CHE134 Summer Lecture 6

CHE134 Summer Lecture 6 - NK LA B CH CH2 N Fe N N N CH3 CH...

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COLORIMETRIC DETERMINATION OF IRON IN MULTIVITAMINS & AN UNKNOWN TEST EXERCISE (105 pts) Obj10 A = * b c BLANK N N N N H 3 C CH CH 2 CH 3 CH CH 2 CH 3 CH 2 CH 2 COOH CH 2 HOOCCH 2 H 3 C Fe LAST
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Objective: Determine weight of iron in a multivitamin pill and concentration of iron in an unknown solution - colorimetrically Concepts: Complexation Volumetric Dilution Oxidation-Reduction Buffers Beer’s Law Techniques: Preparing precise dilutions and related calculations Using Spectrophotometer Apparatus: Spectronic 20 Volumetric Flask Pipet
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BACKGROUND - Fe, AN ESSENTIAL NUTRIENT Constituent of HEME N N N N H 3 C CH 2 3 2 3 2 2 COOH 2 HOOCCH 2 H 3 C Fe
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1. Some form reversible complexes with iron, the main function of which is iron transport and storage ferritin / transferrin 2. Some are able to bind oxygen reversibly - hemoglobin ( Hb + 4O2 Hb(O2)4 ) 3. Some are metallo-enzymes, in which iron performs a catalytic role - ferredoxin Found in MYOGLOBIN and HEMOGLOBIN and other metalloproteins: contains 4500 Fe3+ ions
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COMPLEXATION Complexing agent - 1,10-Phenanthroline Nomenclature: N N Benzene Naphthalene Anthracene Phenanthrene 1,10 Phenanthroline
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Stoichiometry of complex is 3 : 1 i.e., 3 mol of 1,10-Phenanthroline react with 1 mol of Ferrous Ion (Fe+2) Fe2+ Analytical Wavelength (Absorbance maximum) is at 508 nm The complex is red-orange
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Stoichiometry of complex is 3 : 1 i.e., 3 mol of 1,10-Phenanthroline react with 1 mol of Ferrous Ion (Fe+2) Analytical Wavelength (Absorbance maximum) is at 508 nm 1,10-Phenanthroline complex requires that IRON be in the +2 STATE NOT Fe3 + The complex is red-orange Fe2 + - NOT +3
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OXIDATION – REDUCTION CHEMISTRY Add REDUCING AGENT - HYDROQUINONE Procedure requires MILDLY ACIDIC environment. ( pH 3.0 – 3.5 ) Hydroquinone OH OH O O + 2H + Quinone + 2e - + 2 Fe3+ 2 Fe2+ electron donor
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BUFFERS Use Sodium Hydrogen Citrate Buffer . CITRIC ACID is a weak triprotic acid with ionization constants (H3Cit): K1 = 8.2 X 10-4 pKa = 3.09 K2 = 1.77 X 10-5 4.75 K3 = 3.9 X 10-6 5.41 Its partially neutralized salts (NaH2Cit, Na2HCit) are natural buffers over a range of acidic pH’s C C C H H C H H C O O O C O H O O H H H O Na Na
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PROCEDURE Obtain ~50 mL of iron stock solution BEER’S Law Rinse buret with iron stock solution before preparing dilutions Prepare a BLANK solution BLANK solution must contain Work IN PAIRS
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This note was uploaded on 01/09/2011 for the course CHE 134 taught by Professor Staff during the Summer '08 term at SUNY Stony Brook.

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CHE134 Summer Lecture 6 - NK LA B CH CH2 N Fe N N N CH3 CH...

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