Remedies for Common Laboratory Ailments

Transcription

1 Remedies for Common Laboratory Ailments Cindy Graham Brittain, Ph.D. Why do you need a Chemistry Lab? As a student of the allied health, environmental, biological, or textile sciences, you might question the need to participate in a chemistry lab course. You haven t chosen a career in CHEMISTRY! So why are you being asked to conduct chemistry experiments and write lab reports? Isn t it enough to learn about chemistry by attending lecture, reading the textbook, and solving problems? But you ll come to discover that there are a number of very compelling reasons why the chemistry lab experience will be an essential part of your learning: Chemistry is an experimental science. The discoveries you make in lab will help you to appreciate that the information in your textbook comes from a combination of inspired reasoning and careful, extensive experimentation. Chemistry will literally come alive for you in the laboratory. Your textbook is filled with photographs and drawings of chemical substances and their reactions; these illustrations are designed to help you understand the concepts presented by your lecture professor. But the laboratory is a living, moving, three-dimensional illustration of chemistry, and you re at the very center of it! When conducting experiments, you ve got the opportunity to see, hear, and perhaps even smell and touch chemistry IN ACTION! A lecture concept that may have seemed beyond your grasp can become self-evident when you see it illustrated in the lab. Experimentation in the lab will help you to develop important skills in making measurements and observations, interpreting your results, and communicating your findings with others. The lab provides the opportunity for you to interact closely with other students in the course. You ll share in one another s successes and frustrations, learn together from each shared experience, and develop a camaraderie that will continue outside the lab (and which may prove to be essential to your success in the course). Anticipate and Prepare for your Laboratory Experience Students are rarely indifferent about working in a chemistry lab. In fact, their emotional reactions to the lab experience can be as varied as the chemical reactions that they re studying. At one end of the scale are the students who look forward to each session in the lab. They eagerly anticipate the challenges they ll meet and the discoveries they ll make. These students enjoy conducting the experiments. They re aware of the safety considerations of the equipment and chemicals, and they take the necessary precautions. They think as they work, and they make predictions about the outcome. They re able to anticipate problems that might arise, and they re ready to suggest potential solutions to those problems. At the other extreme are the students who dread the laboratory experience and approach each session with increasing anxiety. These students work timidly through the experiments, worrying that they ll make a mistake and that the experiment will fail. They may even fear coming into contact with the chemicals. They focus on simply completing each step of the procedure, without giving much thought to the purpose of those steps. They don t attempt to interpret their observations or results while they re still in the lab. And when problems arise, they feel frustrated and helpless. C. Graham Brittain Page 1 of 12 8/31/2008

2 These very different emotional reactions are NOT AT ALL the result of differences in the students natural intellect or ability. Instead, they re the result of a profound difference in how effectively these students have dealt with their anticipation of the laboratory experience. Both types of students anticipate that they will encounter challenges, difficulties, and uncertainties in the lab. The confident and eager students have dealt with this anticipation by PREPARING both emotionally and intellectually for the experience. These students have thoroughly studied the experimental theory and procedure; they ve thought about what they need to accomplish in lab and how they re going to do it. In contrast, the anxious students have NOT dealt as effectively with their anticipation. Because these students haven t emotionally prepared to perform the experiment, their increasing anxiety hinders their attempt to prepare intellectually. The result is that these students are defeated before ever starting the experiment. Clearly these descriptions depict students at the very opposite ends of the scale; your own experience is likely to be somewhere in between. My hope is that you ll become more and more like the confident student with each experiment you perform. The discussion that follows is intended to help you learn to deal effectively with your anticipation of working in the chemistry lab. You have my promise that your lab experience will be both rewarding and enjoyable IF you re able to anticipate the challenges you ll face and then PREPARE, both emotionally and intellectually, to meet those challenges. Here are some challenges you need to anticipate: You ll have difficulty using certain equipment or learning a particular technique. Your experimental write-ups will describe a number of standard laboratory procedures. These include reading the volume of a liquid in a graduated cylinder or buret, using a balance to measure the mass of a substance, or separating a mixture by filtration. Your lab instructor will demonstrate these procedures for you when the need arises. But even with advance study and preparation, it s usually difficult to perform a new technique or use an unfamiliar instrument correctly the very first time. So you should anticipate that you ll feel clumsy and awkward in the lab, just as you would on your first day in a new job. But with time and practice, you ll become comfortable with the new procedures and confident that you can perform them correctly. Some periods of time will be spent waiting. During many experiments, you ll have to wait to use a hood or a balance, to have access to the chemicals needed for a reaction, or to observe and measure a physical or chemical change. You may start to feel bored, and you ll be tempted to conclude that much of the lab time is being wasted by waiting IF you haven t anticipated these moments and prepared to use them to the greatest effect. Making productive use of these waiting periods is often critically important to the successful completion of the experiment. Instead of just standing by or engaging in casual conversation with other students, you and your partner can be asking your lab instructor questions, planning your strategy for the rest of the experiment, washing the glassware needed for the next procedure, reviewing your earlier measurements and observations, or starting to calculate and interpret your results. Something will go wrong with your experiment. In spite of your very best efforts to prepare, sometimes things will go wrong in the laboratory: A beaker may shatter as you re washing it, or a reaction that seemed quite simple may not give the expected result. Sometimes these incidents may be the consequence of a mistake that you ve made: the reaction didn t work because the wrong chemicals were used (you didn t read the label on the bottle very carefully), or the C. Graham Brittain Page 2 of 12 8/31/2008

3 correct chemicals were used but in the wrong proportions (you didn t follow the procedure exactly or misread the mass or volume). But sometimes the incident has nothing at all to do with you! It may simply be the result of lab equipment that failed at a critical moment, or of a chemical that exceeded its shelf-life. When something goes wrong, DON T immediately assume that you ve made a clumsy or careless error. But you should also NOT jump to the conclusion that the experimental procedure, lab equipment, or chemical reagents are in some way wrong. The goal in this situation is NOT to assign blame to anything or anyone, but to work closely with your lab partner and instructor to first try to determine what went wrong, and then to fix it. You should examine the equipment closely, and then attempt the procedure or reaction a second (or even a third) time. If you do find that you made a mistake, you should seize the opportunity to learn from that mistake, so that you don t repeat it in the future. But if the error is with the equipment or chemicals provided, your lab instructor will replace these for you as quickly as possible. If you haven t effectively anticipated these moments and prepared yourself emotionally to deal with them, you may find that your anxiety is rising or your temper is getting short. But if you ve anticipated and prepared, you ll be able to calmly, patiently, and effectively work with your partner and lab instructor to solve any problem that arises. Effective Ways to Prepare for your Laboratory Experience As you can see, it s essential that you come to lab fully prepared to conduct each experiment. Anticipating the situations I ve described above will help in your emotional preparation. However, each and every experiment will also require some thorough intellectual preparation. I ve designed two activities to encourage and to help you with your intellectual preparation: 1. The Pre-Lab Study Assignment Part One of your preparation process is to complete the Pre-Lab Study Assignment. This assignment will vary from week to week, depending on the nature of the experiment. The particular details will be provided as each week s experiment is posted on the course website. For example, for some experiments, you may be asked to complete an online tutorial or watch an online video. But there will also be a written aspect to your pre-lab study. For each experiment, you ll need to print out and complete the posted set of Pre-Lab Questions. Your lab instructor will ask you to hand in your answers to these questions immediately upon your arrival at the lab. If you do NOT have your finished work ready to turn in, you will forfeit your opportunity to perform that day s experiment. If this consequence seems harsh to you, let me explain why it s necessary: In any chemistry lab, safety is the primary focus, and comes before everything else! No experiment or letter grade is more important than the safety of the students in the laboratory! For this reason, a conscientious instructor cannot possibly permit unprepared students to work in the lab, as these individuals could be at risk of harming themselves and others. You must demonstrate your knowledge of the experiment, and particularly, your understanding of its safety considerations, by completing and submitting the required Pre-Lab Questions at the start of each lab period. 2. The Pre-Lab Quiz Part Two of your preparation process is a Pre-Lab Quiz. This will be given in the lab, at the very start of the period, immediately after your instructor has taken attendance, collected the Pre-Lab Questions, and answered any quick questions from students. You ll want to make a habit of arriving ON TIME and C. Graham Brittain Page 3 of 12 8/31/2008

4 prepared to hand in your Pre-Lab Questions, and then take the quiz. If you re late to lab, you ll forfeit your opportunity to take that week s quiz (and thus you ll have a grade of zero for that quiz). But provided you have your Pre-Lab Questions ready to hand in, you will still be permitted to work the experiment. The Pre-Lab Quiz may include any (or all) of the following concepts from the experiment you ll be conducting: The overall goal or objective of the experiment. The key procedural steps needed to accomplish that goal. The central concept being demonstrated in the experiment. The important safety considerations for the experiment. The method to be used to calculate the experimental results. The physical and/or chemical properties of the substances you ll be working with that day. Any relevant concepts or lab techniques described in this Remedies document, illustrated in an online Pre-Lab Study Assignment, or learned in a previous experiment. Clearly you ll want to initiate your pre-lab study several days ahead of time, so that if you struggle with any of the questions or concepts, you can seek the advice of a lab instructor in the Chemistry TA Help Office. Understand that YOU MUST TAKE RESPONSIBILITY for your own laboratory preparation. Quite literally, if you fail to prepare you ll be preparing to fail because we cannot possibly permit unprepared students to work in a chemistry lab. Use of the Report Sheet You ll see that each one of the experimental write-ups posted on the course website contains a Report Sheet. These are to be completed and ready to turn in promptly at the start of the next meeting of your laboratory class, and they will serve as your Lab Reports. Each of the Report Sheets will typically contain two parts: 1. The learn-as-you-go Lab Notebook for recording your Data and Observations This portion of the Report Sheet is where you ll record your work while you re making your measurements and observations during the experiment. Although you ll want to try to keep it as neat and legible as possible, in this part of the Report Sheet, you can feel free to make mistakes (and then correct them). For example, you might discover an error after you ve already recorded a measurement or an observation, and need to correct your written notes after you ve repeated that experimental step a second (or possibly a third) time. 2. The more formal write-up and presentation of your Results and Conclusions In contrast, this portion of the Report Sheet should be completed only after your experimentation is done, and after you ve worked out how to properly perform the calculations and interpret your results. This part of the Report Sheet will serve as the final, neat and clean, and very formal presentation of your work. Thus if your work here is a bit messy or you realize you ve made some mistakes, you ll want to print a fresh copy of the Report Sheet from the course website and re-write this part of your formal Lab Report. Skills in Recording Data and Observations (DURING your Lab) Recording experimental data and observations is important skill that requires both thought and practice. Students sometimes forget to write down a measurement or an observation, and they often feel that they can simply remember what they observed and record it later. But you ll quickly realize that so much is happening C. Graham Brittain Page 4 of 12 8/31/2008

5 during the course of the experiment, that you can t possibly remember everything! You must concentrate on legibly recording all measurements and observations, at the time that they are made. Some general guidelines for the Lab Notebook portion of your Report Sheet: Write your entries with a blue or black ink pen. You should NOT use a pencil or erasable ink. While you re in lab, keep this portion of the Report Sheet next to you at all times, so you can record your data and observations immediately in the proper place. Never record your work on a scrap of paper. Do your best to write neatly, concisely and LEGIBLY. If you make a mistake, do NOT erase it, cover it with white-out strips (or liquid paper), or scratch through it to the point that your entry is completely obscured. Instead, draw a single line through the error, and write the correct entry nearby. In recording OBSERVATIONS, it s important to keep in mind that you can NEVER write down too much! Most of the questions that come up later (when you re trying to complete your Report Sheet) are the result of insufficient observation or improperly recorded data. (And remember If you did a thorough job of preparing for the experiment, you ll know exactly what to look for and what to record.) When recording OBSERVATIONS of a SUBSTANCE, describe everything that you see (or perhaps smell): Is the substance a solid, liquid, or gas? Is it a solution? What color is it? Is it opaque, translucent, or transparent? If you re instructed to waft the vapors toward your nose, does the substance have an odor? When recording OBSERVATIONS of a REACTION, first write down what you did (heat a solution, or add one chemical to another and mix thoroughly). Then write down what you saw, heard, smelled, or felt with your fingertips: Was there a color change? Did a gas evolve? Did a solid form? Was an odor emitted? Was there any sound? Was any heat evolved? How long did it take before the reaction occurred? Be careful that you have indeed recorded an observation and NOT an inference. Write down ONLY what you actually OBSERVED, NOT what you THINK you observed. For example, a solid substance can be described as a silver-colored metal, but it shouldn t be described as silver metal (which would mean that the solid is a sample of Silver, one of the metals on the Periodic Table of the Elements). Only after you ve thoroughly processed your data and carefully interpreted your observations can you present your results and draw your conclusions. When recording DATA, you must always remember that ALL numerical data MUST be recorded with the UNITS of measurement, and to the appropriate number of SIGNIFICANT FIGURES! (The very first lab is designed to help teach you that the number of significant figures indicates the uncertainty in the measurement. Every measurement will always contain some uncertainty due to the limitations of the measuring device and/or the skills of the observer.) Finally, be sure to have your lab instructor look over and initial/date your observations and data entries before you leave the lab. C. Graham Brittain Page 5 of 12 8/31/2008

6 . Skills in Calculating your Results (DURING and/or AFTER your Lab) 1. Write down the mathematical formula that you re going to use (Example: PV = nrt). 2. Substitute in the numerical values WITH their UNITS. (Numerical values have NO meaning without their units.) 3. Carefully and systematically CHECK THE UNITS all the way through the formula to ensure that the calculation has been set up correctly. Don t EVER assume that the units of the final answer will be what you intended. Check them to make sure! If the intermediate units don t cancel properly to yield the desired units in the final result, then you ve made an error in setting up the calculation. Go back and look for it! You ll be able to catch and prevent frustrating and costly mistakes in processing your data if you just take a moment to check your units. Even after you ve entered all of the numerical values into your calculator and computed the result, you still have TWO more steps to perform: 4. Carefully consider the numerical value of your result. Does it make sense to you? Does the value feel right? Were you expecting a larger number than the one that s shown on your calculator? Or a smaller number? If the number seems odd to you, check your work again! (Check the algebra you used to rearrange the equation so as to solve for the unknown variable. Double-check the units of every value). Then try entering all of the numbers into your calculator a second (or even third) time to verify that you haven t made an error in pressing the buttons of the functions or numbers. 5. Finally, round the value of your result according to the rules of significant figures. Remember that this value is only as good as the numbers you used to calculate it. And remember to report the value with its units. Your PRIMARY goal in working calculations is NOT to get the right number on your calculator. It s to clearly demonstrate the thought process you used to arrive at that result. There are only TWO simple rules to remember when working with significant figures in calculations: 1. When multiplying or dividing: Your final result cannot be any more precise than the least precise value used in the calculation. The least precise value is the one with the fewest significant figures. Seven Sig Figs Three Sig Figs Two Sig Figs X Reported Answer Two Significant Figures 2. When adding or subtracting: Your final result cannot have any greater significance than the least significant value used to produce the result. Another way to say this is that the digit that contains the uncertainty in the result is dictated by the least significant value used in the calculation the one with the uncertainty in the highest decimal place Reported Answer: 23.0 (uncertainty in the tenths place) Reported Answer: (uncertainty in the tenths place) C. Graham Brittain Page 6 of 12 8/31/2008

7 Realize that your calculator does NOT know how to apply the significant rules after it has completed the calculation. This means that YOU MUST be smarter than your calculator! For example, if you multiply two values that contain 3 and 4 significant figures, respectively, the result of your calculation is limited to just three significant figures. The display in your calculator may be able to show as many as seven or eight digits, but YOU must round to only three significant figures, and report the rounded value as your result. In doing this, you re indicating that the uncertainty in your result is in the third digit. On occasion, you may multiply two values together (containing, as in the example above, 3 and 4 significant figures) to find that your calculator displays a result that has fewer digits in it than either of the numbers that you entered (perhaps it displays only two digits). Again, YOU MUST be smarter than your calculator! In this situation, you should realize that the two numbers just happened to multiply to yield a very simple value, and that you re entitled to add one trailing zero so that the final result that you report has three significant figures (with the uncertainty in the third digit). Skills in Making Laboratory Measurements Mass Measurements Your lab is equipped with electronic balances that measure mass in grams up to a certain maximum. If you exceed the maximum capacity of the balance, you may see an error reading on the digital display (or perhaps no reading at all). If that happens, you ll need to find a way to weigh your substance in smaller mass quantities. The balances in most of our undergraduate labs provide mass readings to 1/100 th of gram (0.01 gram). Thus when you record a mass measurement, it should always have two digits past the decimal point. And you should notice that there will be just a bit of fluctuation in the last digit of the display. This digit is the one that contains some uncertainty, and is the last significant figure. Due to this uncertainty, you should never try to weigh a mass that is less than 0.10 grams; there is simply too much fluctuation (too much uncertainty) in the last digit for the measurement to have any meaning. Measuring a mass with electronic balances is relatively easy. If you re measuring a metal sample or a piece of laboratory glassware, you can simply place your item on the balance pan and record the mass. Chemical samples must NEVER be placed directly on the balance pan; their mass should be measured on a piece of weighing paper, or in a beaker or plastic weigh boat. The mass of the paper or empty container can be subtracted out electronically by a process known as taring. The weighing container is placed on the balance, and when a steady reading is reached, the TARE button is pressed. The digital display should then show a zero value. The chemical sample can then be placed in the container, and the mass displayed will be only that of the added sample. When this mass measurement is complete, the balance must be re-tared with the balance pan empty so that it is ready for use by the next student. This is also known as zeroing the balance. Here are some additional considerations when using an electronic balance: These instruments are so sensitive that air flow and other movements around the balance will cause the digital display to fluctuate significantly. Movement should be minimized near the balance in order to get a steady reading. Mass measurements should always be made at room temperature. Containers which are very hot or cold create air currents, which will affect the mass measurement. In particular, the heated air around hot containers has a buoyant effect; the mass of a hot container will appear to increase as it cools on the balance pan. The balances are used frequently and by a great number of students. They are expensive electronic devices, and should be treated with care. Any spills must be cleaned up immediately with a paper towel! C. Graham Brittain Page 7 of 12 8/31/2008

8 Volume Measurements: Use of Graduated Cylinders and Burets Laboratory glassware is calibrated in terms of the volume it contains or delivers; thus each piece is labeled either TC (to contain) or TD (to deliver). These calibrations differ by a small, but significant amount. For example, if a pipet is marked TD, that means that when the pipet is filled to the calibration mark and allowed to drain, it will deliver the volume indicated by the mark. The pipet will still have a small portion of fluid remaining in its tip after it has delivered the proper volume, but this has been accounted for in the calibration. Because the volume of liquids varies with temperature, most glassware is calibrated for use with liquids at 20.0 o C, an average room temperature. It s essential that glassware be kept clean. Immediately after use, glassware should be emptied (into the proper waste container), rinsed several times with tap water, cleaned with a dilute detergent solution and brush, rinsed with tap water again, and finally rinsed with distilled water. After rinsing, a film of water should adhere uniformly to the inside surface of the glass. If the wetting appears spotty, additional cleaning is needed. It s best to let the glass dry by standing at room temperature Graduated Cylinders Graduated cylinders can vary in capacity from 5 ml up to 2000 ml. Most are calibrated to deliver and have a pouring spout at the top. The volume scale increases from the bottom of the cylinder to the top. The surface of a liquid in a cylinder will have a definite curvature called a meniscus. For most liquids, this is a concave curvature, and the volume of the liquid should be read by noting the calibration mark at the bottom of the meniscus. A few liquids (Mercury, for example) have a convex surface; the top of the meniscus is used for measuring the volumes of these substances. The eye must be at the same level as the surface of the liquid in order to observe the correct volume. If your eye is above the meniscus, your volume reading will be too large. If your eye is below the meniscus, your volume reading will be too small. This apparent variation in the volume as observed from different locations is called parallax error. The first lab in the CHM 105 course is designed to help you learn to read the calibration marks on graduated cylinders (and other glassware), and determine the number of significant figures you should record when making your volume readings. C. Graham Brittain Page 8 of 12 8/31/2008

9 Burets A buret is a long, narrow, calibrated tube with a valve (called a stopcock ) at the bottom to control the flow of liquid. Common buret sizes are 10, 25, 50, and 100 ml. Burets are used to make very precise measurements of volume of a liquid that is delivered into another container. If this volume measurement is to also be accurate, the buret must be kept extremely clean. The inner walls can be scrubbed with a buret brush that has been dipped in a dilute detergent solution. The buret should then be thoroughly rinsed, first with tap water, and then will distilled water. Finally, when the buret is ready for use, it should be rinsed several times with small portions of the solution to be delivered, and then filled to above the zero calibration mark at the top of the buret. A funnel can be used for this, but the solution should be poured very slowly, to avoid creating air bubbles or over-filling the buret. The stopcock is then opened to carefully lower the meniscus to the zero calibration mark (or below); any air bubbles in the tip of the buret should be flushed out by this action. Any drop of liquid hanging from the tip of the buret should be dislodged, and the initial volume of the liquid in the buret should be read and recorded. Burets must be handled carefully to avoid loosening and dislodging the stopcock. The recommended method for delivering liquid from the buret is as follows: If you re right-handed, position the buret so the handle to the stopcock valve is to the right (as shown in the figure above) Operate the stopcock with your left hand your finger reaching behind the buret, and your thumb in front of the buret. The right hand is then used to hold (and swirl, if adding one reactant to another) the receiver flask. After the desired volume has been delivered, you should touch the receiver flask to the buret tip to dislodge the final drop. Then, after a pause (to allow the film of liquid on the buret walls to drain to the meniscus), the final volume should be read and recorded. The liquid level should always be read with great care. Note that unlike a graduate cylinder, the volume scale on a buret increases from the top of the buret down to the bottom (indicating the volume of liquid delivered). The smallest increment marked on a 50-mL buret is 0.1 ml, and fifths of each increment can be estimated reproducibly. Thus each volume should be recorded to 0.01 ml. C. Graham Brittain Page 9 of 12 8/31/2008

10 The volume of liquid delivered is the difference between the final and initial volume readings. After use, the liquid in the buret should be drained into the appropriate waste container, and the buret cleaned thoroughly. Separation of Solids from Liquids: Vacuum Filtration Vacuum filtration is an extremely efficient means of isolating a solid substance from a liquid mixture. The vacuum is produced by a water aspirator at the lab bench (the faucet with a short side arm). The rapid flow of water through the faucet draws air through the side arm, generating a partial vacuum. This side arm on the water aspirator is connected to the corresponding side arm of a filter flask using a piece of thick-walled vacuum tubing. Operation of a Burner A special Buchner funnel is secured to the filter flask with a rubber adaptor, and a piece of filter paper (slightly smaller than the perforated plate in the funnel) is placed inside the funnel and pre-moistened with solvent. It s important that the wet paper forms a tight seal against the funnel when the vacuum is turned on; otherwise, the paper may float when the solid/solution slurry is poured into the funnel. The mixture should always be poured slowly into the center of the funnel so as not to overflow it. When filtration is complete, the filter cake is usually washed several times with small amounts of fresh solvent. After several washes, the vacuum can be used to pull air through the filter cake to dry the solid. The filter flask must always be secured by clamping it to a ring stand. The Buchner funnel makes the apparatus top heavy, and the thick-walled vacuum tubing connecting the flask to the aspirator tends to flop around when the water is turned on and off. If not clamped, the filter flask may fall over, spilling the contents of the funnel and possibly the solvent in the flask. The burner is most easily lit if the gas flow rate is intermediate, and the amount of air in the gas-air mixture is low. If the burner has a threaded base, the air intake can be reduced by tightening the rotatable barrel all the way to close off the air ports, and then loosening the barrel just one or two turns. If the burner has a rotatable sleeve over the air ports at the base, the sleeve should be rotated so that the ports are nearly covered. The rubber hose on the burner is connected to the bench-top gas supply valve. The gas flow valve at the base of the burner should be turned to the fully-closed position, and the main gas valve then turned to the fully-open position. The gas flow can then be controlled from the valve at the base of the burner. When lighting a burner with a match, you should light the match first, then open the burner valve just one or two turns. Do NOT hold the lighted match over the top of the burner, but rather bring it up from near the bottom of the burner along the side of the tube until it nears the mouth, and the flame ignites. C. Graham Brittain Page 10 of 12 8/31/2008

11 To light a burner with a striker, you should hold the striker near the side of the mouth of the burner (rather than over the top), and squeeze and release the handle until a spark from the flint ignites the burner. If the burner does not light easily, you should immediately shut off the gas and seek help from your lab instructor. The height of the flame can be adjusted by changing the gas flow rate using the valve at the base of the burner. The temperature of the flame can be adjusted by altering the amount of air in the gas air mixture. Too little air will produce a luminous (yellow) low temperature flame. Increased air flow produces a high temperature, non-luminous flame with an inner blue cone. The hottest part of this flame is at the tip of the blue cone. A noisy flame indicates that the air flow is too high. Before using a burner, you should always make certain that no flammable solvents are being used nearby. If you have long hair, tie it back. If you re wearing long, loose sleeves, you should roll them back to your elbows, and if necessary, secure them with rubber bands. Laboratory Safety Skills Laboratory safety is indeed a skill. In fact, it is the most important skill that you must learn in the laboratory. This basic truth is worth repeating: No experiment or letter grade will ever be more important than your safety and the safety of the other participants in the laboratory. Practicing good safety skills means far more than learning and adhering to the list of safety regulations that are presented in the experimental write-up and the pre-lab discussion. This list usually addresses how to protect yourself personally from accidental exposure to a chemical (via the eyes, skin, or respiratory tract), as well as the actions you should take if you are accidentally exposed. But it s essential to remember that safety is social as well as personal. The laboratory will be filled with other students working on their experiments. You need to be conscious not only of your own actions, but also the actions of the students around you. You must be able to concentrate on your own experiment while still maintaining an awareness of the sights, sounds, and smells elsewhere in the laboratory. Don t ever hesitate to alert other students to potential safety hazards, or to remind them to dispose of waste properly or keep their goggles securely in place. Always, BEFORE you act, give thought not only to your safety, but also the safety of others: If you ve broken a beaker or test tube, alert your lab instructor and your neighbors to the broken glass. Work with your lab instructor to quickly sweep up the glass and deposit it in the broken glass container (not the wastebasket). If your neighbors break some glassware, help them to alert others, and then offer your assistance in the clean-up. If you ve spilled a chemical, alert your lab instructor and your neighbors to the potential hazard. Carefully follow the lab instructor s directions to clean up the chemical, and be sure to do it thoroughly so that the next student using your work area is not exposed to any residue. If your neighbors spill a chemical, help them to alert others, and then offer your assistance in the clean-up. Whenever you re using a burner or a hot plate, be sure that you know the fire hazards of all chemicals in your neighbors work area as well as in your own. Never walk away from a chemical that is being heated and leave it unattended. If you and your lab partner are working on different parts of an experiment, the two C. Graham Brittain Page 11 of 12 8/31/2008

12 of you must have a clear understanding as to who is responsible for keeping a watchful eye on the hot plate or burner. You must become SO certain of the locations of the safety features of the laboratory (exits, fire extinguisher, safety shower, eye-wash fountain, fire blanket, and emergency telephone) that you can find any one of them instinctively even in a room filled with smoke and the lights out. Memorize the telephone number that you would call in an emergency. Pay particular attention to the evacuation route planned for your laboratory. If your room or the building needs to be cleared, you must rendezvous with your instructor and classmates at the designated meeting place so that the fire personnel can account for everyone s safety. Always remember that working in a laboratory is like sitting in the exit row of an airplane: You must understand what to do and be willing to help in the event of an emergency. You should be ready not only to follow your lab instructor s directions, but also to assist your instructor in responding to the emergency, perhaps by telephoning for help or guiding your neighbor in the use of the eye wash fountain or safety shower. Let me reassure you that this discussion is not at all intended to make you fearful about working in the laboratory or coming into contact with chemicals. But it s very much intended to help you realize how important it is that you be familiar with the safety hazards of each experiment and the safety practices of the lab. Just like traveling on an airplane, working in a chemistry lab is safe and enjoyable, as long as you ve thoroughly prepared to conduct the experiment and consistently practice good safety behavior. C. Graham Brittain Page 12 of 12 8/31/2008