Chemistry 211
Clark Collge
Writing a Experimental Procedure Section
An experimental section is designed to give the reader (an experienced chemist such as
yourself or your instructor) a succinct procedure that can be used to perform the experiment. This is
probably the most difficult section of a lab report or paper to write. This section should summarize the
procedure as performed in the lab, including what solvents were used, temperatures, quantities, a
special apparatus, etc. The synthetic and analytical methods should be stated, but, as in the
introduction and abstract, procedural details should be omitted. For example, it is not necessary to
give every step of the recrystallization, rather you should state that a recrystallization was performed,
and provide the solvent used (and charcoal, If used).
When describing a procedure, include the amounts of reagents actually used, as accurate
masses or volumes, and the number of moles used for the reactants only. Also list specific glassware
used only if it is particular to the technique (routine beakers, round bottoms and flasks are not
necessary to list), list reaction times and list temperatures for reactions. You should not describe how
to set up a particular apparatus unless it is unusual. Also, specify the amounts of product isolated, both
crude and purified, the percent yields, mp/bp, and any diagnostic spectroscopic information. Key
observations should also be included, such as color changes, phase changes, formation of a gas or a
precipitate.
A well-written Experimental section will allow the reader to carry out the reaction as you did, and
to have some idea of what to expect as the reaction proceeds. It is written in complete sentences and
in paragraph format. Don’t forget to use complete sentences- you should not write a list of commands
or instructions, rather a coherent paragraph. If only one compound was made/isolated, your procedure
section should only be one paragraph. For a multi-step synthesis, use a separate paragraph for each
product isolated.
The following example procedure is for the synthesis of 1,2-dibromocyclobutene.
Potassium hydroxide (KOH, 92.2 g, 1.65 mol) and 300 mL of absolute methanol
(HPLC grade) were placed together in a 1-L round-bottomed flask under Argon at 25°C.
The mixture was stirred until no KOH solid remained in the flask. A solution of 1,1,2tribromocyclobutane (73.2 g, 0.25 mol) in methanol (166 mL) was added. Immediately
white potassium bromide began to precipitate out at 25°C. The solution was then
heated to reflux and stirred at reflux for 2 hours to give a yellow solution. The reaction
mixture was then poured into a 3-L separatory funnel containing water (400 mL), in order
to oil out the product. A heavy, slightly yellow-green oil separated out of solution and
was drawn off. 800 mL of diethyl ether was then added to the extracted oil. The
aqueous phase was washed with an additional 500 mL of ether, the two ether extracts
were combined, and the resulting solution was dried over magnesium sulfate. The ether
was removed by rotary evaporation to yield 50.7 g (87%) of crude product. The product
was fractionally distilled under vacuum (100°C at 1 mmHg) to give 47.2 g (81% purified
yield) of a pale yellow liquid. 1H NMR (CDCl3): 2.86 ppm (2H, s).
Some notes/reminders from the above examples:
1. Mole amounts were provided for the reactants ONLY, not for the solvents. Quantities were
provided for all reagents.
2. I did not describe how to set up a reflux apparatus, or how to use a separatory funnel. You
should assume that the reader knows how to do this! (You will learn!)
3. The last one or two “sentences” always provide the information about the product: the mass, mp
or bp, % yield, and a description of the product. Spectroscopic data (the NMR in this case)
follows the “results”.
4. Only one compound was made, so the experimental section is only one paragraph. The crude
product does not count as a separate compound!
5. Note that the names of all compounds are written out for the first time. If a compound is used
again, the formula should be “defined” before it can be used.
Writing an Experimental Section
Fall 2007
Page 1 of 2
Chemistry 211
Clark Collge
The following checklist may assist you in writing the Experimental section of your report. You will not
need all of these for each experimental section – this is a list of the possible items to include in your
report.
• Quantities of all reagents in grams or mL, and in moles for stoichiometric reactants (include
densities for liquid reactants).
• Solvents and amounts used.
• Apparatus description (size and type of glassware, if it is unusual).
• Reaction conditions, e.g. reflux, temperatures, times, cooled on ice, etc…
• Crystallization solvents.
• Extraction: specify solvent, volume, and number of extractions (e.g. 3 x 50 mL water).
• Drying agents.
• Rotary Evaporator (Rotovap): “The solvent was removed through rotary evaporation” or “the
solvent was removed in vacuo”.
• Filtration methods.
• Chromatography: specify stationary and mobile phase, as follows:
o TLC: type of plate and solvent
o HPLC: type of column and solvent
o Column: adsorbent and solvent(s)
o GC: type of column, carrier gas and temperature
• Distillation: type (simple, steam, fractional) and temperature at which the distillate was collected.
• Product information.
• Physical description, liquid or solid, crystalline or powder, color, odor, if any.
• Actual yield, in grams or mL and percent yield.
• Melting or boiling point (include range).
• Spectroscopic data, as follows:
o IR: specify method of sample prep and one or two diagnostic frequencies
Example: IR (nujol mull): 1700 cm-1 (C=O), 1450 cm-1 (CH3)
o NMR: specify solvent and spectral features, in the following format: chemical shift in ppm
(integration, splitting pattern). For splitting patterns: s = singlet, d = doublet, t = triplet, q
= quartet, m = multiplet
Example: NMR (CDCl3): 1.2 ppm (3H, t); 2.4 ppm (3H, s); 3.8 ppm (2H, q)
• For a multi-step synthesis, report an overall yield, which is the product of the yields of each step.
You may also consult for a similar explanation and examples of an experimental section:
http://d.web.umkc.edu/drewa/Chem321L/Handouts/321L%20Experimental%20Section%20for%20Lab
%20WriteUPs.pdf
Writing an Experimental Section
Fall 2007
Page 2 of 2