How to Write a Lab Report

Transcription

1 How to Write a Lab Report Each section of your report should be clearly identified. Reports must be done on the computer. If you do not have access to a computer at home, you will have to use the computers at school. Each section must have the section name. Lab reports should be written in a neutral voice (do not write I or we did something ) The following sections must be included. 1. Lab Report Title - The title should include a description of the experiment that was performed. Good Example: Title: Effect of Photoelectric Cells on Battery Life Bad Example: Title: Lab Report 2. Write a Hypothesis or the Objective to the Lab Hypothesis - A hypothesis should describe what you think is going to happen in your experiment. Many times a hypothesis is in the form of an If/Then statement. You will generate your hypothesis before you perform the lab. A hypothesis is written in the form of a statement that can be proved true or false. (One to two sentences maximum.) Good Example: Hypothesis: The combined masses of all the reactants that are mixed together to cause a reaction will equal the masses of all the products after the reaction has completed. Bad Example: Hypothesis: I think that when I put chemicals together in my experiment they are going to weigh the same. Note about the Bad Example : It uses I which is not a neutral voice. It is not specific (i.e. which chemicals?). It is unclear (i.e. the hypothesis says the chemicals will weigh the same. But the same as what?) Objective - In many of our experiments, we will be observing chemical reactions. In this case, we will have an objective instead. For most cases, the objective will be given to you either by your instructor or in the lab procedure handout. It is acceptable to write the objective exactly as written from the lab handout. 3. Basis or Background

2 Basis - A basis is used when your lab was designed with a hypothesis. A basis is WHY you think your hypothesis is valid. Describe what scientific principle would make your hypothesis correct. (minimum 1 or 2 sentences) Good Example: Basis: According to the Law of Conservation of Matter, no matter is ever created or destroyed. Therefore, the masses of the initial chemicals used in a reaction should equal the masses of the substances that are produced because nothing would be created or destroyed in the reaction. Bad Example: Basis: I think that the chemicals I mix together are not going to weigh the same because after I put them together because bubbles are going to come off in the reaction. Note about the Bad Example : It uses I which is not a neutral voice. There is no scientific principle stated. The Good example refers to the Law of Conservation of Matter which is a scientific principle. Background - A background is used when you are given an objective. In many cases, a background is given in the lab procedure. It explains some of the scientific principles or ideas behind the lab. In your lab report you need to summarize or paraphrase the background information from the lab procedure. DO NOT COPY the background information. When you paraphrase the background information it is an indication of your understanding of the scientific principles. 4.. Materials List Include a list of materials used for your lab. List only lab related equipment. Be specific Good Example: Bad Example: Materials List: 100 ml beaker Electronic Scale Vinegar Baking Soda Watchglass Graduated Cylinder Materials List: Beaker Electronic Scale Vinegar Baking Soda Watchglass Graduated Cylinder Paper Pen Note about the Bad Example : This lists paper and pens which are not pieces of lab equipment. It also could be more specific.

3 5. Describe your Procedure - This should be a brief general description of what you did in your experiment. It should be in sufficient detail so that the reader understands how you went about proving or disproving your hypothesis or meeting your lab objective. It should NOT be however, a list of detailed steps or a repeating the steps included in the lab instructions. This should NOT be copied from your lab procedure but it should contain a reference to your lab procedure. The lab procedure should be in past tense since it describes what WAS done in your experiment. (Minimum 3 sentences) Good Example: Procedure: In this experiment powders from various mystery sources were used to test solubility, reactions to starch, reactions to hydrochloric acid and reactions to acid/base indicators. The results were compared to known substances in order to identify the unknown substances. Refer to A-15 Mystery Powders Lab Procedure, Rhineholt and Winston Lab Manual, 1990 for a complete detailed procedure. Bad Example: Procedure: First we measured 50 ml of water and placed it into a beaker. We then weighed the beaker and the water. Then we measured our unknown and placed it on a piece of weigh paper. Next we mixed 67 ml of Sulfuric Acid and observed the reaction between the unknown and the sulfuric acid which produced bubbles. Finally we cleaned up our work area and put the chemicals away. Another Bad Example: Procedure: 1. Weighed out 3.2 g of baking soda using the electronic scale 2. Measured 4.5 ml of HCL in a 10 ml graduated cylinder and placed on a watchplate 3. Mixed baking soda with the HCL observing the reaction. Note about the Bad Examples : The first procedure is too detailed. It also includes some observations which should not be in the lab procedure. It does not use a neutral voice by referring to we throughout. Also, it doesn t refer to the detailed procedure used to actually perform the experiment. The second example, lists specific steps. It is too detailed as well. It too does not reference the actual lab procedure.

4 6. Data and Observations - A summary of your data should be included usually in the form of a table. If you had any special starting conditions they should be noted. Usually a data table is suggested in your lab instructions. The table should have a title describing what it contains. QUALTIATIVE data are non numerical observations. QUANTITATIVE data (measurements) should have engineering units for each measurement and an uncertainty factor. Good QUALITATIVE Data Table Example: Data Table: Mystery Substances Test Results Substance Results of HCL Test Reaction to Iodine Soluble? Acid/Base ph Mystery # 1 No reaction Blue Yes 7 Mystery # 2 Fizzed Gold No 9 All tests were performed at 76 degrees C. Good QUANTITATIVE Data Table Example: Data Table: Mystery Substances Measurements Substance Mass (in grams) +/-.01g Temperature (degrees C) +/-.1 o C Mystery # g 76.1 o C Mystery # g 75.2 o C Bad QUALITATIVE Data Table Example: Substance HCL Test Iodine Solubility Acid/Base Mystery # 1 No reaction Blue Yes 7 Mystery # 2 Fizzed Gold No 9 Note about the Bad Examples : No title. Column headings are unclear. Bad QUANTITATIVE Data Table Example: Data Table: Mystery Data Table Substance Mass Temperature Mystery # Mystery #

5 Note about the Bad Example : Title is unclear and too general. Column headings are unclear. No engineering units. No uncertainties given. 7. Data Analysis - This paragraph is where you will comment on your data. You will discuss trends or generalizations in your data along with a clear indication of how your hypothesis is being shown that it is true or false or how your lab objective is being met. If you recorded any data, which you did not use because of error, contamination or possible procedural problems, it should be noted here. ( Minimum 3 sentences) Note: This section will always be discussed in class after each lab. Special requirements for this section will be given for each lab. Refer to special handouts for each individual lab. Good Example: Analysis: The data showed a trend of lower temperatures when exposed to the mystery substance. Also, the red liquids all turned blue and all of the yellow substances became clear. It is important to note however, that the red liquids may have been contaminated because the bottle of hydrochloric acid was spilled during the experiment. This may have caused some hydrochloric acid to have been accidentally introduced into to the red liquids. Bad Example: Analysis: My data showed a trend of lower temperatures when exposed to the mystery substance. Also, the red liquids all turned blue and all of the yellow substances became clear. The red liquids may have been contaminated because the window blew over my bottle of hydrochloric acid during my experiment. Note about the Bad Example : Not in a neutral voice uses my data. It is not clear how the spilled hydrochloric acid affected the results. 8. Conclusions - This paragraph should be a summary of whether you proved or disproved your hypothesis or met your lab objective. You will refer to your hypothesis or objective in this section. Good Example Bad Example Conclusion: The hypothesis that girls are more attracted to boys in 7th grade is confirmed by my data because a greater percentage of 7 th girls stated that they were attracted to boys than in any other grade. Conclusion: This lab was a good lab and it helped me understand the Law of Conservation of Mass. Note about the Bad Example : Not in a neutral voice uses me. It is not refer to the hypothesis and does not indicate if the hypothesis is proved or disproved.

6 9. Possible Sources of Error This section contains your opinion on what possible errors affected your data. Only errors that caused your data to be incorrect are to be noted here. (2-4 sentences) Good Example: Possible Sources of Error: The data collected may have the following errors. The weight of the jar # 5 seems to be incorrect because the data is not consistent with the other data. Every other weight is increasing except data point number 5. It is possible that the scale was knocked during the measurement. Bad Example: Possible Sources of Error: When I weighed my baking soda, I forgot to zero the scale. Then I realized what I had done and weighed it again. Note about the Bad Example : If you know that an error occurred but then corrected it, you should not consider it to be an error. Also, this error statement is not in a neutral voice. The following are NEVER errors: I calculated wrong The scale wasn t working I didn t measure correctly The scale was off The scale wasn t zeroed The scale is not exact. 10. Submittal Requirements A hard copy of the lab report will be handed in on the due date. All lab reports must be typed. Late lab assignments are penalized 10% per day for late work. This penalty is taken AFTER the assignment is graded. (This means if you earned 80 points out of 100, you would receive 72 points after the first day, 64 points the second day, etc.). After the 5 th day, work is worth 50% of your original grade no matter how late it is. However, no lab reports will be accepted past the unit test in which it was assigned. Lab reports make up a significant part of your grade. It is always in your best interest to hand in a lab report even if it is late. Lab Reports can be submitted early for a draft review if requested. Draft lab reports with edits must be submitted along with the final Lab Report.

7 11. Sample Rubric - A sample rubric is attached. Vocabulary Words Useful for Lab Reports Don t Use Dump Exact Fix Gone up Got to complete Gotten rid of, Get rid of Like it should have been Numbers Re-do Should not have happened Thrown Off We came up with We saw Weight Weighed Wrong Use place, discard, pour imprecise, inaccurate **See below change, correct increased completed eliminated as expected measurements, values Be specific the formula - the final mass - the initial mass perform again not as expected was affected, increased, decreased, caused an error indicated by the data indicated by the data mass measured mass incorrect, inaccurate, imprecise Do not use contractions in lab reports. Use do not, can not, etc. ** Remember a measurement is is INACCURATE if the measurement cannot be repeated and a similar amount is measured again (like the first time I measure I measure 6 grams and the 2 nd time I measure, I measure 92 grams!) **A measurement is IMPRECISE if the measurement is not measured to a meaningful measurement scale (like you measure.1 g instead of.17 g)