AP Chemistry Lab 11 QiTong Han March 21, 2015 The Determination of an Equilibrium Constant Purpose Determine the value of equilibrium constant, K eq , for the reaction by using the determined molar concentrations of the ions present at the equilibrium. Procedure 1. Obtain and wear goggles. 2. Label five 100 mL beakers 1-5. Obtain small volumes of 0.200 M Fe(NO 3 ) 3 , 0.0020 M SCN – , and distilled water. CAUTION: Fe(NO 3 ) 3 solutions in this experiment are prepared in 1.0 M HNO 3 and should be handled with care. Prepare four solutions according to the chart below (The fifth beaker is a blank.). Use a 10.0 mL pipet and a pipet pump or bulb to transfer each solution to a 50 mL volumetric flask. Mix each solution thoroughly. Measure and record the temperature of one of the above solutions to use as the temperature for the equilibrium constant, Keq. Beaker number 0.200 M Fe(NO 3 ) 3 (mL) 0.0020 M SCN – (mL) H 2 O (mL) 3. Connect the Colorimeter to the computer interface. Prepare the computer for data collection by opening the file “10 Equilibrium” from the Advanced Chemistry with Vernier folder of LoggerPro 4. Prepare a blank by filling a cuvette 3/4 full with distilled water. 5. Open the Colorimeter lid, insert the blank, and close the lid. 6. Calibrate the Colorimeter and prepare to test the standard solutions. a. Press the < or > button on the Colorimeter to select a wavelength of 470 nm (Blue). b. Press the CAL button until the red LED begins to flash and then release the CAL button. c. When the LED stops flashing, the calibration is complete. d. Empty the water from the blank cuvette. Using the solution in Beaker 1, rinse the cuvette twice with ~1 mL amounts and then fill it 3/4 full. Wipe the outside with a tissue, place it in the Colorimeter. 7. Collect absorbance-concentration data for the five standard equilibrium mixtures. a. Leave the cuvette, containing the Beaker 1 mixture, in the device (Colorimeter or Spectrometer). Close the lid on the Colorimeter.) b. Click . Click , type the concentration of FeSCN 2+
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