Potassium dichromate and potassium permanganate have overlapping absorption spectra in 1M H2SO4 . K2Cr2O7 has an absorption maxima at 440 nm, and KMnO 4 has a band at 545 nm (the maximum is actually at 525 nm, but the longer wavelength is generally used where interference from K2C2O7 is less). A mixture is analyzed by measuring the absorbance at these two wavelengths with the following results: A 440 =0.405, A 545 =0.712 in
Potassium dichromate and potassium permanganate have overlapping absorption
spectra in 1M H2SO4 . K2Cr2O7 has an absorption maxima at 440 nm, and KMnO 4 has a band at 545
nm (the maximum is actually at 525 nm, but the longer wavelength is generally used where
interference from K2C2O7 is less). A mixture is analyzed by measuring the absorbance at these two
wavelengths with the following results: A 440 =0.405, A 545 =0.712 in a 1-cm cell. The absorbances of
pure solutions of K2Cr2O7 (1x10 -3 M) and KMnO 4 (2.00x10 -4 M) in 1 M H 2 SO 4 , using the same cell gave
the following results: A Cr,440 = 0.374, A Cr,545 = 0.009, A Mn,440 =0.019, A Mn,545 = 0.475. Calculate the
concentrations of dichromate and permanganate in the sample solution.
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