Lab 4: Spectrophotometric Analysis of Copper lon Solutions Record all measured data and calculated data with the correct

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Lab 4: Spectrophotometric Analysis of Copper lon Solutions Record all measured data and calculated data with the correct number of significant figures and with correct units. Part 1: Determining Wavelength of Maximum Absorbance 1. Describe the solution concentrations and the wavelengths of maximum absorbance for both the copper(11) sulfate and the cobalt(II) chloride solutions. Also record the absorbance value at the wavelength of maximum absorbance for each solution. Solution Concentration (M) Wavelength... (nm) Absorbance CUSO Coch 2. (a) Compare the color of each solution to the color of the wavelength of light that is absorbed most effectively-shown by the wavelength of maximum absorbance. For each solution, explain how the colors relate to one another on the color wheel shown in the background. (b) Explain your answer to 2(a) in terms of "light absorbed" vs. "light reflected by the solution. Part 2: Developing a Standard Curve from Known Concentrations 3. Show your work for calculating the concentration of CuSO, in the solutions in Flasks 1-4. These are dilution calculations (reference Section 4.5 in the ebook). Include units on all values used in your calculations and remember to report calculated values with correct significant figures and units. Flask 1:1 Flask 2: Flask 3: Flask 4:

4. Complete the Table by entering your calculated Cu" ion concentrations (same as the CuSO, concentrations in previous question) and the Absorbance measurements for those solutions. Remember Solution 5 is the undiluted copper ion solution. Solution Cu ion Concentration (M) Absorbance 1 2 3 4 5 5. Record the wavelength you used to measure the absorbance values in the above table? Remember units! 6. Using Excel or another graphing program, create a graph of absorbance (A) as a function of the copper (11) concentration (M) for each of the five known standard solutions you prepared. Your graph should include: Visible data points and the best fit line. Labeled axes with appropriate labels including units. Your graph is called a calibration plot (or standard curve) because it provides a relationship between absorbance and concentration for aqueous solutions of this compound, specifically the Cu¹ ion. [Insert Graph image here] 7. Did you get a straight line? Explain, using Beer's Law described in the Background, why you would expect your data to produce a straight line.

Part 3: Using a Standard Curve to Determine Unknown Concentration 8. Determine the copper ion concentrations in your two unknown samples from the calibration plot you created in Part 2. To do this, find the concentration that matches the measured absorbance of each sample. (One way is to draw a line vertically from concentration to the line connecting the data points, and then draw a line horizontally from the graph to the y-axis. Another way is to use the equation of the line you generated.) Complete the following table. Be sure to record the absorbance measured and the molarity concentration determined from your calibration plot. Solution Absorbance Concentration (M) Measured Soln Wavelength used (am) Unknown #1 Unknown #2 9. Explain the method you chose for determining the concentration results in the previous question. 10. Suppose your spectrophotometer broke after creating the calibration plot, and you had to use a different one that required a wider cuvette to hold the sample. (a) Would you expect the absorbance measured for a given sample to be greater than, less than, or the same as the absorbance measured using the previous spectrophotometer? Explain your answer. (b) Would you have to create a new calibration plot using your copper ion solutions of known concentration to determine the concentration of the unknown? Explain your answer.