Cu Lab Summary

1. Prepare 10.0 mL of diluted CuSO4 solutions with the concentrations for trials 1-4. Transfer 35 mL of 0.040 M CuSO4 solution to a 100 mL beaker and label 15x150 mm test tubes with numbers 1-4 for each of the trials.
2. Use a plastic pipet to add either 0.040 M CuSO4 solution or H2O to a 10 mL graduated cylinder. Place the correct solution into each test tube and mix.
3. Fill a cuvette ¾ full with deionized water. This is your “reference blank”.
4. Turn on LabQuest and plug the spectrophotometer in.
5. Calibrate the spectrometer.
6.  After calibration is complete, place  the "reference blank" cuvette into the spectrophotometer.
7.  Select Finish Calibration. Remove  and empty the "reference blank" cuvette.
8. Fill the cuvette ~3/4 full with the 0.005 M CuSO4 solution and place it in the spectrophotometer.
9.  Start and after 5 seconds, stop.
10. Select the Mode menu and select "Events with Entry". enter Concentration For the Name and mol/L for the Units. Using the Table menu select “Data Column Options”. Select “Concentration”. Set the Decimal Places to 4.
11.  Use the meter screen and change the wavelength to 674.
12. Select start and type 0.0050 in the concentration box. The data point that you just collected should now appear on the graph.
13. Rinse a cuvette twice with the Test Tube 2 solution, 0.010 M CuSO4 , and fill the cuvette ¾    full. Place the cuvette in the spectrophotometer compartment, type “0.010” in the concentration box, and click OK.
14.  Repeat Step 12 for the other three samples. measure the absorbances for all the samples and then hit stop to end data collection.
15. choose Curve Fit, Abs from the Analyze menu. select the Fit Equation menu and select Linear. Record the slope (m) and the intercept (b) in your lab notebook.
16. Your data points should lie on, or very near, the regression line.
17.  Get 20 mL of the unknown Cu2+ solution you have been assigned.
18. Fill a cuvette ¾ full with the Cu2+ unknown solution and select the meter window. Place the cuvette into the spectrometer compartment and record the absorbance value.  
19. Unplug the LabQuest device and Save a copy of your data to a USB.
20. Discard your solutions, turn off labQuest and clean your materials and area.
21. Using Logger Pro open the experiment file and create a graph of absorbance v concentration with a regression line and print a copy.
22. Calculate the molar the concentration of Cu2+ in the unknown solution in your lab notebook.

Part II. Iodometric Redox Titration of Cu2+

1. Measure out 10.0 mL of the same unknown Cu2 solution you used in part I in a small graduated cylinder and place it in a 250 mL erlenmeyer flask. Add 10 mL of 0.20 M KI solution. Allow the mixture to sit for 5 minutes but swirl it several times during this time.

2. Add 50 mL of deionized water. swirl. Add 15 drops of starch indicator. swirl once again.

3. Pour the 0.025 M Na2S2O3 solution into a 25 mL buret and record the volume and place a piece of white paper under the flask. Swirl the flask continuously while you begin titration until when the dark color of the solution disappears.