FORMAL WRITTEN LABORATORY REPORTS
–
HERSHEY HIGH SCHOOL
Introduction
An important part of the training of every young scientist is the ability to write a scientific report.
Too often this skill is reserved for upper-level courses or even postponed until graduate school,
often with abysmal results. It is therefore important to introduce students to “correct” scientific
writing early in their careers. Of course, every journal and every instructor has its/his/her own
rules for what this “correct” way of writing is. Thus, it is important in each case to read and
understand the guidelines given by the instructor or by the scholarly journal to which one is
submitting the report. The goal of this document is to present students with some of the rules for
writing a scientific paper that will be consistent among ALL Hershey High School science
courses.
Sections of a Lab Report
Almost every scientific paper contains the following sections in this order of coverage: title,
abstract (not relevant for our labs), introduction, experimental method, results, discussion, and
references. Some general guidelines for each of these sections follow:
1. Title: The title should reflect the report’s content. It should be brief, specific, and
descriptive. Be sure to note the independent and dependent variables. If you are unsure about
these terms, look them up or ask a teacher.
2. Introduction: The introduction should present a clear statement of the goals of the research
and should answer the question of why the research is important. It might also include a brief
description of the background of the problem, complete with relevant references to the
literature to describe what others have accomplished in this area of research and how this
project complements or improves upon their work. For purposes of our class, the Introduction
section should also include a brief description of the theory behind the experimental technique
which is employed in the project. It should also explain any equations used in the calculations
and define their variables.
3. Experimental Method: The experimental section should describe the actual procedure used
in the course of the experiment (it should not simply be a repetition of the directions in the
laboratory manual) given in enough detail so that the experienced reader could reproduce your
work using only the Experimental section of your paper as a guide. This entire section should
be written in the third-person, past-tense, and passive-voice. For example, one would say that
“Fifty-milliters of 0.20 M HCl were added to a 250-mL Erlenmeyer flask and titrated with
0.050 M NaOH until the phenolphthalein indicator changed from colorless to pink.”
Calculations are typically not included in this section.
4. Results: Use the Results section to present only the relevant data. Record volumes, readings,
etc. Present data for multiple samples in table form. Also include in this section any relevant
graphs of the data or spectra. Be sure that graphs and figures are correctly labeled as described
in a later section of this handout. Always refer to the data in figures and tables in the text by
mentioning the figure or table number. Be careful not to draw any conclusions about the
experimental data in this section. Reserve the actual analysis of the data for the Discussion
section. For purposes of this course, a Sample Calculations section, showing one calculation of
each type (including units), should be included immediately following the Results section,
when requested by your instructor.
5. Discussion: State all conclusions as specifically and as objectively as possible. This is the
section where the experimental results should be interpreted. Any references to particular
sources of error should be specific in nature and should match It is also good practice to
include a discussion of the limitations of the work in this section and suggestions as to how
the work could be improved by further experimentation. Thus, for instance, if the
calculated volume of H2O entering a dialysis bag is too high and you state that you might have
made the bag hypotonic, you would lose points because the dialysis bag H2O volume would
increase if the bag were hypertonic. Although many scientific journals allow the use of firstperson in this section, try your best to avoid this temptation and to continue to write in thirdperson whenever possible.
6. References: Scientific journals have lengthy instructions for the format of references.
Fortunately, very few references will actually be needed for lab reports in introductory courses.
Most, if not all, of your high school course references will follow the MLA format. Our HHS
library contains an extensive resource network. Therefore, your references should NOT
contain a majority of random websites.
Some comments about grammar, style, and usage
1. The subject and its verb should be in agreement. For example, “the experimental data are
given in Table 7,” not “the experimental data is given in Table 7.” The word data is plural.
Likewise, “a series of compounds were tested,” not “was tested.” Units of measure are treated
as collective nouns and are therefore singular. For instance, “5 mL of water was added,” not “5
mL of water were added.”
2. Capitalize only proper nouns. Do not capitalize the common names of element, chemicals,
or equipment. Correct: “a Perkin-Elmer LS-5 spectrofluorometer was used to determine the
emission spectrum of anthracene.” Do capitalize the elemental symbols (e.g. H, He, Li).
3. Numbers reported with units should be listed in numeral form, followed by a space and then
the abbreviation for the unit. Always include a space between the number and its unit and use
the correct abbreviations for units: e.g. g for grams, s for seconds, h for hours, min for minutes,
s for seconds, mol for moles, mL for milliliters, K for degrees Kelvin, and °C for degrees
Celsius. Numbers used as adjectives should be hyphenated: “3.45 g of sodium sulfate was
added to a 100-mL Erlenmeyer flask.” Counting numbers (numbers without units) ten or
smaller should be spelled out: “Eight test tubes were prepared and they were each mixed by
inversion ten times.” Whenever a number begins a sentence, both the number and its units
should be spelled out in their entirety. Try to avoid beginning sentences with numbers
whenever possible. Ranges of numbers should be reported with dashes and the units following
the latter numeral: e.g. “in each experiment, 0.20–0.45 g of FeCl3 was used.” A series of data
with the same units should contain the units only after the final data point: e.g. “IR peaks were
observed at 3200, 2894, 1730, 1450, 1260, 985, 750, and 450 cm-1.”
4. The third-person, past-tense, and passive-voice should be used for all experimental
procedures. Do not use the words “I” or “we” in the Experimental section. “I” and “we” are
permitted in the Introduction and Discussion sections, but their usage here should also be
minimized whenever possible. Correct: “The 0.20 M KMnO4 solution was added to the 500mL beaker which contained 0.20 M KI,” and “The results of this work indicated that the
temperature dependence of the rate constant for the reaction of X with Y was exponential.”
5. Number the pages of your lab report using Arabic numerals in the upper right-hand corner.
Do not, however, number the first page.
6. Figures should be numbered with Arabic numerals and referred to at the appropriate place in
the text. Do not refer to a figure by writing “see Figure 2.” Instead, report that “the results of
the pH titration are shown in Figure 2.” Each figure itself should be labeled with the figure
number and a thorough description of the contents of the figure. The figure caption should be
detailed enough that it could stand alone in describing to the reader exactly what data it
contains and what experimental conditions were used in the collection of that data. The axes of
graphs must be correctly labeled, including units. Graphs should be of an appropriate size such
that the data are easily seen and that the points fill the entire section of the paper reserved for
the graph.
7. Tables are also numbered sequentially using Arabic numerals (1, 2, 3, …). The same rules
for referencing tables in the text and for labeling tables with descriptive captions apply to
tables as they did to figures.
Printed with permission from Dr. Brian Pfennig, Ursinus College
Checklist Before Turning in the Lab Report
____ The project number, title, name, and date are included
____ The Introduction section presents an overview of the work and the reasons for doing it
____ The Experimental section is detailed enough so that a knowledgeable researcher could
repeat it using only what you have written in this section
____ The Experimental section is written in the third-person, past-tense, passive-voice
____ All major results are included in the Results section
____ Multiple, related results are tabulated with appropriate table headings
____ The units for numbers in tables are given only in the column headings
____ The Results section refers in the text to any figures and tables by number and describes
their contents, but it does not interpret the data
____ The Sample Calculations section contains only one set of the important calculations
(including units)
____ The Discussion section explains the significance, trends, and limitations of the data
____ All pages after the first page are numbered in the upper, right-hand corner
____ There is a space between each number and its units
____ Subscripts and superscripts are typed, not hand-written
____ Each figure or table has a stand-alone, descriptive heading
____ The data in figures or tables are organized and have units
____ The paper was spell-checked and sounds fluent when read aloud
____ Any graph fills the entire page, the axes are labeled, units are included on the axis labels,
& the range is such that the data fill the page
Formal Lab Report Assessment
Section
Components
Points
Earned
Max
Points
Independent Variable
1
Dependent Variable
1
Object(s) being investigated
1
Background information
2
Goals of the research
1
The hypothesis
1
Explanation of any equations used
1
Description of actual procedures
3
Experimental
Method
Not a reiteration of procedures from lab
manual
1
(Procedures)
List of materials required
1
No “I’s” or “We’s”
1
Title
Introduction
Present Tables and Figures that are:
Results
Discussion
-introduced in the text
2
-labeled and numbered properly
2
-meaningful
2
-organized
2
-clear
2
Sample calculations section
2
Interpret Data
1
Make a conclusion regarding hypothesis
2
Limitations of this work
Suggest additional experiments
2
Relate study to outside world
2
2
References
Total
Proper MLA format
3
Not exclusively Websites
2
40
Example Lab Report
Project #52: Determination of the Empirical Formula of
Magnesium Oxide Formed by the Combustion of Magnesium Metal in Air
Zaccharias Ursinus
April 1, 2006
Introduction
When calcium carbonate, CaCO3, is decomposed by heating, it emits gaseous carbon dioxide
and a white solid called lime, which glows brightly when heated. By measuring the volume of
CO2 gas emitted in this process and then weighing the amount of the solid calcium oxide that
remains, Watkins determined the empirical formula of lime to be CaO. Since magnesium
contains the same number of valence electrons as Ca and lies directly beneath it in Mendeleev’s
table of the elements, the purpose of this work was to ascertain the empirical formula of
magnesium oxide. Magnesium oxide can be produced by the combustion of magnesium metal in
air according to the procedure employed by Pfennig. The combustion of magnesium in air,
however, also leads to the formation of magnesium nitrides, previously making gravimetric
analysis of magnesium oxide impossible since the relative amounts of magnesium oxide and
magnesium nitride formed in the combustion process are unknown. This work avoids that
complication by converting the undesirable magnesium nitrides into magnesium hydroxide first
and then quantitatively converting the magnesium hydroxide into magnesium oxide.
Experimental Method:
Three ceramic crucibles and their lids were heated with a Bunsen burner until they were red
hot for at least 10 min. The crucibles and their lids were then removed from the flame by using a
pair of tongs and carefully placed in a desiccator to cool. After the crucibles were cooled to room
temperature (~25 °C), their masses were obtained to the nearest 0.0001 g using a Mettler
analytical balance. This procedure ensured that any adsorbed water on the surface of the
crucibles was completely driven off before the crucibles were weighed. Several pieces of freshlysanded magnesium ribbon having masses of 0.24–0.32 g were carefully weighed to the nearest
0.0001 g on the analytical balance. The Mg pieces were placed inside the previously-weighed
crucibles with the lid slightly ajar and heated to red heat using a Bunsen burner. After 10 min in
the Bunsen burner flame, the crucibles were cooled to room temperature. A small portion of
distilled water was added to each crucible in order to wet the solid contents of the crucibles. This
procedure converted all of the magnesium nitrides formed by the combustion reaction into
magnesium hydroxides. The crucibles were again heated in a Bunsen burner flame, at first
slowly to drive off any excess water without splattering and then to red heat for at least 10 min.
After cooling the crucibles to room temperature in a desiccator, their masses were again obtained
to the nearest 0.0001 g using an analytical balance.
Results:
The masses of the magnesium metal used, the masses of the magnesium oxide formed, and the
percent magnesium by mass for each trial are listed in Table 1. The average percent magnesium
was determined to be 60.28% with a relative average deviation of 0.5 ppt. Assuming that all of
the magnesium metal got converted into magnesium oxide, the empirical formula of the
magnesium oxide is MgO.
Table 1. The masses of magnesium and magnesium oxide, and the mass percent magnesium in
magnesium oxide determined gravimetrically by the combustion of magnesium ribbon in air.
Trial number
1
2
3
mass of Mg (g)
0.2513
0.3044
0.2792
mass of MgO (g)
0.4166
0.5049
0.4635
average:
Percent Mg (%)
60.32
60.29
60.24
60.28
Sample Calculations:
% Mg = 100% * (0.2513 g / 0.4166 g) = 60.32%
RAD = 1000 * (0.04 + 0.01 + 0.04) / (3 * 60.28) = 0.5 ppt
Discussion:
When magnesium metal is heated in air using a Bunsen burner, a mixture of magnesium oxide
and magnesium nitrides is formed. The addition of water to magnesium nitride results in the
formation of magnesium hydroxide. When magnesium hydroxide is heated in a Bunsen burner, it
is quantitatively converted into magnesium oxide. The net result of this procedure is the
complete conversion of magnesium metal into magnesium oxide. By knowing the exact masses
of magnesium that were combusted and the mass of magnesium oxide that was formed, the
percent magnesium in magnesium oxide was determined. Since the molar masses of Mg and O
are known to at least five significant figures, the exact stoichiometry of combination was
calculated to occur in a 1:1 Mg:O ratio. This empirical formula, MgO, is consistent with the
known tendency of Mg to form 2+ cations and O to form 2- anions, as well as with the
stoichiometry of calcium oxide previously determined by Watkins.1
The reproducibility of the three percent magnesium measurements is reasonable (0.5 ppt).
However, all three of the experimental values are slightly less than the predicted percent
magnesium based on the molar masses of Mg and O (60.30%). A possible explanation for this
result is that some of the MgO might have been lost as smoke if the crucible lid was too ajar or if
the magnesium ribbon was heated too rapidly. If this were the case, it would result in an
artificially low yield of magnesium oxide and therefore a smaller than actual percentage of
magnesium.
References: