Question

10. Chromate and permanganate can be determined in the same sample by absorbance spectroscopy. Chromate absorbs strongly at 440 nm while permanganate absorbs better at 525. A standard containing 0.01 M KMnO4 and one containing 0.02 M K2Cr207 are prepared and their absorbances are measured at both wavelengths. The sample containing the two analytes is also read. The following data are obtained. What is the concentration of permanganate and dichromate in the sample?

Answer 1

Here we are giveer absorbance of known concentrations of kmnou, k₂cr of at 440 um and 525 um. The unknown following sample containing both king, and Kqcroy has the absorbances. I solution A440 | A525 | 0.01M Km not (x) 0.0094 0.442 0.02M KyCr2O7(Y) 0-320 0.0039 Sample (x+y) 0.17€ 10-380 for Kunoy (x): 0.0094 = K440,x(0.01) > *440x = 0.947 0.442 = *525,x (001) >> K$25,x = 44.2 → For K, CV, O2(4): 0.320 = kq4o y(0.02) K440,7 = 16 6.0039 = K525,y (0.02) = K525, y = 0.195) This generates two simultaneous equations A440 = $440x (Cx) + K 440,X (C) & A325 = k025, ccx) + 352, (4) substituting and solving and gives the concentrations of km no (cx) and K₂cr₂O7 (24) in the sample (aty). 0.177= 0.94 Cx + 16 Cy $ 0.380 = 44.2 Cx + 0.197 Cy → Cx = [kmnou] = 0.0087 ; Cy = [KC5,04] - 0.0066 ③ for all these measurement same experimental settings were used so the length of the cell is same for all measurements. so, it can be considered a constant and could be combined with molar absorbances. = Absorbance (A) = KC where ci concentration.