Appendix 9: How to Write a Conclusion
The reason to write a conclusion is because your lab report might be long and the reader may not remember
all the important points. Also, it gives you a chance to explain anything that might have gone wrong or could
be improved.
A useful way to get started is to write an outline like you did for your English composition classes. Then turn
the outline into full sentences, with proper punctuation and grammar. Summarize your major findings. This
section should be complete so that the reader has a clear understanding of the goals, results, and conclusions
without being redundant to the previous sections. Show that you really understood what you did in the lab,
instead of simply filling in numbers.
Keep in mind that you are writing about what you did, so write in past tense. Traditionally, first person is
avoided in order to appear less biased, so write in third-person, passive voice (English composition
professors, eat your heart out!). For example, instead of ‘We mixed two solutions of different densities,’ write
‘Two solutions of different densities were mixed.’
Avoid unsubstantial and subjective comments. Instead of ‘I had a lot of fun’, describe what you learned.
Instead of ‘a lot of crystals were obtained,’ be very specific: 0.876 g of white, needle-like crystals were
obtained.
Try the following structure.
o First paragraph:
o Re-state your purpose or hypothesis.
o What concept were you investigating? Describe how it related to the experimental procedure.
o How did you go about your work and why? This is not the details of your procedure repeated, but
discussion of the processes. For example, describe the methods that you chose for finding volume
of specific shapes of unknown objects.
o Second paragraph:
o Summarize your final results (not any intermediate results). Then answer: was the purpose met?
What evidence proves it? What is your conclusion for each part? Use the values you obtain as
evidence in your reasoning. Statements like, "see data table for values" are not acceptable!
o Discuss the validity and reliability of your data in answering the question. Are the results
reasonable? How do you know? For example, if you obtained a density of 4 g/mL for a plastic,
that would not be reasonable since typical plastics vary from 0.7 – 2.2 g/mL per the data table in
the experiment. If you obtained unreasonable results, what were the expected results? Explain
based upon what you know from lecture and the lab manual.
o If you calculated a standard deviation, report it right after the mean it is associated to with + in
between. If a relative percent error was calculated, follow the above with it. Example: The density
of unknown 4 was 1.8 g/mL + 0.3 g/mL. The relative percent error of this density was 2.5 %.
o Third paragraph:
o Discuss any problems during the experiment and any errors. These should be more than errors
within your control such as ‘the glassware must have been dirty.’