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Lab Manual Experiment 4A

Lab Manual Experiment 4A - EXPERIMENT 4A Synthesis of an...

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Experiment 4A- Page 1 EXPERIMENT 4A Synthesis of an Iron (III) Oxalate Complex In this experiment, you will synthesize a coordination compound in which iron (III) coordinates with oxalate ion, the anion of a diprotic organic acid. After isolating and purifying the compound, you will analyze it for its composition of oxalate (Experiment #4B) and iron (Experiment #4C) using two different analytical chemistry techniques: oxidation- reduction titration and spectrophotometry. Based on the results of your analyses, you will then be able to calculate the empirical formula of the compound. INTRODUCTION A coordination compound has at least one complex ion (and often more than one). A complex ion consists of two parts: a metal ion (usually a transition metal) and ligands. The metal ion typically carries a +2 or +3 charge in an aqueous solution. Such metal ions tend to be electron deficient (i.e., they are Lewis acids). A ligand is a molecule or anion that can donate an electron pair (i.e., it is a good Lewis base) to the metal ion. Water and ammonia molecules are examples of neutral species that can act as monodentate ligands, those that donate a single pair of electrons to the metal ion to form a complex ion. Each has a lone pair of electrons on the central atom which can coordinate with the metal ion. Anions such as chloride or cyanide are also electron-rich and are good monodentate ligands. Commonly, 2, 4 or 6 electron pairs from the ligands will coordinate to a metal center depending on the particular ligand and metal involved. The number of electron pairs donated to the metal center is known as the metal's coordination number . For examples, the complex ions [Ag(NH 3 ) 2 ] + , [Cu(CN) 4 ] 2 , and [Fe(H 2 O) 6 ] 3 + have 2, 4 and 6 monodentate ligands, respectively, each ligand donating an electron pair, and coordination numbers of 2 (for Ag + ), 4 (for Cu 2+ ) and 6 (for Fe 3+ ). A complex may have an overall charge that is positive, negative, or even zero. Some ligands such as the oxalate anion have two coordination sites (electron-pairs) available for a metal ion, one at each end of the ion: Oxalic acid Oxalate ion The oxalate ion is said to be bidentate because it can bond at two sites around the metal instead of simply one (thus, Fe (C 2 O 4 ) 2 has a coordination number of four, not two!). The general term used to describe ligands which bind at more than one site (i.e., multidentate) is chelate (from the Greek word for claw). Oxalate binds quite readily with the Fe (III) ion. We will synthesize the iron (III) oxalate complex and precipitate it as the potassium salt with the general formula K w [Fe x (C 2 O 4 ) y ] z H 2 O. The whole-number values of w , x, y , and z will be determined in Experiments #4B & 4C. In this experiment, you will synthesize, isolate and purify the K w [Fe x (C 2 O 4 ) y ] z H 2 O salt product.
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Experiment 4A- Page 2 PRELABORATORY QUESTIONS 1. Balance the reaction taking place in Step #2 of this experiment: _ Fe (NH
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Lab Manual Experiment 4A - EXPERIMENT 4A Synthesis of an...

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