III. Procedure This assignment uses a PET virtual lab. Using a computer that is running Microsoft windows or Macintosh O

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Iii Procedure This Assignment Uses A Pet Virtual Lab Using A Computer That Is Running Microsoft Windows Or Macintosh O 1 (78.63 KiB) Viewed 15 times

III. Procedure This assignment uses a PET virtual lab. Using a computer that is running Microsoft windows or Macintosh OS 10.1 or higher, go to Beer's Law Lab 1.4.20 (colorado.edu) Part 1: Generate the absorption spectrum and find max for a solution of NiCl₂(aq) 1. Use the PLAY button to open the application. 2. The Beer's Law Lab simulation has two panels. The 1st panel is a concentration game. You can add materials and water to the tank and change the concentration (drag the "cross- haired" meter to the tank to measure concentration). The 2nd panel is what we're after, "Beer's Law." This will open the simulation of the interior of a spectrophotometer. You will see that the pieces inside the spectrometer are laid out on the screen. From left to right, you will find a. The light source - a white light bulb that can be divided into the colors of the rainbow, one color at a time by adjusting the wavelength on the slider below the light source. b. You will see the sample in its cuvette but shown in cross-section. You can drag the ruler up to the cuvette to measure its width. c. A meter that allows you to measure in absorbance or transmittance. d. A benchtop where you can select the material being measured and adjust its concentration. 3. Go ahead and click around for a while, to see what all the buttons do in the simulation. When you are finished exploring, set the simulation for the following settings: a. In the benchtop, select the drop-down arrow to replace "drink mix" with NiCl₂. The concentration of 100 mm (millimolar) is OK. The cuvette should be filled with a green solution. b. Set the wavelength to "Variable." Start the wavelength at 780 nm by either clicking the arrows, or by dragging the bar. c. Set the meter to measure "Absorbance." 4. Switch on the light by pressing the red on-button. Notice that the meter is measuring how much light passes through the cuvette with its sample of green NiCl₂ solution. 5. Set the wavelength (780 nm) and observe the absorbance value. Verify that the absorbance value you obtain is about 0.21. The absorbance is a measure of the log of how much light gets through the sample (I) compared to how much light was sent into the sample (Io): A = -log(). The instrument computes this value for you with each measurement. Because absorbance is a ratio of light in vs. light out, there are no units. 6. Decrease the wavelength to 760 nm and record the absorbance at this wavelength. Continue to make measurements in 20-nm increments to find the gross absorption spectrum. Once you have finished all available measurements, observe: which wavelength gave you the highest point on the spectrum? 7. Go to that region, and gather data over three 5-nm increments to each side of your highest point.² Record data collected in Part IV Data Collection Table 1. a. The object here is to map out the region to find the 2max to the closest possible wavelength. 8. Once you have found the highest absorbance for NiCl₂(aq), record both the absorbance value and the wavelength value. The wavelength value at the highest point is the max. 9. Graph this data using Excel with absorbance on the y-axis and wavelength (nm) on the x-axis. From the graph, verify that the value you selected for max matches the curve. 2 For example, if the highest point in your roughed-out absorption spectrum occurred at 650 nm, take measurements in 5- nm hops at 635, 640, 645 (15 nm below 650) and at 655, 660, and 670 (15 nm above 650).

IV. Data Collection Part 1: Generate the absorption spectrum and find 2max for a solution of NiCl₂(aq) Table 1. Absorbance of NiCl₂ solution (you may add more rows if necessary) Wavelength Absorbance 760 (745,750, 755 <-> 765,770,775) 740 720 700 680 660 640 Insert graph here: 0.22 0.21 0.19 0.19 0.16 0.11 0.07 Report the value you chose for the 2max for a solution of NiCl₂(ag). Explain why you chose this value for 2max. Use complete sentences.

10. Insert the graph in Part IV Data Collection. Part 2: Creating a Standard Curve 1. Return to the simulation: Explore the variables €, b, and C for Beer's Law by playing with the simulation. You have already worked with the light source. Have you tried changing the path length (width) of the cuvette yet? Also, change the kind of material that is being measured. Each material has its own € in Beer's Law. 2. Back to the Beer's Law simulation. Let's set up for this work. a. Selected the NiCl₂ material. b. Set the cuvette width to 1 cm. c. Set the wavelength to the max value that you found in your earlier work. You will use this wavelength to measure the absorption of a series of NiCl₂(aq) solutions. 3. Notice that the concentration of the solutions we are working with are given in mM, millimolar. This translates to millimoles per liter of solution. Slide the concentration for the NiCl₂ solution to 0 MM. Record the absorbance for this solution. Now add material to the cuvette in 25-mM jumps, and record the absorbance for each. Continue measuring the absorbance for each 25- mM step until you have reached 300 mm. 4. Fill out Part IV Data Collection Table 2 which should include absorbance values for 13 different concentrations of green NiCl₂(aq) solution. 5. Prepare a graph using Excel. You should constrain the equation of the line to go through the origin (0, 0) if you can. Be sure to d. Plot absorbance on the y-axis and concentration of the x-axis; e. Draw the line of best linear fit for the data; f. Find and report the value r².3 g. Find and report the equation of the line as y = mx + b; display the equation on the graph. h. Express the equation of the line in terms of Beer's Law (i.e. replace y with A, m with e- b, and x with C). So if your equation of the line is y = 12x + 0.000, that would mean that your Beer's Law line has y = A; slope 12 L/mmol = b; and x = C, so you would write A = 12,000 L/mol · C. - Important! In this simulation, b = 1 cm, and C is in units of mM. i. Find and report the value for e, taking into account that slope = €-b. 6. Insert the graph to Part IV Data Collection 7. Use Beer's Law (the equation of the line) to complete Part IV Data Collection Table 3. Show all calculations. Report the answer to the correct number of significant figures, and use units in your calculation, (that is, all numbers keep their units in the calculations; and you manipulate units in the calculation as needed). Problem a has been completed as a model.

Table 2. Data Collected for Beer's Law Experiment Concentration, mM 0 25 50 75 100 125 150 175 200 225 275 300 Insert graph here: Report r² for the equation of the line. Report the value and units for e. Absorbance 0 0.5 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 Table 3. Using Standard Curve to find unknowns Problem Concentration a b C d 80 mM 180 mM Absorbance 0.43 0.75 1.29 Show your calculations and solution for problems (b) and (c). Applied Exercises QUANTUM NUMBERS & ELECTRON CONFIGURATION: Answer questions in COMPLETE sentences. 1. Give the electron configuration for the following atoms using appropriate noble gas inner core abbreviation: V. Bi Sr P 2. Give a set of 4 possible quantum numbers for the most energetic electron(s) of: Bi Cr Sr P n = I Ï = m₁ = 02= 3. What is the symbol and name of the element with the following electron configuration? Symbol [kr]5s24d105p² [Xe]6s¹ [6]4s¹3d10 4. What is the symbol and name of an element that could have the following n and I quantum numbers to describe its most energetic electron? Symbol 4 1 5 2 Name 20 5,3 Name