General Lab Skills and Equipement Post Lab Awab Magzoub-1

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University of Minnesota-Twin Cities *

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3301

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Chemistry

Date

Jan 9, 2024

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docx

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Uploaded by ProfessorSandpiperMaster1000

Pipetting 1. What should you be careful not to do when turning the plunger/knob to set the volume on a micropipette? When adjusting the knob one should be careful that the value isn’t above the max or below the minimum volume for that particular micropipette. 2. List the volumes that are displayed in the three pipettor volume windows below. Remember to include units. P20 volume: 16.5 ul P200 volume: 11 ul P1000 volume: 1000 ul P20 P200 P1000 1 1 1 6 1 0 5 0 0 3. Which stop (point of resistance) should you press the pipettor's plunger to when you are preparing to draw up liquid? The first stop point should be pressed when drawing up liquid. 4. What was the final volume you should have had in your microfuge tube at the end of the pipetting activity? Did you achieve this volume on your first try? If you did, list two tips you would give a fellow student who was learning to use a micropipettor. If you did not, did you have too much or too little water in your tube? List at least two reasons you may have had the wrong volume the first time. Serial Dilutions 5. Do the following unit conversions: 1 nL = 1000 ____ uL

20 uL = 0.02 ____ mL 450 mL = 0.45 _ L 6. Imagine that you were working in the lab, and you had an 80% stock solution of a blue dye. You needed 10 ml of a solution that was 0.0001% blue dye for an experiment. What volume of the blue stock solution would you need? What volume of diluent would you need to reach 10 ml of the desired concentration? Remember C 1 V 1 =C 2 V 2 The volume of diluent needed would be 0.0125 ul. 7. In the above question, does the volume you calculated for the stock solution seem like a volume you could pipette easily with a standard lab micropipette? How does this relate to the importance of being able to make serial dilutions? The volume from the previous question would not be easily pipetted using a standard lab micropipette. However, through multiple dilutions it would be possible with a standard lap micropipette. Serial dilutions allow for very small concentrations of the blank cuvette (water vs. something else). The blank provides a point of comparison to test the absorption against. The solvent is used as a baseline so it can negate any interference that could be caused. 9. Why is it important to only touch the ridged or frosted sides of the cuvettes when doing spectrophotometry? substances to be transferred without the need for overly expensive materials. Spectrophotometry 8. Explain the purpose of the blank (sometimes called a baseline) when using a spectrophotometer. Include information about how you know what substance to put in It is important because the oils that are secreted by the skin could interfere with the readings and give an inaccurate absorption values 10. Copy and paste your data table showing the absorbance values of your blue food coloring dilution series (Table 2 from the lab document). Alternately, you can upload the table as a separate file and make a note of that here. Sample Blue food color concentration (%) Volume of sample to add (μl) Volume of water to add (μl) Total volume (μl) A 1.0 Sample A is available in the lab 1500 (1.5 ml) B 0.5 750 μl of sample A 750 1500

C 0.1 300___ μl of sample ___ 1200 1500 D 0.04 600___ μl of sample ___ 900 1500 E 0.01 375__ μl of sample ___ 1125 1500 F 0.004 600___ μl of sample ___ 900 1500 G 0.001 375____ μl of sample ___ 1125 1500 H 0.0004 600____ μl of sample ___ 900 1500 I 0.0001 375___ μl of sample ___ 1125 1500 Sample Blue food color concentration (%) Absorbance A 1.0 Error >3 B 0.5 1.939 C 0.1 0/744 D 0.04 0.429 E 0.01 0.262 F 0.004 0.233 G 0.001 -0.046 H 0.0004 0.009 I 0.0001 0.215

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