Colorimetric Determination of Keq Experiment 22 Colorimetric Determination of Keq CHE118

In Lab Work in groups of 4 2 people do part A; preparing the standard solutions 2 people do part B; preparing the solutions at equilibrium Everyone makes their own calibration curve CHE118

Part A Standards for the Calibration Curve Reation is “forced” to the product side, assume no equilibrium Prepare all solutions at the same time Use correct Fe solution (2.00x10-1 M) Flask 1 (solution 1) is blank (no SCN) Use 0.10 M HNO3 to prepare solns., not water Use disposable test tubes instead of cuvettes for use in the spectrophotometer CHE118

Part B Preparation of Equilibrium Solutions Prepare all solutions at the same time Use the correct Fe solution (2.00x10-3 M) Prepare a blank solution (5.00 mL Fe, no SCN, no H2O) Use 0.10 M HNO3 to prepare solns., not water. Use disposable test tubes instead of cuvettes for use in the spectrophotometer CHE118

Spectrophotometer (Parts A and B) An instrument that will indicate the amount of light (of one wavelength) absorbed by a sample readout detector sample monochromator Light source slit LED readout CHE118

Making the Calibration Curve You will acquire an absorbance reading for each standard solution prepared (share data) Use the data from Part A to construct the calibration curve CHE118

Calibration Curve Absorbance Concentration [FeNCS2+] x 10-5 M CHE118

Using the Calibration Curve to Find Equilibrium Concentration of FeNCS2+ Absorbance Concentration [FeNCS2+] x 10-5 M Part B solution absorbance reading Concentration of solution Show this on your graph CHE118

For All Students There are two different Fe(NO3)3 solutions; Part A uses a 2.00x10-1M solution, and Part B uses a 2.00x10-3M solution. The 0.10M HNO3 solution is added to test tubes 1 – 5, not 1 – 6 in part B (page 289), to get to a total volume of 10 mL in each test tube. CHE118