Discussion Writing Guidelines:
Grading Rubric: For each experiment there is a grading rubric posted on Gauchospace. Use the grading rubric as a
guide to write your lab report and to write your discussion (use the specific guidelines provided for each experiment).
Paragraph Form: Write your discussion in paragraph form. Be clear, concise and coherent. Start your discussion
with a brief introduction paragraph stating with the purpose/overall goal of the lab and how the objective of the
experiment was accomplished (what method(s) were used and why?). After the introduction paragraph, start a new
paragraph for each part of the experiment and a final paragraph to indicate errors and any final conclusions.
Paragraph: Each paragraph starts on a new line. You start each paragraph with a topic sentence that identifies
the main idea of the paragraph. The topic sentence is followed by the body of the paragraph, which explains the
main idea, using facts, results, arguments, analysis, examples, balanced equations for chemical reactions,
mathematical equations and any other information. You end the paragraph with a concluding sentence that ties
together everything mentioned in the paragraph. A concluding sentence may restate the claim in the topic
sentence, but now it has supporting evidence behind it.
a) Include balanced equations for chemical reactions when the reaction is first mentioned, either in the
introduction paragraph or in the body of a paragraph for a given part of the experiment. Phase designators
such as (s), (g), (l), and (aq) should be used for all products and reactants. Each balanced equation for a
chemical reaction or any mathematical equation should be on a separate line and should be center-aligned
immediately after the reaction is first mentioned. Reactions and equations are placed in the appropriate
sections as they come up in a given section. Use equilibrium arrows (⇄) for equilibrium reactions and a
single arrow (→) for reactions that go to completion. Equations must be properly formatted with subscripts
and/or superscripts. For example, the chemical formula for the ammonium ion should be written as NH4
+
(aq)
instead of NH4+(aq). You can search Google to learn how to use subscripts and superscripts.
b) Experiment: When describing the experiment, explain the general method only – do not write a detailed
procedure. Explain what was measured and explain your results so that the reader understands the experiment
and the results. Do NOT say: “In part 1, the results that were obtained were ….” Instead, clarify what was
measured in “part 1” before you explain the results.
c) When you state your results, explain what they mean! Do not include intermediate values that you
measured; explain the final results that you obtained after completing the calculations. Always compare your
results to the given literature values or what you expected your values to be. Using an appropriate number of
significant figures, state your value, the actual value and the percent error. Reporting the percent error will
indicate how close your results are to the actual value. After you explain your results for each part of the
experiment, indicate possible sources of errors for all results in a final paragraph (see step (d) below).
d) Sources of Error: When you indicate sources of error, look at your results. You must back up any claims
and conclusions with evidence. If your data/results appear to be accurate, provide the evidence that shows
why the results are accurate. If you see a problem in your data/results, explain the errors that you believe
caused the problem in your data. For example: If your value is higher than the known value, explain what
errors in the experiment may have caused your value to be higher and why these errors caused your value to be
higher. Do NOT indicate the error was due to “human error” or due to “calculation errors.” If your
calculations are incorrect you need to do them over. If you did more than one trial in the experiment, indicate
if your results were reproducible or not. If not, explain why not. For a third trial, did two of the three trials
give consistent results? Are you confident that these two trials are correct? Explain why or why not.
Think about uncertainties in the instruments you used in the experiment. For example, when you used a pH
meter; a balance; a thermometer; or a burette; what happens if your instrument reads a slightly different value
from the actual value? How does a given error affect your results?
When fitting your data with a straight line, select the section of data points that is linear. You must use
most (80-90%) of the data points for your linear fit. Exclude data points at the very start or at the very end of
the line if they deviate significantly from the line. Display the equation of the line and the R-squared value.
The R-squared value is the correlation coefficient between the x and y values. A correlation coefficient of 1
indicates a perfect correlation. A value of 0.9999 or 0.999 shows the correlation is very good. Use your
Excel graphs, lines of best fit, and R2 value as supporting data to explain possible errors or the accuracy of
your results.
e) Write your discussion yourself – not with the help of your lab partner or other students! All work in writing
your discussion must be your own. Plagiarism will result in a zero for the entire lab report and will be
reported to the student conduct committee. Write in complete sentences. Write concisely. Be sure to cover
everything in the grading rubric. There is no need to give details of the procedure; do not state exact amounts
of a given solution or types of glassware used. Avoid being redundant between sections.
f) Type your discussion and select a font size of 11 pt or 12 pt. The line spacing should be 1.5 lines or doublespaced to give the TA enough space to write comments for you. The ideal discussion will usually be 1 to 1
1/2 pages in length. This is an appropriate amount of space to explain everything required by the grading
rubric. Discussions should never exceed 2 pages.
g) Use passive voice instead of first person (i.e. we / I / our / etc.). For example, instead of “We mixed the
solution,” say “The solution was mixed.” Instead of “We titrated the sample with…,” say “The sample was
titrated with….” It is understood that you are the one who did the experiment.
h) Proofread!