Iron(II) ions catalyze the oxidation of luminol by H2O2. The intensity of the re

Question

Iron(II) ions catalyze the oxidation of luminol by H2O2. The intensity of the resulting chemiluminescence has been shown to increase linearity with iron(II) concentration from 10–10 to 10–8 M. Exactly 1.00 mL of water was added to a 2.00-mL aliquot of an unknown Fe(II) solution, followed by 2.00 mL of a dilute H2O2 solution and 1.00 mL of an alkaline solution of luminol. The chemiluminescence from the mixture was integrated over a 10.0-s period and found to be 12.6. To a second 2.00-mL aliquot of the sample was added 1.00 mL of a 3.58×10–5 M Fe(II) solution followed by the same volume of H2O2 and luminol. The integrated intensity was 30.4. Find the concentration of Fe(II) in the sample in M.

Explanation / Answer

molarity of Fe(II) standard in total solution = 3.58 x 10^-5 x 0.001/0.003 = 1.19 x 10^-5 M

It gave an inensity of 30.4

Sample intensity = 12.6

So, the concentration of Fe(II) sample in total volume = 1.19 x 10^-5 x 12.6/30.4 = 4.93 x 10^-6 M

molarity of Fe(II) in the original sample = 4.93 x 10^-6 x 0.006/0.002 = 1.48 x 10^-5 M

Thus concentration of Fe(II) in the sample = 14.8 microM

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