Introductory Laboratory Techniques

Introductory Laboratory Techniques INTRODUCTION Introductory Laboratory Techniques INTRODUCTION You will find that experimentation will helpyou understand the lecture material since chemistry is an experimental science. In thelaboratory you will go over many practical applications of the theories you learn in class.Use the laboratory as a study aid to help you understand chemistry and even have fun! Many students do not enjoy laboratory and do not find it helpful because they take a "cookbook" approach to chemistry. That is, they are thinking, "I mix 1 gram of this with 5 mL of that to get a blue solution with white stuff at the bottom". They do nothing more than follow the recipe without thinking about what is happening in the test tube and how it relates to what they are studying and to the rest of the world in general. Since we don't let you eat the end results of what you cook in lab, if you take the cookbook approach you are going to have a poor experience in the laboratory and an especially hard time completing your laboratory reports. This lab manual is written to help you avoid such a bad experience and to help you develop skills in solving problems. You will not find recipes in your experiments; you are given considerable leeway in designing your own experiments. Whenever you need a lab technique you will be given complete instructions on how to execute it, but you must be able to figure out how to apply those techniques in discovering the solutions to the problems presented. It is critical that you read the experiment before coming to the laboratory, and attempt to understand the theory behind the experiment and the methods you will use in the laboratory to investigate that theory. Consider yourself an investigator while you are in the laboratory. For example, in a typical reaction first find out "who done it"; what chemicals take part in the reaction? Then find out the culprits' "method"; is energy taken in or given off? Finally you need to find out the consequences; what compound is formed? If you take this approach you will have a better laboratory experience, and you will have a much easier time writing the experimental report. In short, you will learn more and learn more easily. This lab is designed to 1) acquaint you with the equipment in your locker, and 2) introduce you to some basic laboratory techniques. A word of warning: a few of you may find this and other beginning laboratories in Chemistry 2A to be somewhat tedious, especially if you've had a good high school chemistry laboratory course. However, please be patient as the goal is to give all students a good common background so every student has an excellent chance of success with the later, more difficult experiments. Remember that as prelaboratory preparation, you should come to the laboratory with Title, Purpose, Procedure, and Data Tables entered in your notebook. At the end of the laboratory period you should have your TA sign and date your laboratory notebook near your data tables. At the next laboratory meeting you will submit a completed report. 1 Introductory Laboratory Techniques PROCEDURE Common Laboratory Procedures You will now do a set of simple experiments to teach you the proper techniques for using the different equipment in the laboratory. You must read the common laboratory procedures section of this manual before beginning this part of the exercise. These pages describe the proper use of equipment. In these procedures you will learn to properly: a) use a balance, b) measure the volume of a liquid, and c) use a Bunsen burner. A record of all data should be placed in your laboratory notebook. All calculations should be carefully and clearly shown as well. Finally, be sure to answer all questions before turning in your report to the teaching assistant. Safety: Wear your PPE. Use a bulb with an Eppendorf tip to fill a pipet. PROCEDURE You will work in pairs on this experiment. The actual data analyses and the written reports must be done entirely independently of your lab partner or other students. Make sure that you avoid unauthorized collaboration and plagiarism. All suspected violations of the Code of Academic Conduct will be referred to Student Judicial Affairs. Stock Chemicals Used Chemical Maximum Amount Used Manganese Sulfate, monohydrate (s) 1.0-1.2 g Part I. Measuring Volumes A. Using a Pipet to Measure Volume 1. Draw about 400 mL of deionized water into a clean beaker, and let it stand for 15 minutes to equilibrate to room temperature. Note, there is only one deionized water tap in the lab room; make sure you use the correct tap. Helpful hint: You will need to take turns with your locker-mate using the 10.00 mL volumetric pipet. One of you should start part B, using a buret to measure volume, while the other is doing part A. 2. 2 Confirm that your 10.00 mL volumetric pipet is clean by filling to above the mark with deionized water and then letting it drain. Your pipet is a transfer pipet that is calibrated “to deliver” (TD) rather than “to contain” (TC). The last drop of liquid should not drain out of the tip of a TD pipet in normal use. However, there should Introductory Laboratory Techniques PROCEDURE be no water drops left on the side walls. The presence of such drops indicates that your pipet is dirty. Helpful hint: You will use your pipet in many of the experiments in Chemistry 2. It is important that you always clean it at the end of the day, and rinse it thoroughly with deionized water before storage. Pipet cleaning solution is located in a 1 L bottle at the front of the room. Follow the instructions on the label. Remember that your pipet is calibrated to deliver. 3. Measure and record the mass of a clean 125 mL Erlenmeyer flask. 4. Measure and record the temperature of the room and of the water that was set aside in step 1. The two temperatures should agree before you continue. Read the thermometer to the closest one tenth of a degree, using your best estimate. Please be especially careful with the thermometer. 5. Use your pipet to deliver 10.00 mL of the equilibrated water into the Erlenmeyer flask. Note the precision used here. 6. Measure and record the mass of the flask and the water. 7. Repeat steps 5 and 6 at least two additional times without emptying out your flask between trials. 8. Calculate the mass of water delivered by your pipet for each trial. Use your mass of water and the volume of the volumetric pipet to calculate the density of water for each trial. Calculate the average density, standard deviation, and the 90% confidence limits for the average density. 9. Use the temperature of your water along with the values of mass and volume of water given in Table I to calculate the accepted values for the density of water. 3 Introductory Laboratory Techniques PROCEDURE 10. Determine the relative error with respect to the average density of water. The relative error is defined by: relative error = |experimental result - accepted value| accepted value x 100 Table I. The volume occupied by 1.0000 g water weighed in air against stainless steel weights. Temperature (°C) Volume (mL) 18 1.0024 19 1.0026 20 1.0028 21 1.0030 22 1.0033 23 1.0035 24 1.0037 25 1.0040 26 1.0043 Table I gives the corrected volume in mL occupied by 1.0000 g of water when weighed in air against stainless steel weights for different temperatures. Two effects are included in this volume per 1.0000 g; first, the change in the density of water with temperature; and second, a much smaller correction due to buoyancy. The buoyancy correction arises since the balance was set to zero with a certain mass of air on the balance pan. The volume of water displaces some of this air from the balance pan that makes the water appear lighter than it really is. The contribution of buoyancy to the results in Table I is roughly 0.0011 mL per 1.0000 g of water. B. Using a Buret to Measure Volume 1. Discard the water in your Erlenmeyer flask, and re-measure the mass of the flask. The inside of the flask need not be completely dry because any water left in it is from the previous procedure and is at the same temperature as the new water you will be adding. 2. Use a 25 mL buret and accurately measure out about 12 mL of room temperature deionized water from part A into the flask. You should read the buret to the closest one hundredth mL (e.g., 12.14 mL). In your laboratory notebook, record your initial buret reading and your final buret reading. The volume of water delivered by the buret is the difference between the final and initial buret reading. 3. Measure and record the mass of the flask and the water. 4 Introductory Laboratory Techniques PROCEDURE 4. Repeat steps 2 and 3 at least two additional times without emptying out your flask between trials. 5. Calculate the mass of water delivered by your buret for each trial. Use your mass of water and the volume of the water delivered by your buret to calculate the density of water for each trial. Calculate the average density, standard deviation, and the 90% confidence limits for the average density. 6. Assuming that the water temperature has not changed, compare your experimental value of the density of water to the accepted value of the density of water you calculated in part A. 7. Determine the relative error with respect to the average density of water when measured by the buret. Always clean your buret after use and rinse it with deionized water before storage. Furthermore, be sure you follow the instructions given at the beginning of this manual for proper use of the buret. C. Using a Beaker to Measure Volume 1. Measure and record the mass of clean and dry 100 or 150 mL beaker. Note this beaker needs to have a 50 mL graduation mark. 2. Use your clean and dry 100 or 150 mL beaker and carefully measure out 50 mL of your room temperature water. 3. Measure and record the mass of the beaker and the water. 4. Empty out your beaker and carefully measure out another 50 mL of your room temperature water. There is no need to reweigh the empty beaker. 5. Measure and record the mass of the beaker and water. 6. Repeat steps 4 and 5 at least once more 7. Use your mass of water and the volume of the water measured by your beaker to calculate the density of water for each trial. Calculate the average density, standard deviation, and the 90% confidence limits for the average density. 8. Assuming that the water temperature has not changed, compare your experimental value of the density of water to the accepted value of the density of water you calculated in part A. 9. Determine the relative error with respect to the average density of water when measured by the flask. 5 Introductory Laboratory Techniques PROCEDURE Part II. Drying a Hydrate 1. As illustrated by the TA, place a clean crucible on a wire triangle above a Bunsen burner. With the TA watching, light the Bunsen burner and adjust the flame and the height of the wire triangle so that the crucible is positioned in the hottest part of the flame. 2. Heat the crucible for five minutes to make sure it is dry, and then remove it from the wire triangle using crucible tongs and place it on your desktop to cool. 3. After the crucible has returned to room temperature (approximately five minutes), measure and record its mass to the thousandth of a gram (milligram). 4. Weigh into your crucible 1.0 - 1.2 g of manganese(II) sulfate monohydrate, MnSO4•H2O, recording the exact mass to the thousandth of a gram (milligram). 5. Heat the crucible with its contents for five minutes, and then remove it to your desktop using crucible tongs. 6. After the crucible and its contents have returned to room temperature, measure and record the mass. 7. Repeat steps 5 and 6 until the mass readings are consistent. (Mass no longer decreases after heating.) 8. Calculate the mass loss by your sample upon heating. 9. Transfer the contents of your crucible to the waste container located in the fume hood. Clean-up: Solid dry manganese(II) sulfate may be disposed of in the proper waste container found in the fume hood. Clean your volumetric pipet and buret with deionized water only. All other glassware may be cleaned with tap water and rinsed with deionized water. Always, let your glassware air-dry. If time permits, now would be a good time to also clean any other dirty glassware in your locker. Be sure that all glassware is returned to the proper place, and that your laboratory bench has been rinsed with water using a sponge. Inform your TA that you are leaving and be sure that your laboratory drawer gets locked. 6 Introductory Laboratory Techniques DATA ANALYSIS DATA ANALYSIS Part IA. Measuring Volumes with a Pipet For each of your three acceptable trials, what was the measured mass of water delivered by your 10.00 mL pipet? For each of your three acceptable trials, what was the density of water that you determined with your 10.00 mL pipet? Using the data from your three trials with the 10.00 mL pipet, what is the average, standard deviation, and 90% confidence limits of the average? What was the temperature of the room and the temperature of the water to the closest degree Celsius when you made your measurements for this laboratory? Referring to Table I in the laboratory manual, what is the accepted value for the volume of 1 gram of water at the temperature you reported in question 4? Using the appropriate volume of 1 gram of water from Table I, what is the accepted value for the density of water at the temperature of your measurements? Using your average value for the density of water determined with your 10.00 mL pipet and the accepted value for the density of water, what is the relative error in the density that you determined with your 10.00 mL pipet? Part IB. Measuring Volumes with a Buret For each of your three acceptable trials, what was the volume of water that you measured with your buret? What was the mass you determined for each corresponding volume that you measured with your buret? For each of your three acceptable trials, what is the density of water that you determined with your buret? Using the data from your three trials using the buret, what is the average, standard deviation and 90% confidence limits of the average. Using your average value for the density of water determined with your buret and the accepted value for the density of water that you found in question 6, what is the relative error in the density that you determined with your buret? 7 Introductory Laboratory Techniques DATA ANALYSIS Part IC. Measuring Volumes with a Beaker For each of your three acceptable trials, what was the volume of water that you measured with your beaker? What was the mass of water that you determined for each corresponding volume that you measured with your beaker? For each of your three acceptable trials, what is the density of water that you determined with your beaker? Using the data from your three trials using the beaker, what are the average, standard deviation and 90% confidence limits of the average? Using your average value for the density of water determined with your beaker and the accepted value for the density of water that you found in question 6, what is the relative error in the density that you determined with your beaker? If you wanted to accurately measure a 20.00  0.02 mL volume of a liquid, which piece of glassware would you use; 10.00 mL pipet, buret, or Erlenmeyer Flask? If you wanted to quickly measure about 20 mL, which would you use? Generally, a pipet is more accurate than a buret. Do your experimental results support this statement? If yes, explain. Explain why a student’s experimental results may not support the statement? Part II. Drying a Hydrate What was the mass of your empty crucible? What was the mass of your crucible + MnSO4·H2O? What was the initial mass of your sample of MnSO4·H2O? What was the final mass of your crucible + sample after you had heated it to constant weight? What was the final mass of your sample? What was the mass lost by your sample upon heating? What is the chemical formula of the final product? What is the theoretical percent mass of water in manganese(II) sulfate monohydrate? Calculate your experimentally determined percent mass of water in manganese(II) sulfate monohydrate. What is your relative error with respect to percent mass of water in the monohydrated sample? 8 Introductory Laboratory Techniques DATA ANALYSIS Why did your empty crucible need to be dried by heating? If your crucible had not been dried before heating the sample how would that have affected your calculations in Question 28? 9 Nomenclature Lab INTRODUCTION Nomenclature Lab INTRODUCTION Whenever you begin study of a new field, what do you have to do first? You have to learn the language of that field. Every field of study has its own vocabulary. Thus, before you can communicate you have to learn the words that people use in that field, or you will have a very hard time learning the concepts that are being taught. This is certainly also true in chemistry. In chemistry we use words that you may or may not have heard before such as electrolysis, effusion, hybridization, resonance, and stoichiometry. Chemists also use words that have a different meaning than the common definition such as the word mole. Therefore, a good grasp of the language of chemistry is critical to your success in a chemistry course. However, studying a new language is difficult and not considered enjoyable by many people. Luckily, when instructors teach chemistry they generally try to use the new words only when they need them making the learning of the language much easier. However, there is one part of the chemical vocabulary that simply can't be put off, and that is the language of chemical nomenclature. When instructors talk about the properties of chemicals (which is what chemistry is!), it is critical that you recognize the chemical that is being discussed. For example, if during the discussion of chemical reactions an instructor mentions that potassium chlorate is heated to produce potassium chloride and oxygen, it is critical that you are able to write the chemical reaction for this process. Thus you must learn chemical nomenclature as soon as possible. As further impetus to your study keep in mind that studies show a good correlation between learning nomenclature and final course grade. That is, students who learn nomenclature early and well have greater success in the course. How do you learn chemical nomenclature? You practice and practice and practice. The following pages contain notes that have been prepared as an aid in your pre-workshop preparation. Please read these over carefully before coming to the laboratory. ASSIGNMENT View the On-line Prelab Presentation of Nomenclature. It is a detailed presentation of the rules of nomenclature. Examples are given in the presentation, as well as, practice problems. Complete the 50 point/50 question on-line quiz. You can find it under “Post-Laboratory” in the on-line program. Unlike the prelab quizzes, you can log out of the quiz at any time without penalty and continue the quiz later. The on-line program times out at 20 minutes. Also, unless you click on the submit button for the particular question you are working on, the program will not count the question against you. For example, if you are working on question 10 when the program times out or you log out, the program will begin at question 10 the next time you log-in to continue the Nomenclature quiz.