CHEM 2301 Final: CHEM 2300 Final Exam Winter 2002.PDF
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Evaluating Proposals Presented below are four preliminary student proposals (numbered 1 through 4) to quantitatively characterize and finely control the light emitted from glow stick chemistry with the objective of identifying one or more trends.
Proposal 1
Activate a green glow stick. Open and transfer activated solution into a 1 dram (3.7 mL) vial. Add 5 mL of 0.1 M sodium salicylate in ethanol at room temperature (20 oC) by transfer pipette. Mix well. Now measure the intensity by emission spectrometer. Next, change the temperature to 40 oC. Measure the intensity. Continue in 20 oC increments until 100 oC. Plot intensity vs. temperature (in oC). Look for trends.
Proposal 2
Activate a green glow stick. Label two 1 dram (3.7 mL) vials âAâ and âB.â Open glow stick and transfer 3.00 mL of activated solution into vial âAâ and another 3.00 mL into vial âBâ over a spill containment bin. Cap both and record the emission spectrum via emission spectrometer of both to confirm equivalent output, establish a baseline and determine λmax. To vial âAâ introduce every 30 seconds 20 µL of 0.1 M KOH by 20-200 µL micropipette set at 20 µL. Immediately recap and mix by four gentle inversions, then record the emission spectrum. Repeat cycle for a total of 10 minutes. At 10 minutes record the emission spectrum for vial âB.â Pipette 20 µL of 0.1 M KOH into vial âBâ, mix and immediately record the emission spectrum. Use the results from vial âBâ to confirm that the activated solution light output remains reasonably constant over 10 minutes (or if it deviates, by how much) and when challenged at 10 minutes with 20 µL of 0.1 M KOH the system at 10 minutes responds as it did at 30 seconds with vial âAâ (and if it doesnât, by how much). Plot the intensity at the λmax versus volume of 0.1 M KOH. Analyze for trends.
Proposal 3
Use three red glow sticks. Combine activated red glow stick solution into vial. Distribute 3 mL of this activated red solution into six separate 2 dram (7.4 mL) vials. Treat vials according to the following schedule:
| Vial | Acid (0.01 M HCl in ethanol) | Temperature (by ice bath or hot water bath) |
| 1 | 1 drop | 60 oC |
| 2 | 5 drops | 0 oC |
| 3 | 10 drops | 60 oC |
| 4 | 15 drops | 0 oC |
| 5 | 20 drops | 60 oC |
| 6 | 25 drops | 0 oC |
Drops are by estimated by transfer pipette. Look for light intensity by eye; record if the activated solution is intense or dead. Look for interesting trends.
Proposal 4
Activate two red glow sticks. Combine activated solution (â16 - 18 mL) in a 20 mL plastic vial. Distribute 3.00 mL of this activated solution into five separate, labeled 1 dram (3.7 mL) vials. To each vial, add a different volume (50, 100, 150, 200 and 250 µL) of 0.1 M sodium salicylate in ethanol; do this at roughly the same time, in other words as simultaneously as possible. Mix well for 3 seconds and record the intensity vs. λ using an emission spectrometer. Determine λmax and the plot the intensity at the λmax versus volume of 0.1 M sodium salicylate. Analyze for trends.
Question 1 (2 p) List ALL the proposals that are quantitative.
Question 2 (2 p) List ALL the proposals that vary only ONE variable at a time (and have a reasonable chance of holding all other variables constant).
Question 3 (2 p) List ALL the proposals that clearly include a positive control. Positive controls demonstrate the system is functioning to give a result when there should be a result. For example to confirm the system gives the same response over time.
Question 4 (2 p) List ALL the proposals that clearly include negative controls. Negative controls confirm the system gives no results when results should be absent.
Question 5 (2 p) List ALL the proposals that change the independent variable in fine increments to permit the discovery of trends that have predictive power.
