Lab Reports
 modified Sept 18, 2012
   GENERAL RULES:  Lab reports should be produced on a laser printer or ink-jet printer; they must be printed on one side of the page.  The text must be double-spaced.   Take care to use correct superscripts and subscripts when writing chemical and algebraic formulas.  All but the simplest mathematical equations should be created using the word processor's equation editor.  If you place a chemical structure from ChemDraw into the document, make sure that the image is appropriately sized.  All pages of the lab report should be numbered except the cover sheet.  The page bearing the title and abstract is page number 1.  The final page of your report should contain "Literature Cited".

    Tables  and figures are numbered separately throughout the report; in the text, always refer to the figure or table by its number so there is no ambiguity.  For tables, the table number and title appear at the top of the table.  Tables should be compact: single-space the data; even use a smaller font if necessary.  It is often useful to have a footnote under the table with helpful information about the data.  Figures should have the figure number and caption placed immediately underneath the figure. At the very least, the caption should explain the source and purpose of the figure.   Graphs and other figures should be made conveniently sized.  Both tables and figures should placed in the document as close as possible to their first mention in the text. 
    Remember: Title and number at the top of a table.   Figure caption and number below the figure; no box around the figure.

    Place a cover sheet on top of the report.  The cover sheet should bear a descriptive title for the experiment, your name, the name of your lab partner, and the date of submission for the report.  The title of the experiment should also appear at the top of the first page.  Do not number the experiments.  Do not place your name or your lab partner's name on any numbered page of the lab report.   If you share data from other groups, you should label the different sets of data by the groups' initials, not their names.

    Have your lab partner read your complete lab report and fill out the evaluation form.  Read the evaluation and decide if you want to make changes to your report.  Then turn in the report and the evaluation form.
 
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To the greatest extent possible condense data and numerical results into tables and graphs for easy reading.
  Tables:    Tables of data or numerical results are single-spaced and should be produced using the wordprocessor's table routine or pasted into the document from EXCEL.   It is customary in science to organize tables so that numbers with the same units are in the columns.  The columns must be labeled and units specified. Use abbreviations in the column headings.  Do not allow the  headings to make the columns unnecessarily wide--abbreviate!  Your goal should be to make each table as compact as possible, and in that regard, it is not important that two or three tables have the same size (especially width).  But you don't want the table to bust out of the margins of the page--if the table needs to be very wide, you should probably rotate the table and print it in landscape format on the paper.  Do not insert insignificant digits in the table.  Generally, numbers in the table should be rounded off according to the least count of the measuring instrument, or if they come from a LS fit, they should be rounded in accord with the error from the fit.  To represent numbers compactly, you can multiply them by an appropriate factor of ten, but be sure to indicate that in the table.   Sometimes you will have so much data that a table is unwieldy, so just graph the data -- a good example is the case of an absorption spectrum where you have hundreds of points.
    All tables must conform to ACS style: no vertical rules!  If you copy data from EXCEL into WORD, Word will create the automatically create a table without ruler lines.  Simply add ruler lines from the BORDER tool.  All you need are three lines, a line above the column headings, a line underneath the column headings, and a line at the bottom of the data.
EXAMPLE TABLES  The first is good, the second is not.
Example tables pdf file
  Figures:  Graphs of data are the most common kind of figures in a document, but not the only kind.  Figures are any graphical object in the document, such as a picture or drawing of the apparatus.  In chemistry manuscripts,  chemical structures are the only kind of figure that is often not counted as a figure in the manuscript, simply because in some manuscripts there are so many.  In a p chem lab report, a structure drawing of the most important molecule in the experiment probably should be counted as a figure and so labeled.  Always use a caption with a numbered figure. 
    Advice for graphs: Make sure that axes are labeled and units are specified; the y axis label should be printed horizontally for easy reading.  Abbreviate axes titles if they are too long.  A title at the top of the figure is not necessary and should be very terse, because all the important information about the figure should be in the caption underneath.   Very important: Draw lines for functions, especially fit functions, use markers only for data.  If you do a LS fit, draw the fit line (very thin) thru the data (markers).  The only exception to this rule is a case where you have so many data points that markers become ugly; a good example is the case of an absorption spectrum (abs vs wavelength) (where a line representing the spectrum is expected anyway).  A digital spectrometer would give you hundreds of data points; markers just don't work in that case.
    Excel isn't especially good at producing good-looking scientific graphs--graphs from Excel always need some extra attention.  You should almost always use an X-Y scatter plot, unless you are doing something very special.  Remove the horizontal grid lines, and remove the outer box around the graph.  Delete the legend, or move it into the plot area.  Be aware that sometimes Excel makes strange choices about the limits of your axes; examine the axes limits to make sure they are appropriate.  Also, you may need to change the axes if you are trying to do an important extrapolation of the data.  Trend Line is actually quite good at extrapolation; that might be its one redeeming feature!
EXAMPLE FIGURES The first is good, the second is not.
Example figure pdf file
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   REPORT SECTIONS: I strongly suggest the following outline for your lab reports, although for some experiments certain sections may not be needed. When writing the lab report, remember that the important ideas to communicate are the results of your measurements, the analysis of the data, and the conclusions you can draw based on your results. Many of the sections of the lab report, especially data analysis and sample calculations, will help you think about your results. When you include a section, label it!

COVER SHEET  
    Experiment Title that is descriptive of what you studied or the goal of the experiment
    Name
    Name of Lab Partners
    Date submitted (or resubmitted, if a rewrite is required)

   Abstract: A brief paragraph on the question your experiment attempts to answer, and the important results (numerical results) and conclusions you have made from the experiment. Other students should be able to read your abstract and decide whether they are interested in the rest of the report. The abstract DOES NOT contain a description of the experiment or background information behind the experiment.
Abstracts that begin with "The purpose of this experiment was ..." or "We did this experiment to find out ..." are usually inappropriate.  These sentences belong in the Introduction.  A good starting sentence for an abstract is "Our investigation of [  ] revealed that ..."  That start leads directly to results and conclusions.  Get to the numerical data and conclusions immediately!
   Introduction: A few brief paragraphs on the reasons for doing the experiment.  What is the question about Nature that you hope to answer?  Why is the question important?  Discuss what you already know and what you hope to learn.  Any theory or prior experiment that is related to the current question should be discussed here.  This is where you should place important background information, such as chemical theories, chemical structures, or mathematical equations.
Sentences that begin "The purpose of this experiment was ..." or "We did this experiment to find out ..." belong here!
 If the molecule under study is big or unusual, like azulene, this is the place to insert a chemical structure from ChemDraw.
Any physical or statistical equation that is important, such as the Nernst equation or the t test, should be inserted here using the equation editor in Word.
   Experimental Method: A brief outline of how the measurements are made. In many cases a figure that is a nice drawing of the apparatus will be helpful. You should not describe in detail how the experiment was performed; instead, reference the source of your procedure.
 
   Raw Data: A presentation of the measurements you made during the experiment. A table or graph will usually help the reader absorb the data.  Place several sets of data on one graph for easy comparison.  Show all the data you took. If you reject some of the data from further analysis, explain why.
 
   Data Analysis: Describe the method of analyzing the data that you used to determine any physical or chemical constants. Be sure to include a sample calculation so that others can follow your calculation. If you used a computer program, be sure to mention which program you used. If you wrote the program, include a copy in an appendix to your report.
Never present the numerical results of a least-squares fit without an accompanying graph.
On the other hand, never use Trend Line by itself, because it can't provide you with fit errors.
The fit function should be graphed as a smooth thin line and the experimental data should be plotted as individual points (markers).
The outer box around an Excel chart should be removed before it is pasted into any other document.
Usually you should remove any extra grid lines from the graph.
Never copy the entire output of an Excel regression into a Word document without editing it to
remove the unneeded words and statistics.  Usually your best method is to copy the data from Excel into Word; Word will automatically assume it is a table.
All tables must conform to ACS style: no vertical rules!  In Word add horizontal rules using the BORDER tool under Paragraphs.
  Error Analysis: Determine the 95% confidence limits of the physical or chemical constant you found during the data analysis. Compare your constants with the literature values and determine the accuracies (percent error). Did the correct answer fall within the confidence limits you computed? If not, why not?
This is the appropriate place to discuss determinate sources of error; that is, errors that could have thrown your value off either too high or too low.  Generally, if the accepted value is outside your 95% confidence limits, then your experiment suffers from some determinate source of error, and you should attempt to find out what it is.  Usually a few careful control experiments will help you track down the source of error.  But you can't wait until you write your report to do that!  You've got to think about it while you apparatus is ready!
   Conclusions: Bear in mind that your conclusions are the most important part of the report. You do an experiment to answer a question about Nature. The answer to the question should be the focus of your conclusion. The preliminary sections of the report simply provide the reader with the background needed to accept your answer. ANSWER THE QUESTION!
      A good way to organize your conclusion is to create a Toulmin analysis of your argument.  Be explicit about your claims, your warrant, and your data (or grounds).  The discussion of your data will be clearer if you refer directly to tables, charts, pictures, observations, or graphs that appear earlier in the lab report.  You first job is to make sure that readers will understand your claims and the reasons for your claims.
    In addition, use the conclusion to think about the physical and chemical implications of your results. When you believe your results answer the question put to Nature, you should try to understand the physical and chemical meaning of your answer:  Does the structure of the molecule under study explain the result? In other words, why did you get the answer that you got? Mention other questions that remain unanswered, and propose further experiments that could answer them.  Could you do the same experiment on a different compound, or a different experiment on the same compound, that would answer other questions?  Many bad lab reports are written because students don't think about the meaning of their results.
    A Common Pitfall: The "Quality of the Data" Conclusion. Your conclusion should not say that you got "perfect" data or good data or acceptable data or bad data. The goal of the experiment is to answer a question about Nature, not to obtain "perfect" data. Getting "perfect" data is impossible!  Getting "perfect" data or even good data does not make you a scientist. You are a scientist when you ask questions about Nature and design experiments to answer them.  Many students misuse their conclusion in an attempt to explain why their data are bad or untrustworthy, so that they can avoid answering the question put to Nature.  This will not be permitted!
Random error exists in all experimental data -- multiple measurements and signal averaging will slowly remove random error from your results.  Much more insidious is determinate error -- the way to find out if determinate error exists is to run little control experiments throughout the course of the experiment.  Ask yourself at every stage of the experiment, "Does this make sense?  Can I believe these results?"
Data that are so "bad" that they do not answer the question will not be accepted. If an experiment is incapable of producing data good enough to answer the question, you must find out why. Therefore, you must repeat an experiment until it answers the question put to Nature, or until you understand why it cannot.

Literature Cited:  Be sure to cite the sources of your lab procedure, your data analysis, and any chemical information that you mention in the introduction and conclusion.  I am particularly looking for citations to related information you got from physical chemistry textbooks, physical chemistry laboratory textbooks, and articles in the Journal of Chemical Education.  As a general rule you should follow the citation conventions that you see in the Journal of Chemical Education.  Be aware that these conventions will surely be different from those you had to use in earlier writing classes.  Consult the ACS Style Guide or ask me if you have questions!


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   MATTERS OF STYLE: Write your report so that your intended audience is other physical chemistry students. This shouldn't be hard, since you will probably read a few old lab reports before you do the experiment, and remember that your lab partner must read your report.
    Sime has some good recommendations on matters of continuity and style, tense, voice, grammar, numbers, and proofreading.  Here's a quick summary:
Introduce tables and figures with one or two descriptive sentences above their location in the report.   Use the text below the table or figure to describe its meaning and significance.
Conjunctive Adverbs such as "above all", "rather", "therefore", and "however" will help your reader connect sentences and ideas.  Sime has more examples.
Keep your language simple.  Try to use short, common words and simple phrases.  Avoid fancy words and fuzzy phrases.  Sime has many examples of fancy words/phrases and simple alternatives; here are just a few:
                                        FANCY                                            SIMPLE
                                        ascertain                                           find out
                                        endeavor                                          try
                                        modification                                     change
                                        utilize                                               use
                                due to the fact that                                    because
                                    on account of                                       because
                                    in order that                                          so
                                    it is obvious that                                   obviously
Report your work in the Past Tense.
Use the passive voice throughout your description of the experimental procedure.
"10 mls of the NaOH solution were pipetted into the test tube and shaken until a precipitate formed.  The preciptate was collected by filtration on ashless filter paper."  Notice that we avoid "I did this" and "then we did that"; after three or four sentences of that stuff, you get this "sing-song" sound to the report that is difficult to read.
Watch out for dangling participles.  Passive voice descriptions of experimental procedures can become infected with dangling participles. 
"Using a 10 ml pipette, NaOH solution was added."  It's a dangling particple because the solution cannot use a pipette!
Switch to a prepositional phrase, or, on some occasions when clarity demands, switch to the active voice. 
"10 ml of NaOH solution were added with a pipette." OR "Using a 10 ml pipette, we added NaOH solution."
Report published results and accepted theories in the Present Tense.
"The voltage of electrochemical cells is predicted by the Nernst equation."
"Ethanol is a more polar solvent than hexane."
"The Nernst equation describes the relationship between cell voltage and chemical concentrations."
"Substitution reactions on primary halides take place via the SN2 mechanism."
Report your conclusions in the Present Tense.
"Our results show that NaOH is a stronger base than NH3."
"We found that azulene's heat of combustion is higher than that predicted using simple bond energies." 
 "Our results indicate that the unknown is iron sulfate."
 "We believe that the hgher temperatures resulting from the malfunctioning temperature controller caused the product to decompose."
Use the active voice during the introduction and conclusion.  Transitive verbs will help you out of the passive voice trap:  "Our results indicate ..."; "My experiments show ..."  "Our control experiment proved ..."  These are stronger, clearer sentences that make for better reading.  (I have no objection to personal pronouns in your lab reports; there's nothing wrong with an occasional "I" or "we".  CS)
Proofread a paper copy. Try reading the paper out loud.
 

Summarized from Rodney J. Sime, Physical Chemistry: Methods, Techniques, and Experiments, Saunders College Publishing, 1990.  Chapter 8, pages 165-175.

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CRAZY EXCERPTS:Try to avoid writing nonsense such as these examples of logical slips and brilliant bull, which are taken from real p chem lab reports.  I've included the comments I wrote in the margin of the report:

Means testing [of chloride percentage] is used to determine if the [unknown] sample is the same as the known ...
Means testing cannot prove that two substances are identical.  Two different chemical compounds could have the same chloride percentage.

... it was evident that our temperature readings were higher than expected.
By how much?  Don't leave your reader hanging by leaving out a crucial detail.
... we can attribute this systematic error to improper thermometer calibration.
Any assumption such as this should be tested independently.  Check the thermometer in an ice bath and in boiling water.  See the note above about Error Analysis!

    Raw Data
weight of hydrochloric acid = 0.734 g
I know you didn't weigh out the hydrochloric acid solution! That can't be "raw data"!
moles HCl = 0.20 moles
Watch out for zeros and sig figs!  0.734 g HCl = 0.0201 mole HCl

Heat capacity assumes ideal gas behavior as well as a reversible gas.
How do you shift gears on an ideal gas?  Processes are reversible, not gases!

CO2's trigonal planar configuration ...
Carbon dioxide is linear.  Check your Gen Chem book!

    Raw Data
 trial     mass                    volume                     calculated molecular weight
 1          .0912 g                 37.14 ml                        60.34 g/mole
 2          .1018                    42.33                             59.09
 3          .1008                    45.45                             54.49
The volume of a gas sample will be proportional to its mass.  In the calculation of molecular weight, we divide by volume.  Therefore the third molecular weight value is low because the volume is too large.
... acetone could have inhibited vapor molecules from displacing water in the burette, thus resulting in a volume for the third trial that was too low.
The volume's too large, not too small!  Your explanation is meaningless!

    Raw Data
trial    barometric pressure    temperature
1        745.74 mm Hg            20.6 C
2        745.74                        20.6 C
3        745.74                        20.6 C
... temperature and barometric pressure were closely watched during the experiment.  They remained approximately constant through all trials performed.
Why did you say "approximately"?  They never changed at all!
Possible causes of error in this experiment were variations in the barometric pressure, the temperature, ...
What variations?  Your data denies the existence of changes in temperature and pressure.  You are contradicting yourself.

    Error Analysis
The percent error in this experiment was quite large.  It was calculated as follows: % error = [(26.69 - 17.74)/26.69] x 100% =  33.53%.  However, it is hard to say how accurate this experiment can be.  There exists no value with which to compare our experimental value.
You have just contradicted yourself; percent error is a measure of accuracy.

All three trials fell within the 95% confidence limit.
Completely unsurprising!  The important question is, does the accepted literature value fall with in the the confidence limits.

The reason for the large variance is because the trial is so far off from the actual molecular weight, due to a high standard deviation.
Statistical nonsense!  Variance is just the square of the standard deviation, so if one is high, the other will be too.  This statement confuses accuracy and precision--it suggests that bad accuracy causes bad precision.

... the average of the three trials differed from the accepted value by only 3.56%.  However, when you take a closer look, the results from sample 3 should disturb you.  It differs by 9.33% from the mean.
Whoa! Why did you switch from comparing against the accepted value to comparing against the mean?
This shows that the results from the other two trials are good enough to save the combined results.
Statistical nonsense!  Results cannot "save" other results.  Many repetitions of an experiment allow random errors to cancel out when the average is computed.  That's not salvation!

... because the reciprocal of temperature is taken, a small error in the temperature means a huge error in the reciprocal.
Sounds like what you need is a big error in temperature so you'll get a small error in the reciprocal!

In retrospect, we shouldn't have been so zealous to get as many points on the graph.  We should have had fewer points ... More actual points would fall on the best straight line in this case.
Great idea!  You should probably have gotten just two points, so that they will both fall exactly on the best straight line!

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