(a) The pH of a 5.00 mL of a 100-ppm iron (II) is adjusted to pH 4.0 with an app
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Question
(a) The pH of a 5.00 mL of a 100-ppm iron (II) is adjusted to pH 4.0 with an appropriate buffer and an excess of 1, 10-phenanthroline was added. An orange-colored complex forms, in which each iron (II) ion is complexed with 1, 10-phenanthroline. The volume of the reaction is made up to 100.00 mL with deionized water. The transmittance of the resulting solution was 37.6% T at 540 nm in a 1.2 cm path-length cuvette. Calculate the molar of the complex. (Assume that formation constant of the complex is sufficiently large the reaction is complete).Explanation / Answer
Concentration of complex in solution = 100 ppm x 5 ml/100 ml
= 5 ppm
= 5/55.845 x 1000
= 8.95 x 10^-5 M
Absorbance = 2 - log(%T)
= 2 - log(37.6)
= 0.425
molar absorptivity of complex = absorbance/path length x concentration
= 0.425/1.2 x 8.95 x 10^-5
= 3957.17 M-1.cm-1
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