05MANanalysisfe - Analysis of a Complex Iron Salt Revised...

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Analysis of a Complex Iron Salt Revised 5/06/08 1 ANALYSIS OF A COMPLEX IRON SALT OBJECTIVES For you, the student, to write…. SAFETY PRECAUTIONS Safety goggles, aprons, and gloves must be worn at all times in the laboratory. H 2 SO 4 and concentrated H 3 PO 4 are corrosive acids; wash all affected areas thoroughly with cold water. Acetone and alcohol are flammable reagents; extinguish any open flames or spark sources in the lab. Sodium oxalate is very toxic via oral and inhalation routes and severe kidney damage is possible if oxalate salts are taken internally. Oxalate compounds can be absorbed through the skin; wear gloves and wash affected areas with cold water. KMnO 4 is a very strong oxidizing agent; do NOT pour any permanganate solutions into the ORGANIC collection bottles. Permanganate solutions can stain skin and clothing. INTRODUCTION The complex iron salt prepared in a previous experiment is known to contain potassium, iron (III), oxalate, and loosely bound waters of hydration. The general formula is: K x Fe y (C 2 O 4 ) z . n H 2 O. The mass percent oxalate ion in the salt will be determined by titration with a standardized KMnO 4 solution as shown in the unbalanced reaction below: (1) MnO 4 (aq) + C 2 O 4 2– (aq) Æ Mn 2+ (aq) + CO 2 (g) Since aqueous solutions of permanganate ion are not stable over a long period of time, the exact concentration of KMnO 4 must be determined by titration with a known amount of a primary
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Analysis of a Complex Iron Salt Revised 5/06/08 2 standard salt such as sodium oxalate, Na 2 C 2 O 4 . After KMnO 4 has been standardized, the complex iron salt can be titrated to determine its oxalate content. The solutions containing C 2 O 4 2– and Mn 2+ ion are colorless; the MnO 4 solution is a deep purple color. Therefore, the titrated solution will remain colorless until all the oxalate salt is consumed in the reaction. The endpoint corresponds to the appearance of the first permanent pink color due to the presence of excess unreacted permanganate ion. The rate of the reaction is very slow at room temperature so the solution must be heated to 80°C to observe the color change in "real time". Often there is a 30-60 second time lag at the beginning of the titration before the color changes begin to take effect because the reaction takes place in a series of steps and an intermediate must be formed before the reaction goes to completion. Interferences can occur in redox titrations from impurities in the solvent which act as reducing or oxidizing agents. Corrections are easily made by titrating a "blank" containing only the solvent. The "corrected volume" is equal to the volume of KMnO
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This note was uploaded on 11/23/2010 for the course CHEMISTRY Chem 1LC taught by Professor Dr.kimberlyedwards during the Fall '10 term at UC Irvine.

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05MANanalysisfe - Analysis of a Complex Iron Salt Revised...

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