GENERAL REMARKS ON LABORATORY WORK
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GENERAL REMARKS ON LABORATORY WORK , RECORD KEEPING, AND REPORT WRITING by J.C. de Paula, J.P. Chesick, F.R. Blase, R.C. Scarrow, and T.L. Newirth 1. INTRODUCTION Chemistry is an experimental science and, as such, one cannot appreciate its beauty without spending some time in the laboratory. One of the principal aims of the experiments in this course is to introduce you to experimental physical chemistry. You will learn to use quantitative glassware, electronic balances, computers, and spectrophotometers. You will also be trained in proper record keeping and in the writing of accurate, concise, and informative reports. Another aim is to show you how these basic skills may be applied to the solution of problems of current relevance, particularly those related to biological and environmental aspects of chemistry. In the end, you will have some idea of the difficulties and the painstaking effort involved in gaining reliable scientific results. The keys to successful laboratory work are: safety, preparation, concentration, cleanliness, alertness, and a calm demeanor (even when faced with adversity). You will note that safety was mentioned first. That is because it should be always on your mind from the minute you walk in the laboratory. A sound knowledge of safety rules will eliminate much of the anxiety associated with laboratory work. Let us review the safety guidelines, which we must follow this semester. 2. LABORATORY SAFETY The following rules are designed to help ensure that all work done in the laboratory will be safe for you and your fellow students. No set of rules can cover all possibilities. There is no substitute for watching and thinking about what you are doing. Here are some notes on safety: LABORATORY HOURS. You are expected to come in for laboratory work every Tuesday and Thursday, from 1 pm until about 4 pm. You may not conduct experimental work unless one of the instructors is around to assist and supervise you. Fellow students may not supervise your laboratory work. You may perform computational chores at any time of the day without supervision. Chemistry 302 General Remarks page 2 EYE PROTECTION. Glasses or safety goggles must be worn at all times while in the laboratory. Contact lenses may not be worn because they offer no protection and may trap splashed or splattered liquids, increasing possible eye damage. Safety glasses or goggles may be obtained from the chemistry stockroom in case you do not wear glasses. Any student not wearing eye protection in the laboratory may be dismissed from the laboratory by the instructor. If any chemical comes in contact with the eye, the most effective first aid is the immediate flushing of the eyes with a stream of cold water from a faucet at a sink. SAFETY SHOWERS. Be aware of the location and operation of safety showers. If you or a colleague has a bad chemical spill on clothing or hair, or clothing catches fire from a burner flame, douse yourself or help the person in need to do this in the safety shower. CLOTHING. Bare feet are not allowed in the laboratory because of the occurrence of broken glass and spilled chemicals on the floor. Tops of bare feet are also the most likely recipients of spilled chemicals. With this in mind, it goes without saying that open sandals are also not allowed in the laboratory. In order to prevent contact of corrosive chemicals with the skin, I recommend that you keep as much of your body covered while in the laboratory as possible. A laboratory apron is often an appropriate means of protection for your clothes as well as your skin. PIPETING. Under no circumstances whatsoever are you to pipet by mouth. Most chemicals are highly toxic. Most people will also dribble saliva into the pipet, thus increasing the chance of sample contamination. LABORATORY BENCHES. Never put food down on a laboratory surface, or eat in a laboratory, and always wash your hands thoroughly between doing any laboratory work and eating any food. Apparently clean lab benches may have residues of chemicals (for example invisible mercury droplets from a broken thermometer) which can be picked up by food items. Please do not put your bookbags on the benches for two reasons: (i) you may contaminate it with chemicals that you will then bring home to you and your roommate, and (ii) they occupy valuable workspace. FIRST-AID. Bring any injury (cut, burns, etc.) and spills to the immediate attention of a laboratory instructor. In the interest of providing immediate medical attention to any possible injuries, it is imperative that you never work alone in the laboratory. There should always be another person in the immediate area who is aware of your existence and what you are doing. PROPER BEHAVIOR. It is obvious that horseplay is not allowed in the laboratory. Students engaging in any kind of horseplay will be dismissed promptly from the laboratory. You should never hurry through an experiment, no matter how pressed for time you may think you are. Haste usually leads to bad results or, more importantly, to injury. HOUSEKEEPING. Cleanliness and safety always go together, so we request that you follow these guidelines: Chemistry 302 General Remarks page 3 • Never add reagents to containers while they are on the pans of the analytical balances. Some spillage results in the course of a day, equipment corrodes, the risk of injury increases, and many suffer. • Never return unused chemicals to reagent stock bottles. Be sparing in the amounts you take. Return for more if needed. • Never insert pipets or medicine droppers into reagent bottles to avoid the possibility of contamination of community supplies. Do not lay bottle stoppers down on the bench where the stopper can either pick up impurities or contaminate the bench surface. • Read carefully the label before taking any reagent, and record the concentration on the label; it may not be exactly that suggested in the laboratory directions. • Keep your laboratory bench and communal areas free of clutter and well-organized. This will decrease the risk of spillage, breakage and, consequently, injury. • The person using a piece of equipment is responsible for its cleanliness. If you come to a balance or other piece of equipment and it is messy, either clean it or find the person who left it that way and ask him/her to clean it. Work done with a messy balance or other piece of equipment is evidence of poor laboratory technique. • If you are not familiar with some of the equipment, ask the instructor or an assistant about its proper use. In designing the experimental procedures and the laboratory, we have attempted to minimize the risk of injury. Having laid out a plan for prevention above, let us now describe some guidelines for handling emergencies. EMERGENCY PROCEDURES • Notify the instructor or a fellow student of the accident. If you believe that doing so may delay proper action, then • Take whatever action is necessary to minimize injury to you or others. • While the instructor is tending to the accident, leave the room and encourage your fellow students to do so, as well. • Go to the nearest and safest campus phone and notify the Haverford College Security Department: DIAL 1111 3. PREPARING YOURSELF FOR AN EXPERIMENT By reading and understanding the safety rules above, you have already done much to prepare yourself for laboratory work. The next step is to familiarize yourself thoroughly with the Chemistry 302 General Remarks page 4 specific experimental procedures before you even set foot in the lab. In this course, this means reading and understanding the laboratory handouts prior to the lab period. If you have any questions about the handout, see the instructor as soon as possible or ask questions during the pre-lab discussion. There is no excuse for failing to read the handout before a laboratory period. At least one week before the experiment is to be conducted, the handouts will be available for downloading from the course’s web site (http://www.haverford.edu/chem/302/302.htm). After reading the handout, you will want to write down in your laboratory notebook an outline of the procedures. In doing so, you are saving laboratory time! Instead of leafing through many pages to find out what to do next, all you have to do is glance at a page in your notebook. Because you understand the procedures, you know exactly what is entailed in performing each task in the outline. Your every action is planned out and you can go about acquiring data very efficiently. Some of you will find beauty in efficiency itself, others will relish getting out of lab in as little time as is necessary to obtain good data. Please do not mistake efficiency for haste. If you hurry through a procedure, you are likely to forget important details, or injure yourself (or others). Carry on at a pace that is conducive to good data, and count on your instructor's patience and understanding. 4. THE LABORATORY NOTEBOOK In all scientific activity, it is important that accurate written records be kept. The record must be organized in some way, must be complete, concise, and readable. For this purpose, a bound notebook is customarily used. All entries should go immediately into this notebook. They must not be recorded first on odd scraps of paper and then copied into the notebook. This is poor procedure since it runs the risk that significant information will be lost. Your notebook should be complete enough so that you could go back to it in several years time and be able to re-construct what you did and re-calculate your results. Ideally, someone else familiar with the procedures should be able to do so as well. All raw data should be included: chemicals used, concentrations, weights, volumes of materials added, instruments or volumetric glassware used, etc. Use common sense, however, and do not record trivial information, for example the size of the glove that you are wearing. All observations should be recorded. For example: ".... B was initially colorless. Upon addition of the pale green A, a blue color was noted. Occasionally, white particles were seen, but these disappeared upon stirring. Upon further addition of A, a white precipitate formed..." Be alert for unexpected or incidental phenomena and record these. They can often provide clues as to why an experiment turned out the way it did. Chemistry 302 General Remarks page 5 4.1 GUIDELINES FOR RECORD KEEPING I recommend the following procedures for accurate record keeping in the laboratory. Remember that the better your records, the more complete and impressive your reports will be. • Put your name, address, and phone number on the cover of your notebook. • Leave space at the front for a table of contents. • Number the pages of your notebook. • Enter all pertinent information in detail. Make sure to enter all data and the method by which it was taken. If in doubt about whether or not to record something, record it. If the information is needed at some later time, you will have it. • Enter the type of equipment used, and the manufacturer. • Record the accuracy of any volumetric glassware (e.g., "50 mL buret graduated in 0.1 mL was used"). • In recording data, record only the significant figures. • Date the pages of your notebook. • Cross out discarded data lightly. You may want to read them later. When discarding data, note why you did so. • Label all samples. Feel free to devise your own system. For example, I may label a sample JP-145-B, where JP are my initials, 145 is the page number where the entry was made, and B indicates that this sample supersedes JP-145-A. • Data collection for similar experiments should be arranged in tabular form, if possible. On the following page you will find a sample page of a laboratory notebook, where some of the points outlined above have been used. Please do not hesitate to ask questions about record- keeping procedures if you are not sure about any of the above. Chemistry 302 General Remarks page 6 SAMPLE LABORATORY NOTEBOOK PAGE Page Number: The key to the Date: Important? You’d labeling system! All material labels better believe it! and run labels are referenced to what Page 15 page you’re on! 8/27/98 Experiment #2 - Titration of an Unknown Brief Outline, written before lab, is often helpful, but does Planned Procedure not substitute for later recording what is actually done. 1) Obtain unknown from professor 2) Accurately weigh sample of approx. 0.3 g 3) Dissolve sample in 50 mL water 4) Add indicator 5) Titrate with standard NaOH to pink endpoint Results: A n u n k n o w n w a s o b t a i n e d f r o m t h e p r o f e s s o r a n d l a b e l e d D G - 15 - A. Three samples were weighed out as follows Mistake? Strike out lightly, insert corrections and date it (if made on a S a m p l e D G - 15 - B Gross 0.7029 g later date)! If necessary, note why you made the correction. Remember: Tare is weight of empty Tare 0 . 4 3 2 1 g neatness does not count, but vial, cap, and label.. Net 0.2708 g accuracy and honesty do!! Titration DG - 15 - 1 . S a m p l e D G - 15 - B w a s p l a c e d i n a b e a k e r a n d Three drops of phenolphthalein indicator solution were added. The NaOH (Lot #811-A) with a class B Fisher buret. Starting buret o f p i n k i s a t 2 6 . 7 3 m L ( ± 0 . 0 2 m L ). F u r t h e r a d d i t i o n l e a d s t o Titration DG - 15 - 2 S a m p l e D G - 15 - C was ............ Sample Numbering (your initials -page #- Analysis of Data letter): A label containing this designation is placed on the vessel containing the sample. The sample is instantly identifiable to anyone Analysis and Discussion Sections: reading your notebook (including you). Lot number: Why not do these in your notebook Important in first, as a draft for your lab report? tracking down inconsistencies. Chemistry 302 General Remarks page 7 5. THE LABORATORY REPORT Writing is an integral part of academic life. Hence, it is our goal in this course to develop not only your laboratory skills, but also your language skills, as they apply to scientific writing. Generally, the writing style of a scientific article will differ significantly from styles used in the Humanities and Social Sciences. Some of the practices used in English or History courses do not apply to scientific papers. For example, although clever symbolism may enrich a narrative, the scientist must present all facts pertinent to a result in a logical and unambiguous fashion. Also, scientists use the passive voice almost exclusively. Your English professors will not agree with this practice, but I recommend that you follow it nonetheless. Finally, a laboratory report should not be the product of stream of consciousness. I recommend that you write a draft of your report and that you edit this draft until the discussion is organized and makes sense. 5.1 HONOR CODE REQUIREMENTS Since students are encouraged to work together in the course and often work as partners in the laboratory, many questions arise each year about laboratory reports and the requirements of the Honor Code. The following is an attempt to make clear the faculty member's expectations concerning laboratory reports. Each student is expected to write his/her own laboratory report. Partners may not write one report and submit two copies. Also, all computations and questions asked on the lab handouts should be answered individually. If you consult a literature source, you must give credit to the source (research articles, textbooks, monographs, web sites, etc.). If you consult with a student who has had the course previously or read a laboratory report from a previous year, you must give credit to this source. Your laboratory grade should be based on your work, not that of someone else, so that if you rely heavily on the laboratory report of a student from a previous year, you must expect your laboratory grade to show some reflection of that reliance. The instructor will assume that everything in your report which is not attributed to another source is your work. If you abide by the following, there should be no problems: a. Write your report yourself. b. Give credit to your sources. c. Do your own calculations, and answer questions in your own words. d. When uncertain, consult your instructor. 5.2 REMARKS ON STYLE Here are general points about style: Chemistry 302 General Remarks page 8 • Your laboratory report must be word-processed. The text should conform to the accepted rules of English spelling and grammar. We require that complete sentences be used and that outline format be avoided. • If you know how to use a molecular graphics program, such as ChemDraw, please feel free to use it as appropriate. However, structures and mechanisms may be hand- drawn. • We strongly encourage you to use Microsoft Word's symbol font and equation editor. However, equations and symbols may be hand-drawn. Please do not attempt to substitute an odd collection of characters for a symbol. For example: (i) /_\ and D are not appropriate substitutes for ∆; and (ii) the notation 1.0E-5 is not to be used instead of the correct 1.0 x 10-5. • The main point of a scientific report is to describe the results and discuss the conclusions of a set of experiments. You should use your own words to convey the message. Direct quotations from textbooks, monographs, or other journal articles are not permitted. • The laboratory report for this course should describe the results and conclusions in enough detail that any reasonably well-educated chemist off the street can understand. It should not contain cryptic references to handouts or lecture notes. Yet, the report should be concise; in the context of our course, any laboratory report exceeding fifteen pages of text is probably too long. • For general formatting of the report, and for proper use of scientific language, we suggest that you follow the guidelines put forth by the American Chemical Society. These may be found in the ACS Style Guide, which will be placed on reserve in Stokes Library. If the Guide does not answer your questions, then consult one of the instructors or ACS publications, such as the Journal of the American Chemical Society. • Your report should be divided into sections: title, abstract, introduction, experimental section, results, discussion, acknowledgments, and references. These are discussed in detail below. TITLE. The ideal title consists of one sentence describing the system and/or technique you studied. Example: "Chymotrypsin: Catalytic Efficiency and Thermodynamic Stability" is a viable title for a report on the first project in the course. Immediately below the title, the names of all authors should be given. Co-authors are those persons who contributed significantly to the experimental work and interpretation of results. For the purposes of our course, each student should submit his or her own lab report. The by-line should show the writer's name first, followed by an asterisk; the names of collaborators should follow immediately. Example: Spectroscopy of the Sun Marie Curie* and Gerhard Herzberg Chemistry 302b, Haverford College Chemistry 302 General Remarks page 9 In the preceding example, Curie and Herzberg worked together on the experiment, but Curie wrote the report. Herzberg should turn in a separate report, where his name appears first, with the asterisk. Minor contributors should be acknowledged at the end of the article (see below). Use your best judgment and the honor code guidelines in deciding whose name goes on the title page; if in doubt, ask the instructor. ABSTRACT. The abstract is a very concise summary (no more than two moderately sized paragraphs) of the experiment, including methods, important results, and conclusions. In principle, the reader should have a clear idea of what you did by just reading the abstract. To achieve this effect, avoid references to the main body of the report ("...The data in Figure 2 show that the entropy of the Universe is indeed increasing...."). Even though it appears before the main body of the paper, the abstract is the last part of the report to be written. As a summary, the abstract should contain no insights and conclusions that are not developed in the main body of the report. INTRODUCTION. In this section, you are to provide the reader with brief background information on the system that you studied. More importantly, you should state clearly the purpose of the experiment. This is the first section where literature citations may be necessary. The Introduction is a good place to define reactions, equations, abbreviations, and terms that will be used throughout the report. Again, avoid jargon specific to handouts because they would not be understood by a reader who is not taking the course. EXPERIMENTAL SECTION. You should include a detailed account of your experimental procedure; that is, what you did in the laboratory and how you did it. Observations are also important. For example, if a reaction began to heat up upon addition of a reagent, then report the observation. If you performed a procedure exactly as described in a handout or in the literature, then you need only provide the reference. Any deviation from a given procedure must be described in detail. The assumption is that any procedure for which no literature reference is given is one that you developed yourself. If you do not give proper credit, you are guilty of plagiarism. Do not be afraid to credit the suggestions and ideas of your classmates. You will always gain - rather than lose - respect by adhering to this policy. When describing a new or modified procedure, provide enough detail so that anyone with background similar to yours can repeat the work without rediscovering what you have already uncovered. Avoid outline format when describing your procedures. Be sure to include in your text: • the supplier and purity of your reagents; • the volumes, masses, and moles of your reagents; • methods of sample preparation (e.g., anaerobic, low or high temperature, etc.); • manufacturer and model number of commercial instruments; Chemistry 302 General Remarks page 10 • a block diagram and a brief description of the main components of any home-built instrumentation ; • the mass, number of moles, percent yield, m.p. or b.p (where appropriate) of your products; • the literature values of m.p. or b.p. for a product, if it has been prepared in the past by the same or a different method. RESULTS. This is the most important part of your report. Your results must be shown succinctly and clearly, so that the reader can evaluate the quality of your work and the validity of your conclusions. Here are a few suggestions to help you in this task: • Use figures (which may contain structures, graphs, spectra, schematic views of instrumentation, etc.) and tables whenever possible. • Tables and figures are to be numbered for reference in the discussion. They should be given titles and legends. The legend should identify the sample, method of detection, and experimental conditions (temperature, power, resolution, etc.). The axes of graphs and spectra should be labeled clearly, with the appropriate units. • You should describe in words the key features summarized in the figures and tables. If you have a negative result, it is unnecessary to go into great detail. Simply summarize failed attempts so that the reader will know what to avoid. • You should analyze spectral data in detail. Obviously, the tenor and depth of the analysis will depend on the type of data and the purpose of the experiment. We will give you specific guidance on this in the upcoming handouts. • Raw data should not be presented. Data are presented far more effectively after processing in tabular or graphical forms. But, you may ask, what are raw data? • Example: suppose that you obtained the absorption spectra of a compound in twenty different solvents. The spectra are similar in shape, but the wavelengths for maximum absorption depend on the solvent. You decided to present your data by attaching all twenty spectra to the report, marking the position of the absorption maxima on each one. Consequently, the reader must leaf through twenty pages of data, only to extract one number from each page. The same data could be presented more effectively by showing a table of solvents used and the corresponding wavelengths for maximum absorption. The remaining spectra should be stored carefully in you laboratory notebook. • Example: suppose that you obtained two hundred pH readings for a titration of an aminoacid with a standard NaOH solution. Subsequently, you analyzed the data by a least squares method and obtained a list of calculated pH values that fit the experimental data. When presenting these data in your report, you should not provide a long list of experimental and calculated pH values versus volume of NaOH solution added. Instead, you should display the data in graphical form, as a titration curve, where both the experimental data points and calculated curve are displayed simultaneously. • If appropriate, include a full-blown sample calculation in the results section, showing the relevant equations. If the calculations were performed with a computer, then show the Chemistry 302 General Remarks page 11 pertinent equation and state what kind of hardware and software were used. Pay special attention to units. DISCUSSION. In the discussion section, you should elaborate on the meaning of your data, explaining the behavior of your system with sensible scientific arguments that can be substantiated by literature citations. You should also discuss sources of errors, low or high yields, suggest improvements of experimental design, and answer questions posed in the lab handout. You may also make hypotheses based on your results and propose experiments that can test the hypotheses. Here are some additional guidelines: • It is possible to combine the Results and Discussion sections into a single section. Please ask one of us first before doing this. • Avoid rephrasing statements that were already made elsewhere in the report. • Avoid statements such as: "There is the possibility that bad laboratory technique or that a badly calibrated instrument led to errors". In a way, this is always implied; however, unless you can identify exactly how your technique or the instrument was flawed, the statement is not very useful because it is not specific. If indeed you can identify the flaw, then you should not submit a report on the experiment. Rather, you should repeat the experiment with an eye toward preventing the problem. • Avoid "fillers" like "I learned a lot of chemistry from this experiment" or "This was the experiment from hell". We will provide other vehicles for your praise and dissatisfaction: course evaluations! CONCLUSIONS. After interpreting your results, you will reach certain conclusions about your experiment. In many cases, these conclusions were already included in the Discussion section. If you wish, you may state them in a separate Conclusions section. Avoid repeating yourself, though! ACKNOWLEDGMENTS. You should acknowledge minor contributions to experimental work or data interpretation, as required by the Honor Code. REFERENCES. The section on Honor Code requirements states clearly our policy on literature citations. Consult the instructor if in doubt as to what requires a citation. The References section (also referred to as the Literature Cited section in some journals) is a very important part of your report. Among other things, references show the reader that you have studied the literature and have found precedents for your arguments there. Also, it makes people very mad when they are not cited for their work! Let us begin by discussing the differences between bibliography, literature citations, and footnotes. In scientific papers, only the latter two are to be used. Researchers in the Humanities and the Social Sciences end their papers or books with a bibliography: a list of their sources of information. Throughout the work, footnotes point to specific chapters or pages of items listed in the bibliography, from which information was extracted. Footnotes are also used to elaborate on a point developed in the text. This is not how referencing is done in scientific papers. Chemistry 302 General Remarks page 12 Each scientific journal handles references in slightly different ways. One common link in all of the accepted formats is the absence of the combined use of bibliographies and footnotes. We will follow the style proposed by the editorial board of the scientific journal Journal of the American Chemical Society. The ACS Style Guide is another source of information on this subject. A reference is a journal article, a chapter in a book, or even an entire book. Each reference is given a number; the numbering reflects the order of appearance of the reference in the text. Every time you feel that a statement must be referenced, you should follow it with the appropriate reference number in parentheses. For example, The rate of electron transfer between Ru(II) tris(bipyridyl) and Fe(III) in 0.1 N HCl was obtained by the time-resolved fluorescence method of Lind et al. (1). These rates agreed to within 1.0 % with those obtained by flash photolysis studies (2). Here, a paper by Lind et al., is used as a reference for the experimental procedure. This paper is the first reference of the report, so that it carries the number 1. Subsequent citations carry different numbers. If you cite the same paper several times in your report, you should use the same reference number for that paper. For example: The rate of electron transfer between Ru(II) tris(bipyridyl) and Fe(III) in 0.1 N HCl was obtained by the time-resolved fluorescence method of Lind et al. (1). These rates agreed to within 1.0 % with those obtained by flash photolysis studies (2). Thus, our studies confirm the accuracy of the fluorescence technique, which was not assessed previously by Lind and coworkers (1). It is not necessary to point to a specific point of the article or book chapter when referencing it. For example, you want to reference two rate constants from an article by Curie and Herzberg. The first number appeared on page 543 and the second on page 567. Instead of using two distinct reference numbers for this article, one for each page number where the information is found, you should reference the entire article both times, thus using only one reference number. At the end of the report, a separate section, entitled References or Literature Cited, will list the references in increasing numerical order. You should give the reader unambiguous information about the cited work so that it can be found easily. A journal article should be referenced as follows: Yang, Y.-M.; Fales, H.M.; Pannell, L.K. Anal. Chem. 1985, 57, 1771-1772. Chemistry 302 General Remarks page 13 The names of the authors (last name first, then initials) are followed by the abbreviated name of the journal, the year of publication, the volume number, and the page numbers of the article. An article appearing in a book edited by a second party is referenced as: Schwartz, H.; Schiebel, H.M. in Chemistry of the Peroxides; Patai, S., Ed.; Wiley: Chichester, U.K., 1983; pp. 105-127. The names of the authors are followed by the book title, the editor's name, the name and location of the publisher, the year of publication, and the page numbers. A chapter in a textbook or monograph would be referenced as in the following two examples: Voet, D.; Voet, J.G. Biochemistry; Wiley: New York, 1990; Chapter 20. de Paula, J.C. Chymotrypsin: Catalytic Efficiency and Mechanism of Action; Haverford College: 1999. Scientific articles do use footnotes occasionally. They are reserved for parenthetic statements that explain further a point brought up in the text. By separating a statement from the main body of the text, the author can prevent disruption of the flow of logic. Most journals, such as Journal of the American Chemical Society, treat footnotes and references equally, listing them together at the end of the article. Please do not hesitate to ask questions about reference formats if the discussion above seems nebulous. We are here to help! Have fun and good luck!