to How Write a Lab Report:
This is a brief explanation of how to write a proper organic lab report. As previously stated, your
lab reports will be divided into three main sections: The Pre, In, and Post labs. Lets take a look
at how these sections are organized and what sort of information should be included in your
write-up.
The Pre-Lab consists of the following:
I. Title:
This section is self explanatory. You should not simply transcribe the name of the experiment
from your lab manual. Instead, pick a unique and descriptive title for your report that clearly
states what you will be trying to accomplish in lab as well as how.
II. Introduction:
This should be a short paragraph explaining the nature of the experiment and its overall purpose.
This information will be garnered from reading through the background material for both the
laboratory procedure and the techniques that you will be utilizing during the course of the
experiment. Incorporate this information into your introductory statement. Your introduction
should answer the following questions:
What will I be doing in lab today?
What is the purpose of the experiment?
What techniques/apparatus will I be using to accomplish this task?
If the experiment entails a purely physical change/conversion (recrystallization, distillation,
etc) this is where your introduction will end. If, however, the experiment will be undertaking
a chemical transformation (reaction), you will need to add two additional pieces of information
to your introductory paragraph: a balanced equation and a reaction mechanism.
Balanced Equation:
In an organic lab report, a balanced equation is always written using either skeletal or condensed
chemical structures.
Never present your balanced equation using molecular formulas
This is a structural summation of the chemistry that you will be performing during your
laboratory exercise. Remember to check your stoichiometry very carefully. The following is an
example of the balanced equation for the double dehydrohalogenation of 1,2dibromocyclopentane:
Reaction Mechanism:
The final part of your introductory paragraph will be a reaction mechanism. As you will learn in
your lecture class, a mechanism is a stepwise, graphical depiction of a chemical reaction. It
shows (via arrows) all bond formation and cleavage that occurs during the course of a reaction.
It tells the story of how the starting material is converted into the product specified in your lab
handout. The reaction mechanism for the double dehydrohalogention of 1,2dibromocyclopentane is provided below as an example:
III. Safety Information:
Any and all relevant safety information pertaining to the current experiment will be provided in
this section. This information will come from two sources: the lab handout itself and the
individual MSDS (material safety data sheets) for the chemicals that will be utilized during the
experiment. This may be presented in either paragraph or bulleted form. Your TA will give you
specific instructions concerning how they would like to see your information organized. Be
thorough and make sure that you are mindful of all safety guidelines while working in the
laboratory.
IV. Table of Reagents:
This is a carefully organized list of all physical data pertinent to the current experiment. It is
only necessary to list the data that will be of direct use during the course of the lab. For instance
it is not necessary to list the boiling points of the solids in your first experiment
(recrystallization) as you will only be comparing their melting points to the data you collect
during lab. You must provide the compound name, structure, and molecular weight for all of the
reagents used in lab each week. Additional information should be included as needed (MP, BP,
density, etc...). All of the data that you will need to include in your table is easily obtainable by
simply typing the compounds name into an internet search engine like Google.
Sample table of reagents:
V. Experimental Procedure:
Each student will need to carefully paraphrase the experimental procedure presented in the lab
handout and record it in their notebook. Do not copy the procedure verbatim. Use enough detail
so that if your TA were to require you to perform the experiment using only your version of the
procedure, you would be able to complete experiment the accurately. Make sure that you have
included all weights, concentrations, volumes, etc necessary for the successful completion of
the lab. If you are using a new glassware apparatus (ie simple/fractional distillation, reflux,
etc) during the experiment, you must also include a detailed diagram in your procedure. As
with your safety information, this section may be presented in either paragraph or bulleted form.
Your TA will give you specific instructions concerning how they would like to see your
information organized.
The In-Lab consists of the following:
I. Data and Observations:
This is the section of your notebook where you will be recording all of your significant lab
results each week. Organization is key. Lab information typically falls into two main
categories: data and observations. Examples of typical lab data include: weights (starting
materials, products, drying agents), volumes (mL), temperatures (ie. MP, BP), and time (ie.
reflux or distillation duration). Your observations will include items such as color change (ie.
clear to cloudy, red to blue), smell (sweet, acrid, pungent), crystal texture/appearance (ie.
granular, needlelike, fine, coarse), and solution viscosity/appearance. Some examples of
common laboratory observations have been provided below:
When the solution was heated to reflux its color changed from clear to deep blue
After cooling the reaction flask in an ice bath for five minutes, white, needlelike crystals
began to form in solution
Addition of HCl (aq, 1M) to methylene chloride resulted in the formation of two
immiscible layers within the reaction flask. The top layer was clear and the bottom layer
was bright yellow.
Make sure that you are recording all of your data and observations in appropriate detail directly
into your laboratory notebook. Scraps of notebook paper can be easily lost or misplaced.
Without your data, you will not be able to complete your Post-Lab write-up.
The Post-Lab consists of the following:
I. Results:
This is where you will be performing and recording your laboratory calculations. In addition to
these computations, you will also present any graphs or diagrams that you have been asked to
generate from your data. This section will contain information such as:
Theoretical yield
Percent yield/recovery
Limiting reagent calculations
Extraction flowcharts
Data graphs (distillation temperatures vs volume)
Rf values (TLC)
There is a wide variety of information that can be included in the results section of your lab
report. The contents will change subtlety based on the nature of the laboratory experiment you
are working on. Your TA will provide additional information pertaining to what they would like
to see in your report.
II. Discussion/Conclusions:
In this section, you will comment on both your recorded data and observations as well as the
calculations generated in the results section (ie. yields, graphs). All data must be described and
evaluated in comparison to recorded literature values. This is where you will get the chance to
clearly explain what your data means. Do your results make sense to you? Are they reasonable
considering the parameters of the experiment? If not, what may have happened to cause an
aberration? Was it the result of a mistake in your experimental procedure? If so, what was the
nature of the mistake? If you are trying to identify an unknown compound, you will need to
indicate its identity and make use of your data to explain your reasoning. One of the most
common mistakes made by students is to pad their discussion section by restating the
experimental procedure. This is unnecessary and frowned upon. You will only need to
comment on procedure while attempting to explain any experimental mistakes that may have
affected your results (ie. loss of yield, introduction of impurities). Simply stating that impurities
are the reason for skewed data is insufficient. You must always indicate what the
impurities/byproducts are and how they might have been introduced into your experiment.
III. Post-Lab Questions:
Questions specific to each of your experiments and learned laboratory techniques will be
provided to you at the end of lab each week. They will be posted on ELC separate from your lab
handout. The answers must be written in your laboratory notebook.