Writing a Lab Report
There are 3 distinct parts of a good lab report: Experimental Planning and Design, Data
Collection and Analysis, and Conclusions and Evaluations. Not every part of each
section needs to be included. Check with your teacher to determine what is needed for
your lab report.
Section One: Experimental Planning and Design
1. Background research
Background research should be done to provide introductory information to support why
you are doing the lab and to also to define vocabulary. You might use a variety or
reference materials for the topic such as textbook, lab book, Internet search or scientific
journals.
2. Question
A question is formed to establish what you are seeking to learn based on your prior
knowledge about a topic or subject or through your background research.
3. Purpose
The purpose is a series of sentences that expresses what you are trying to prove or
identify in the lab.
4. Hypothesis and Prediction
The hypothesis and prediction state what you believe will happen based on background
information. These statements can be both qualitative and quantitative.
5. Independent variable (experimental variable)
The independent variable is the factor changed by the person doing the experiment. This
is the one you manipulate or vary during the experiment.
6. Dependent variable
The dependent variable changes in response to the independent variable. It is the one that
is measured by you during the process of the experiment.
7. Controlled Variables
Controlled variables are held constant so as not to directly effect the independent and
dependent variables.
8. Materials
The materials section should list all equipment and other materials needed to conduct the
experiment. Be specific by including sizes and amounts.
9. Procedure
The procedure is a step-by-step account of what you did in the lab, no matter how
insignificant it may seem. You are to assume that if someone should pick up your report,
that they should be able to follow your steps and hopefully get your results. In writing the
procedure, you should number each step; include balanced chemical equations (if a
chemical reaction takes place); include mathematical equations (if used in the
experiment).
10. Equipment setup
In some labs, a labeled diagram should be included with the procedure so that the setup
of the experiment is clear. The drawing should be neat and important equipment and setup instructions labeled.
11. Measurement techniques
The following websites provide information on the proper recording of measurements
using rulers and graduated cylinders.
http://alpha.chem.umb.edu/chemistry/ch117/labs/1LengthVolumeRev.pdf
http://www.chem.tamu.edu/class/fyp/mathrev/mr-sigfg.html
Part Two: Data Collection and Analysis
12. Qualitative Observations
Qualitative observations are those things that your senses pick up; what you see, hear, or
smell during the lab experiment. Observations should be descriptive and written in
complete sentences.
13. Tables
Tables are used for quantitative observations so that data is organized in an orderly
manner. All numeric values should be recorded with the correct level of precision (based
on the measuring equipment) and accuracy. Label all data very clearly and always
include proper units (g, mL, etc.)
14. Graphs
General Guidelines:
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Plot the independent variable on the X-axis. Plot the dependent variable on the Y-axis.
Choose scales for the main divisions on the X-axis and Y-axis. Be sure to use the entire
graphing area. Don’t squeeze a graph in the corner of a piece of paper.
Include these labels on the graph:
Title – ALWAYS title the graph “Y-axis label” vs. “X-axis label”
X-axis label – include NAME of the X-axis and the UNITS of the X-axis
Y-axis label – include NAME of the Y-axis and the UNITS of the Y-axis
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•
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For most graphs, draw the best fit curve through the average of the points, ignore any
points that are obviously erratic (bad data points). DO NOT necessarily connect the first
and last points. DO NOT necessarily go through the origin. DO NOT play connect the
dots!
If a slope is to be calculated, do the work on the paper. Choose two points where the
plotted line crosses an intersection of the grid. Use the equation slope = rise / run.
For some graphs in biology which attempt to show every change in a population, growth,
etc., the data points should be connected. Check with your teacher to determine if you
should draw the “best fit” or simply connect each data point.
Example
Distance vs. Time
60
Distance (meters)
50
40
30
20
10
0
0
2
4
6
8
10
12
Time (seconds)
Click on the following link for guidelines on
Creating Charts in Excel
15. Calculations
You should show how calculations are carried out. Title each of the calculations, write
the original equation and show how you have substituted numbers into the equation.
YOU MUST USE UNITS.
16. Accuracy
Accuracy is a measure of how close an experimental value is to a value which is accepted
as correct. Accuracy is usually reported as absolute error or percent error.
Absolute error = experimental value – accepted value
Percent error = experimental value – accepted value x 100%
Accepted value
For more in-depth analysis of uncertainty and statistics, check the following web sites:
http://www.phys.selu.edu/rhett/plab194/error.html
http://physics.nist.gov/cuu/Uncertainty/index.html
17. Precision
Precision is a measure of the reproducibility of experimental measurements. The quality
of the instrumentation is a major contributor to precision. Precision is reported as
deviation or difference of values.
Absolute deviation = │measured value – mean │
The average deviation is the average of all the absolute deviations.
The percent deviation is the average deviation reported as a percentage:
Percent deviation = average deviation x 100%
mean
Section 3: Conclusions and Evaluations
18. Lab questions
Often the teacher includes several questions with a lab. You should answer in complete
sentences and support your answers with the data from the lab.
19. Conclusion
A well-written conclusion should include the following:
• Summarize and state results.
• State whether there is or is not support for your hypothesis.
• State and discuss specific sources of error. NOTE: Human error and
instrumental error exist in all experiments and should not be listed as a
source of error unless they cause a significant fault.
• Describe the effect of error on numbers or calculations.
• Suggest modification to the procedure.
• Discuss expanded applications.