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1、Serial Dilution however, it is not food coloring, but a laundry dye so it WILL stain you and your clothes. Please be careful when transferring and transporting solutions.To each of the 9 empty cuvettes students should add 3.00 mL of water from a beaker using a pipet and bulb.We will be diluting the
2、original acid solution by a factor of 2 into each of the remaining 9 cuvettes. The group should begin by transferring 3.00 mL of the contents of cuvette 1 into cuvette 2 using the pipet and bulb. Once the solution in cuvette 2 has been mixed thoroughly, as shown by the teacher, the group should tran
3、sfer 5.00 mL of the solution in cuvette 2 to cuvette 3 using the same technique. This procedure is repeated until all of the dilutions are complete.Each group will then obtain an unknown solution of simulated nitric acid. The letter of the unknown should be recorded and the group should decide which
4、 cuvette (1-10) the unknown matches most closely and record its number. Part 2: Spectronic-20 Analysis Each group will use the Spectronic-20 instrument to measure the absorbance of the solutions from part one. The Spectronic-20 should be set at a wavelength of _ nm for these measurements. First, stu
5、dents should measure a blank solution (just water) and set the absorbance measurement at zero to calibrate the instrument.Each cuvette should be measured and their absorbance values should be recorded. Later these values will be used to prepare a calibration plot of absorbance vs. dilution number. T
6、he absorbance should be measured and recorded for the unknown solution used in Part 1. Make sure you have recorded the unknown letter.The dilution number and concentration of the unknown will be determined based on the previously constructed calibration curve.Post-Lab Questions:Name: _ Date: _ Hour:
7、 _ 1. What is the name of the point at which you measure the volume of a solution in a pipet or graduated cylinder? _2. If the initial concentration of your acid in cuvette 1 was 15 M, what was the concentration of the solution in the 2nd cuvette? What was the concentration in the 5th cuvette?3. Why
8、 do you need to calibrate the Spectronic-20 with a blank first?4. If I forgot to wipe the cuvette with a Kim Wipe and there were fingerprints of the glass, how could this affect the value of the absorbance read by the spectrophotometer? Would it increase or decrease the absorbance value? Explain.5.
9、On the graph paper provided, plot the absorbance vs. the cuvette/dilution number for each of the solutions measured. Start with the most dilute solution near the y- axis as shown in class. From this plot, determine the cuvette/dilution number of the unknown solution and label the point on your graph
10、. Unknown Letter: _Matching Cuvette/Dilution # from graph: _ Explain how you found this.6. Calculate the concentration of the unknown cuvette assuming that the original acid solution had a concentration of 15 M. (Show your work for full credit)_7. What volume of the original acid solution (15 M) would you need to use to make a 20.00 mL solution with a concentration of 4 M? (Show your work for full credit)_8. Explain the procedure you would use to prepare the solution in question 7 using the techniques learned in lab.Name: _
