questions posed in the lab handout. The Analysis will frequently have several parts as you answer some questions that were provided with the lab handout. All answers must be in paragraph form as in an essay. Do not number answers to questions!
   
   Scientific explanations usually consist of a claim (also called a hypothesis), evidence for the claim (collected during the lab activity), and the reasoning that connects the two.
   Here is an example of writing that fulfills the above description:
   

   “I know the candle burns vaporized wax because of four key observations. First, the flame moves in the air the way a gas would, flickering and reacting to air currents. Second, the flame dies down after the candle is first lit but grows again after the wax melts. Third, I can collect liquid wax on a watch glass placed in the clear bottom part of the flame. This shows that the wax must have vaporized because the glass never touched the melted wax at the top of the candle but collected wax on it simply by being in the lower part of the flame. Finally, when the candle is extinguished the smoke is flammable and allows the candle to be lit by a flame placed in the stream of smoke. This shows that vaporized wax is the fuel in a candle flame because the stream of smoke, being flammable, must be the material which was feeding the flame until it went out.”

7. Conclusions. This section describes the overall success of the experiments. Discusses whether or not the results were expected, whether errors may have occurred or alternative experimental techniques may have been used for better results. Describes how your understanding of the theory has been improved by performing the lab. How does the lab apply to real life? What did you learn? How would you make the lab better? How could the lab be extended?

Make sure your report is neat: typed, stapled or bound, pages are numbered, sections (above) are labeled and in order, no misspellings, no typos, font size 12 pt, margins of 1", 1.5 line spacing. Reports are usually 2 - 4 pages.

Read the lab handout carefully several times and refer to it when you are doing your labs. Typically the lab handout will spell out what you must consider in your analysis. Make sure you address each question.

Write your report for a stranger. Don’t assume your reader knows too much about science or the lab. If your lab is written properly, this type of reader should be able to make sense of what you did during the lab and what you have concluded.

Be concise. This means present all the relevant information as clearly but as briefly as possible. Extra descriptive words are not useful in scientific writing. This is not a class where you are being graded on how many pages you write. Often the worst reports tend to be the longest ones, as a lack of knowledge causes the writer to go on and on in the hope of stumbling on the correct response.

Look at the sample lab reports. Here is one for a lab involving observations of a candle. Here is another about finding the density of a variety of substances.

Common Student Mistakes:

• Some students failed to include their observations with the procedure. The procedure is meant to relate to others how to do the experiment. Your observations will be very helpful in assuring others that they really are replicating your work.
• When writing about your observations do not write that you carefully noted them without writing down what they are!
• Sample calculations must be typed separately from the Analysis section. Do not describe calculations! Just give your results and the interpretation of your results.
• The Analysis section of the report is meant to interpret your lab results. Discuss your observations and explain how they are connected with the conclusions of the report.
• In writing your report be sure to write about what you learned; do not simply state that you learned about something!
• Remember that all instruments used for measurement have an inherent uncertainty. For example, discrepancies in results of 0.5 g or less on the lab balances is probably within the expected variation for the instrument.
• Recognize the difference between errors due to the limitations of equipment and human error.
  • Human error can be eliminated. Learn how to use the equipment properly. Be careful while you work. Follow instructions. If you realize you did something incorrectly, go back and do it correctly. It’s all part of the learning process. Never use the phrase ‘human error’ in a lab report as it is nothing more than a sign of laziness or unwillingness to think about true sources for experimental variation.
  • Equipment error is something you need to be conscious of.Measuring volumes with beakers introduces huge errors in your data: usually ±5%. Volumes measured using a 10 mL graduated cylinder can be precise up to ±0.1 mL. Masses measured using a three-beam balance can be precise up to ±0.2 g. Temperatures can be precise to the tenth of a degree. Lengths measured using a millimeter ruler can be precise to ±0.1 mm.
• When giving background information do not simply paraphrase (parrot-phrase) what I wrote or what I said in class; figure it out for yourself and put it in your own words