The spectra of different flavors will be provided by your instructor You need

The spectra of different flavors will be provided by

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(a) Set the colorimeter to the desired wavelength. The spectra of different flavors will be provided by your instructor. You need to determine which wavelength is appropriate for your trial (see introduction). using the <> keys above CAL. (b) Three-quarters-fill a cuvet with deionized water (DI), wipe the outside of the cuvet with a lint-free cloth, and inspect to ensure that there aren’t air bubbles or streaks. Gently tapping the bottom of the cuvet on the bench top may dislodge an air bubble. (c) Open the thumb latch below, “Vernier,” place the cuvet in the colorimeter with a clear side aligned with the white arrow within, and snap the door closed. (d) Press the calibrate button once, firmly, wait for the red light to stop blinking, and confirm that the absorbance reading is 0.000. (e) Place the other cuvet, ¾-filled with DI water as in 2.(b) above, into the calorimeter. Its reading should also be 0.000. (f) Because less absorbance than the “blank” isn’t displayed as a negative value on the colorimeter, again press calibrate, wait for the red light to stop blinking, and confirm that the reading is, yet again, 0.000. (g) Replace the second cuvet in the colorimeter with the original one. Do not press calibrate this time! The reading should again be 0.000. If so, you have a matched set of cuvets. If not, recheck both cuvets for air bubbles, fingerprints, and streaks, fix the problem, or choose two other cuvets, and repeat steps 2.(a)-(g).
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3. (a) While one student is performing step 2. the other should prepare the first assigned Kool-Aid® stock solution using the mix packet obtained from your instructor. You will need a 1-L volumetric flask, if available, or a 2-L or 3-L beaker (beakers are lower-precision instruments, typically ±5% of stated volumes). Record the flavor, its labeled mass, and weigh the unopened packet. (b) Keeping all the packaging and keeping that dry,transfer the contents of the packet to the flask or beaker (a powder funnel and a wash bottle filled with DI water may be helpful). Weigh the emptied package, including any paper you may have torn off to open it. Calculate the mass of mix transferred by difference. (c) Dissolve the mix in about ¾ of the target volume of DI water in your vessel, and then bring the volume up to the mark with more DI water. Mix thoroughly (this is now your stock solution). Part B: Beer’s Law Plots, Concentration of Unknowns 4. Rinse one of your cuvets from step 2.(g) three times with your stock solution, dumping the rinses into a ~100 mL waste beaker. Fill the cuvet ¾ full, wipe the sides with a lint-free wipe, check for air bubbles, and read its absorbance vs. your blank cuvet at the wavelength you’ve chosen. 5. Make five precision dilutions of your stock solution aiming for absorbances spread roughly between 0.050 and 1.000. First, use a 10 (or 5) mL volumetric pipet (rinse it with a few mL of stock solution), transfer that amount of stock solution to a 100 mL volumetric flask, dilute to the mark with DI water, mix thoroughly, rinse the cuvet three times, ¾ fill the cuvet, and read its absorbance. 6. Based on the absorbance reading of the diluted solution in Step 5, and the target absorbance range 0.05-1, choose
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  • Spring '06
  • THOMAS

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