EXERCISE 1 Lab Procedures I Familiarize yourself with the equipment on display in the lab Several items that you will be using during the semester are on display in the lab Pasteur pipet and bulb blow out pipet delivery pipet transfer pipet pipet filler micropipettor graduated cylinder test tube Erlenmeyer flask top loading balance centrifuge tube Eppendorf tube Eppendorf tube holder magnetic stir bar beaker Spec 20 cuvette disposable cuvette Petri dish squeeze bottle liquid dispenser Parafilm weigh boats Examine each item and make sure you are able to recognize and name it Make a simple sketch of any unfamiliar items in your laboratory notebook for study purposes II Compare the accuracy and precision of volumetric measuring devices In this part of the lab you will use a 100 mL beaker a 100 mL graduated cylinder a 10 mL graduated cylinder a 5 mL pipet and two different micropipettors 20 200 L and 100 1000 L to measure specified volumes of deionized water After measuring each volume you will weigh the water and record the results Later you will carry out some statistical tests to compare the accuracy and precision of your measurements IMPORTANT Before you begin copy the following table into your lab notebook so that you can use it to record your results Data collected during lab should always be recorded directly into your lab notebook NOT into your lab manual or on loose sheets of paper Recording data into your lab manual or on loose sheets of paper and then copying it into your notebook increases the chance that the data will be lost or that errors will be made during the transfer Weight of Water Measured by Various Volumetric Measuring Devices Trial 100 mL beaker g 100 mL graduated cylinder g 10 mL graduated cylinder g 5 mL pipet g 20 200 L pipettor g 100 1000 L pipettor g 1 2 3 4 5 6 7 8 Exercise 1 Austin Community College BIO 1406 Laboratory Manual 12th Ed Copyright 2006 1 15 IMPORTANT Before you make any measurements make sure you calibrate your electronic balance In addition as you carry out your experiments make sure every member of your group has a chance to practice using each measuring device A How accurately and precisely do beakers measure volume 1 Measure 60 mL of dH2O using a 100 mL beaker When making your measurement be sure the lowest point of the meniscus just touches the 60 mL calibration mark on the beaker You can use a Pasteur pipette with a small bulb to add or remove water adjusting the volume as close to 60 mL as possible 2 Place a large at least 10 cm x 10 cm plastic weigh boat on your electronic balance and tare the balance to zero Carefully pour all of the dH2O from the beaker into the weigh boat and record the weight to the nearest 0 01 g in your data table Finally discard the dH2O into the waste receptacle provided place the weigh boat back on the balance and re tare the balance 3 Repeat this procedure seven more times using the same beaker for a total of eight measurements B How accurately and precisely do graduated cylinders measure volume 1 Measure out 60 mL of dH2O using a 100 mL graduated cylinder When making your measurement make sure the lowest point of the meniscus just touches the 60 mL calibration mark on the graduated cylinder You can use a Pasteur pipette with a small bulb to add or remove water adjusting the volume as close to 60 mL as possible 2 Determine the weight of the dH2O measured with the 100 mL graduated cylinder Follow the same procedure you used to weigh the dH2O from the beaker Record the weight to the nearest 0 01 g in your data table Finally discard the dH2O into the waste receptacle provided place the weigh boat back on the balance and re tare the balance 3 Using the same graduated cylinder measure and record the weights of seven more 60 mL volumes of dH2O for a total of eight measurements 4 Now repeat the procedure eight more times using a 10 mL graduated cylinder to measure 3 mL volumes of dH2O Record the results in your data table C How accurately and precisely do pipets measure volume 1 Pipet fillers are designed to draw liquid into a pipet and accurately deliver specific volumes Before you make any measurements learn how to use the pipet filler by carefully reading the instruction sheet provided Ask your instructor for help if you do not understand the instructions 2 Insert the top blunt end of a 5 mL blow out pipet into the pipet filler The pipette should be attached firmly but do not push it in too far or it will be difficult to remove when you are done 3 Immerse the tip of the pipet into a container of dH2O and practice using the pipette filler to slowly fill and empty the pipet If you are having difficulty ask your instructor for help IMPORTANT Never allow liquid to be drawn into a pipet filler since that could damage the filler and certainly would contaminate the liquid being delivered 4 Use the pipet filler to slowly fill the pipet with slightly more than 3 mL of dH2O Note that pipets are usually calibrated in reverse so that the zero mark is near the top and the calibration marks increase towards the tip In this case the calibration marks show how much liquid has been delivered assuming the pipet was originally filled to the zero line not the amount the pipet contains Therefore if a 5 mL pipet is filled slightly above the 2 mL line it will contain slightly more than 3 mL Exercise 1 Austin Community College BIO 1406 Laboratory Manual 12th Ed Copyright 2006 1 16 5 Raise the tip of the pipet out of the water and use the pipet filler to slowly release dH2O back into the container until the bottom of the meniscus exactly reaches the 2 mL line on the pipet i e the pipet contains exactly 3 mL of dH2O Touch the tip of the pipet to the inside of the container to remove any water on the outside of the tip You will next transfer this measured volume to a weigh boat Be sure the pipet remains vertical and no water escapes during this transfer 6 Place a weigh boat on an electronic balance tare the balance to zero and release all 3 mL of dH2O from the pipet into the weigh boat IMPORTANT After the water drains out of the pipet follow the instructions on the instruction sheet to expel the small amount of water remaining in the tip If necessary ask your instructor for help After all water has been expelled from the pipet touch the tip of the pipet to the weigh boat to remove any water suspended from the tip Record the weight in your data chart and then re tare the balance 7 Using the same pipet measure and record the weights of