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experiment guide 1-3

experiment guide 1-3 - CHEM 6BL Experiments 1-3 Guide...

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CHEM 6BL Experiments 1-3 Guide Page 1 of 7 EXPERIMENT #1 GUIDE This guide contains a list of laboratory procedures, laboratory report hints, and some of the common lab-specific questions often asked by students in this course. The identity of the author(s) of any new questions posted will remain anonymous. However, I reserve the right to modify any of the questions in order to provide clarity to the reader. Lab Procedure : Be sure you write down your Unknown Solution ID # . You will need this information to ID your unknown concentration in your Abstract , Results & Discussion . In this experiment, one of the common problems is to obtain too little or too much precipitate , leading to a calculated concentration of [Al 3+ ] that is either too low or too high ! Be sure that you have precipitated ALL of your possible Al(Ox) 3 (aka. Alq 3 ) and that you have done the experimental procedure correctly so that you will generate the maximum amount of precipitate. Also make sure you have fully dried your precipitate products in order to avoid overestimating [Al 3+ ]. It is now believed that the most likely causes for obtaining too little or too much precipitate are: 1) the p H is still out of balance ( e.g., too little acetate buffer has been added ), so CHECK YOUR p H and add more buffer if necessary, or 2) your product is still wet , so make certain you have fully dried your product! Lab Report : Experiment #1 uses a worksheet . Read the worksheet carefully so that you know which sections need to be written up in your lab notebook and which sections are written into the worksheet directly. Accuracy: 10 points ( -1 point for each ±5% away from the actual concentration of the unknown [Al 3+ ] solution). The Introduction section needs to be hand-written into your lab notebook. In the Introduction , make certain you talk about OxH vs. Ox ! Also include all relevant chemical & math formulas. The Results section includes Data , Observations and Calculations , all of which are written directly into the worksheet . Calculate [Al 3+ ] for all three trials in the space provided on the worksheet, then take the average and figure out 2× the standard deviation (i.e., 2 σ ). In your Discussion (also hand-written into your lab notebook), discuss any excluded trials (Q-Test?!?) as well as the relative size of your standard deviation (2 σ ). Also discuss any (general) potential sources of error even if you didn't encounter them!
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CHEM 6BL Experiments 1-3 Guide Page 2 of 7 : In Experiment #1 , I think that two of my data values are pretty much right (they are close to each other), but I think the third datum of mine is wrong. Should I throw it out? No. If you have the time, do more precipitation trials.
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