Potassium dichromate and potassium permanganate have overlapping absorption spectra in 1M H2SO4. K2Cr2O7 has an absorption maximum at 440 nm, and KMnO4 has a band at 545 nm (the maximum is actually 525 nm, but using the longer wavelength is advantageous because interference from K2Cr2O7 is less). A mixture is analyzed by measuring the absorbance at these two wavelengths with the following results: A440= 0.405, A545= 0.712 in a 1-cm cell (actually as long as all the measurements are made in the same cell, for problems such as this, the exact pathlength cancels out in the calculations). The absorbance of pure solutions of K2Cr2O7 (1.00x10-3M) and KMnO4 (2.00x10- 4M) in 1 M H2SO4, using the same cell gave the following results: ACr2O7,440= 0.374, ACr2O7,545= 0.009, AMnO4,440= 0.019, AMnO4,545= 0.475. Calculate the concentrations of dichromate and permanganate in the sample solution.
Potassium dichromate and potassium permanganate have overlapping absorption spectra in 1M H2SO4. K2Cr2O7 has an absorption maximum at 440 nm, and KMnO4 has a band at 545 nm (the maximum is actually 525 nm, but using the longer wavelength is advantageous because interference from K2Cr2O7 is less). A mixture is analyzed by measuring the absorbance at these two wavelengths with the following results: A440= 0.405, A545= 0.712 in a 1-cm cell (actually as long as all the measurements are made in the same cell, for problems such as this, the exact pathlength cancels out in the calculations). The absorbance of pure solutions of K2Cr2O7 (1.00x10-3M) and KMnO4 (2.00x10- 4M) in 1 M H2SO4, using the same cell gave the following results: ACr2O7,440= 0.374, ACr2O7,545= 0.009, AMnO4,440= 0.019, AMnO4,545= 0.475. Calculate the concentrations of dichromate and permanganate in the sample solution.
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