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This exam involves using absorbance spectrum to analyze a Co?" unknown solution. Multiple working standard solutions will be prepared by diluting a stock solution of Collze The 0.200M stock solution will be the highest concentration standard; it has been analyzed to give the table (below) of absorbances as a function of wavelength. This analysis will be done by spectrophotometry. Measurements are done in 1.20cm cuvettes. The stock solution, glassware, and the spectrophotometer are provided. Everything else is your responsibility. Submit your answers onto blackboard, I Plot an absorption spectrum. Submit the graph to this exam, following this sheet of paper. You can use excel to create this graph. Locate the wavelength value of maximum absorbance. Indicate this wavelength on the graph and record the value below. Wavelength Absorbance (nm) 400 0.026 420 0.130 440 0.233 460 0.414 480 0.672 500 0.843 520 0.918 540 0.704 560 0.374 580 0.172 600 0.104 620 0.078 640 0.050 Amox- nm. (5) From the absorption spectrum, calculate the value of the molar absorptivity coefficient for the solution (5) If you change the concentration of the solution above, will the molar absorption coefficient change? Why? (5)

Dilutions for the lab. For this lab you need to create five dilutions. In the chart below, I have provided you with the five dilution concentrations. To create the dilutions, you are provided with 50,0 mL of 0.200M cobalt chloride stock solution. Use your beers law equation to help answer the data table below. Fill in the missing information. Show your work. Dilution Concentration (M) Absorbance for each solution 0.180 0.150 0.120 0.0900 0.0600 Use the concentrations and absorbance in the above chart, in the chart on page 3 also.

Unknown Concentration and Absorbance: At the end of the lab, you will find your unknown information. Use this information to find your specific unknown absorbance. Record the information in the space below. Use the sample dilutions, from above (page 2), to calculate a known beer's law graph. Record your concentrations and their absorbances below. Solution Absorbance Create a graph comparing the known solution Concentration concentration and absorbance, Use this graph to OM (blank) calculate the Unknown concentration (C#1). Attach your graph on blackboard. (10) Unknown code: A[from table on last page) C#1 = When finished, all your working standard solutions are to be placed in the waste container Perform the best linear regression using Graphing calculator or Excel and report your regression equation in terms of the variables studied. Include the value of R. Equation R? Using your regression equation calculate the concentration of your unknown. Show your calculation below. (5) C#2= Using your regression equation, Beer's Law, and only necessary information that is common to all your trials, calculate the value of the molar absorption coefficient. Show your calculation (5)

Conclusion: During your calculations did you recognize any type of error? Provide reasoning why. Post Lab Questions: 1 An amine complex of cobalt (III) is yellow-orange and has a Deox of 475 nm. The standard curve below is for a set of standards measured at du in a 1.8 cm cell. Use it to answer the questions that follow. 0.8 0.7 0.6 0.5 Absorbance 0.4 0.3 02 0.1 0 0 0.05 0.1 025 0.15 02 Concentration CM 03 a Suppose you ran the same samples in a 1.2 cm cell. Explain, if any, changes in: i Absorbance - ii. Concentration - iii Molar absorptivity b. Your classmate runs the same set of standards at 500 nm. Explain how the data will change and how the graph above will look