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: • • • 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 • • • 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.