Lab 2 - Chem Eq. & Beer's Law
Objective:
To determine the concentration and equilibrium constant for a reaction of colored product using absorption spectroscopy, to create a calibration curve for determining equilibrium concentrations by applying Beer’s law and to force the completion of a reaction by applying Le Châtelier’s principle.
Procedure:
A diluted solution was made from the stock of 0.0025 M Fe(NO3)3 by diluting 4.0 mL to exactly 100.00 mL, using serological pipet and volumetric flask. The concentration of the diluted solution was calculated and recorded. The following known solutions were made up in labeled medium test tubes, using a serological pipet, mixing them thoroughly.
For Part A: Absorbance of {Fe(SCN)}2+ “Knowns”
Table 1: Solution Mixtures to determine Absorbance of {Fe(SCN)}2+ “Knowns.” Test Tube | Diluted Fe3+ (mL) | Stock 0.50 M KSCN (mL) | Stock of 0.1 M HNO3 (mL) | 1 | 1.0 | 5.0 | 4.0 | 2 | 2.0 | 5.0 | 3.0 | 3 | 3.0 | 5.0 | 2.0 | 4 | 4.0 | 5.0 | 1.0 | 5 | 5.0 | 5.0 | 0.0 |
For Part B: Absorbance of {Fe(SCN)}2+ “Unknowns” Test Tube | Stock 0.0025 M Fe(NO3)3 (mL) | Stock of 0.0025 M KSCN (mL) | Stock of 0.1 M HNO3 (mL) | 6 | 1.0 | 1.0 | 5.0 | 7 | 1.0 | 1.5 | 4.5 | 8 | 1.0 | 2.0 | 4.0 | 9 | 1.0 | 2.5 | 3.5 | 10 | 1.0 | 3.0 | 3.0 | 11 | 2.0 | 1.0 | 4.0 | 12 | 2.0 | 1.5 | 3.5 | 13 | 2.0 | 2.0 | 3.0 | 14 | 2.0 | 2.5 | 2.5 | 15 | 2.0 | 3.0 | 2.0 |
A Vernier SpectroVis Plus was attached to a LabQuest device to measure the absorbance. The spectrometer was calibrated with a cuvette filled with deionized water as a “blank.” The absorbance of the water and cuvette were stored in the spectrometer’s memory and subtracted from subsequent runs. An absorbance spectrum was acquired over the visible wavelength range of the most concentrated sample of {Fe(SCN)}2+. The cuvette was filled with the solution until ¾ full. The clear sides of the cuvette were cleaned after each use. The wavelength where the absorbance is at maximum, λmax was
To determine the concentration and equilibrium constant for a reaction of colored product using absorption spectroscopy, to create a calibration curve for determining equilibrium concentrations by applying Beer’s law and to force the completion of a reaction by applying Le Châtelier’s principle.
Procedure:
A diluted solution was made from the stock of 0.0025 M Fe(NO3)3 by diluting 4.0 mL to exactly 100.00 mL, using serological pipet and volumetric flask. The concentration of the diluted solution was calculated and recorded. The following known solutions were made up in labeled medium test tubes, using a serological pipet, mixing them thoroughly.
For Part A: Absorbance of {Fe(SCN)}2+ “Knowns”
Table 1: Solution Mixtures to determine Absorbance of {Fe(SCN)}2+ “Knowns.” Test Tube | Diluted Fe3+ (mL) | Stock 0.50 M KSCN (mL) | Stock of 0.1 M HNO3 (mL) | 1 | 1.0 | 5.0 | 4.0 | 2 | 2.0 | 5.0 | 3.0 | 3 | 3.0 | 5.0 | 2.0 | 4 | 4.0 | 5.0 | 1.0 | 5 | 5.0 | 5.0 | 0.0 |
For Part B: Absorbance of {Fe(SCN)}2+ “Unknowns” Test Tube | Stock 0.0025 M Fe(NO3)3 (mL) | Stock of 0.0025 M KSCN (mL) | Stock of 0.1 M HNO3 (mL) | 6 | 1.0 | 1.0 | 5.0 | 7 | 1.0 | 1.5 | 4.5 | 8 | 1.0 | 2.0 | 4.0 | 9 | 1.0 | 2.5 | 3.5 | 10 | 1.0 | 3.0 | 3.0 | 11 | 2.0 | 1.0 | 4.0 | 12 | 2.0 | 1.5 | 3.5 | 13 | 2.0 | 2.0 | 3.0 | 14 | 2.0 | 2.5 | 2.5 | 15 | 2.0 | 3.0 | 2.0 |
A Vernier SpectroVis Plus was attached to a LabQuest device to measure the absorbance. The spectrometer was calibrated with a cuvette filled with deionized water as a “blank.” The absorbance of the water and cuvette were stored in the spectrometer’s memory and subtracted from subsequent runs. An absorbance spectrum was acquired over the visible wavelength range of the most concentrated sample of {Fe(SCN)}2+. The cuvette was filled with the solution until ¾ full. The clear sides of the cuvette were cleaned after each use. The wavelength where the absorbance is at maximum, λmax was