General Chemistry Synthesis and Characterization of Cobalt Lab

General Chemistry Synthesis and Characterization of Cobalt Lab

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Synthesis and Characterization of [Co(NH 3 ) 4 CO 3 ]NO 3 Introduction In this experiment, the main goal is to study the formation and properties of a coordination compound. A coordination compound is composed of a central atom bound to multiple groups called ligands. There is a wide variety of possible ligands that can bond directly to the central atom, but only two common ones, NH 3 and CO 3 , are to be studied in this particular experiment. In the formation of carbonatotetraamminecobalt (III) nitrate, denoted [Co(NH 3 ) 4 CO 3 ]NO 3 , the transition metal which serves as the central atom is cobalt. Its first coordination sphere, or everything directly bonded to the cobalt, is four nitrogen atoms and two oxygen atoms. This coordination sphere is represented in the chemical formula with brackets. Because cobalt is involved in six bonds, its coordination number is six, and the structure around the cobalt is octahedral. It is apparent where the four nitrogen atoms come from, since there are three ammonia molecules in the formed complex. However, there is only one carbonate molecule. This ligand is called a bidentate ligand because two of its atoms were bonded to the metal. Thus, the ammonia ligands are all monodentate ligands because only one of their atoms was bonded to the metal. Because the first coordination sphere does not break apart in aqueous solution, it is considered a separate ion like NO 3 . The charge of the cobalt octahedron, called a complex ion, is +1 and the charge of the nitrate is -1. It can therefore be determined that cobalt had a charge of +3. Since the cobalt nitrate that will be used in the synthesis of the coordination compound has a charge of +2, the cobalt loses an electron and is oxidized. Hydrogen peroxide is used as the oxidizing agent, so it is reduced to water. The formation of the coordination compound is a redox reaction, and the equation can be balanced using half-equations. The balanced equation is shown below: 2Co(NO 3 ) 2 + 6NH 3 + 2(NH 4 ) 2 CO 3 + H 2 O 2 2[Co(NH 3 ) 4 CO 3 ]NO 3 + 2NH 4 NO 3 + 2H 2 O Theoretically, carbonatotetraamminecobalt (III) nitrate is formed, but further analysis of the coordination compound will be necessary to validate this assertion. The complex will be characterized in terms of absorbance, conductivity, magnetic susceptibility, and infrared spectroscopy. The Beer’s Law equation A = εlC can be used to calculate the mass of carbonatotetraamminecobalt (III) nitrate needed to prepare a solution of which the absorbance reading will be 0.6. Once the absorbance spectrum is obtained, Beer’s Law can also be used to calculate the molar
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absorptivity or extinction coefficient by substituting lambda max for A. In this equation, A is absorbance, ε describes how well the compound absorbs light, l is the path length, and C is the concentration.
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General Chemistry Synthesis and Characterization of Cobalt Lab

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