Writing an Effective Lab Report

The Importance of the AP Laboratory Notebook Demonstrates the quality of the laboratory work you have done. You will most likely need to show your notebook to the Chemistry Department at the university you attend in order to obtain credit for the laboratory part of your AP Chemistry course. Someone who is unfamiliar with your work will be using your notebook to evaluate your laboratory experience, so be sure you are CLEAR and CONCISE.

The Notebook On the inside front cover, list identifying information. Begin a Table of Contents that you will add onto with each lab you perform. Include the experiment number, title, and the page on which the lab begins in your notebook.

The Notebook (cont.) Write in blue or black ink only! Lab reports are written on the front of the pages only. The backs may be used for scratch work and notes. No erasures or white-out may be used. Draw a single line through any errors. DO NOT scribble out! Do not remove pages from the lab book (except the carbon copies for turn in). Insert the periodic table card stock under the copy page before writing.

The Lab Report Pre-Lab Post-Lab The lab portion of this class is worth 35% of your overall grade. In order to earn a good grade in AP Chemistry, you must master the art of writing a lab report. Lab reports are to be written individually. Copying will result in a loss of credit by both parties involved. Your lab report is to include the following sections: Title Purpose Introduction Procedure Data Table(s) Calculations Graphs Questions Conclusion Pre-Lab Post-Lab

Title The experiment number, experiment title, date of the experiment, your name, your lab partner's name, and the course name and period number should be written in the title box on EVERY page of the lab. I will check that the title boxes are completed on every page of the pre-lab as well as checking when I grade your overall lab report.

Purpose The Purpose is a brief one or two sentence explanation of what is to be accomplished in the lab. It should be in your own words, NOT copied from the lab handout!

Introduction Give a general overview of the chemical concepts investigated in the lab. By what means will the purpose be achieved? All chemical equations and important mathematical formulas should be included in this section.

Procedure You will not have access to the lab handout in the lab, so you must rely on your own written procedure in your lab notebook. Should be written in a numbered list. DO NOT copy verbatim from the lab handout. You should summarize the steps in your own words. Points will be deducted for verbatim copying. The goal is to become familiar with and understand the procedure, thus eliminating costly errors in the lab and wasted lab time.

Data Table(s) Data tables must be constructed prior to lab and filled in as the experiment progresses (not copied from a lab partner or from jotted notes after). Data tables must be drawn with a ruler. If a data table(s) is not given to you on the lab handout, you must construct your own. Remember, not all data lends itself to tabular form. Sometimes, labels and blanks are more effective. Data must be entered with the appropriate number of significant figures and include a unit.

Calculations If applicable, number each calculation to match the lab handout. You should show how calculations are carried out. Equations should be written separately before numerical substitutions are made. LABEL each value with units and identification of what it represents. For a series of calculations using the same process (such as in multiple trials), show only a sample calculation. If a results table is requested in the lab handout, it should be included in this section.

Calculation Examples Calculation shown for Trial 1, only answer listed for Trial 2. Every value is labeled with what it represents. Equation written separately and then numerical substitution is shown.

Graphs This section will not be in every lab. When graphs are required, they should be drawn before you leave the lab session so that you can verify the quality of your data and rerun experiments if necessary. Graphs should take up the majority of the page and axes should be scaled appropriately to fill the graph space. Be sure to include a graph title and axes labels!

Questions Questions that are asked of you in the lab handout that are not calculation based should be answered in this section. Number answers to match the question numbers from the handout. Restate the question as part of your answer and answer in complete sentences. Be sure you answer all parts of the question!

Conclusion This section is a thorough discussion of the results of the experiment, written in the third person. If applicable, include averages, percent error, and standard deviation in your discussion. The conclusion should readdress the purpose of the experiment. Results should be summarized and their accuracy discussed. Were the scientific concepts involved accurately reflected (why or why not)? What theory was demonstrated in the experiment?

Conclusion (cont.): Error Analysis Your conclusion should include an error analysis discussion. An error analysis looks at possible experimental errors within the lab that could account for the data's deviation from expected (or literature) values. You must list at least TWO experimental errors that could explain your results unless otherwise told. NOTE: Instrumental error and human error exist in all experiments and should not be mentioned as a source of error unless they cause a significant fault. Even so, they DO NOT count as one of the required two sources of error. Sig Figs and calculation errors are NOT experimental errors.

Thinking of Experimental Errors First, was your result higher or lower than the expected or literature value? Look at the calculation you performed to obtain your result. How would the numbers involved have to be “off” in order to get a too high/too low answer? This value is higher than the expected 22.4 L/mol. To get an answer that is too high, either the numerator had to be too high or the denominator had to be too low (or both).

Thinking of Experimental Errors (cont.) What could have caused the numbers to be “off” in such a way? The numerator represents the volume of hydrogen. What could make that volume too high? One hint for finding experimental errors is to look for complicated steps in the procedure that might be near impossible to perform perfectly. The volume of hydrogen could be too high if air leaked into the eudiometer during the somewhat complicated “inversion” procedure called for in the lab. The denominator represents the moles of hydrogen which was calculated stoichiometrically based on the starting length of the magnesium piece. Since measurement errors are not experimental errors, we will assume we measured the length of the piece correctly. So how might we have still obtained a too low value for the moles of hydrogen? Another hint for finding experimental errors is to look for any assumptions, generalizations, or shortcuts the procedure may have called for in the experiment. One such generalization is that the magnesium ribbon maintains a 0.0094 g/cm length ratio over the length of the entire ribbon.