Synthesis and Analysis of the Coordination Compound Pentaaminechlorideocobalt (III) Chloride Heaven Lin and Forest Lin
W.M. Keck Science Department, Claremont McKenna, Pitzer, and Scripps Colleges 925 N. Mills Avenue, Claremont, California 91711
Through using the spectrometer and titrations, the amount of the coordination compound, pentaaminechloridocobalt (III) chloride, was determined through a synthesis through an oxidation reduction of cobalt (II) chloride hexahydrate (CoCl2·6H2O) and a reaction of the product with ammonium chloride (NH4Cl) and ammonia (NH3). Through iodometric and spectrophotometric analysis, the percent cobalt was then found in the samples of pentaaminechloridocobalt. When looking at the iodometric analysis, there was a mean amount of 26.29% cobalt with an average deviation of ± 1.00%. When looking at the spectrophotometric analysis, there was a mean amount of 15.30% cobalt with an average deviation of ± 2.00%. With a theoretical yield of 23.50%, the iodometric analysis proved to be more accurate than the spectrophotometric analysis.
Keywords: Pentaaminchloridocobalt, iodometric analysis, spectrophotometric analysis
In chemistry, the study of transition metals allows the scientist to witness coordination complexes form with ligands, such as a non-metal atom (electron donor). Another way of looking at the electron donor is as a Lewis base that is a compound or ionic molecule that can donate an electron pair to an acceptor molecule. In this experiment, the pentaamminechloridocobalt(III) ([Co (NH3)5Cl]2+) is synthesized and then analyzed through an iodometric and a spectrophotometric analysis to find the amount of cobalt in the solution. Through an oxidation reaction of synthesizing pentaaminechloridocobalt (III) chloride with cobalt (II) hexahydrate and hydrogen peroxide, and then reacting the product with ammonium chloride and ammonia, complexes are formed with the chloride and ammonia ions. The balanced equation described above is: 2 CoCl2·6H2O(s) + 2 NH4Cl(s) + 8 NH3(aq) + H2O2(aq) → 2 [Co(NH3)5Cl]Cl2(s) + 14 H2O(l). Using iodometric analysis, the known concentration of Na2S2O3 was titrated with the iodide that had been oxidized by the cobalt (III) to find the percent cobalt in the solution. The second method was through spectrophotometric analysis where Beer’s Law was utilized. According to Beer’s Law, the absorbance is equal to the log of 100 divided by the light transmitted (A=log()). All the wavelengths for this analysis were measured at 510 nm. To create a standardized Beer’s Law graph, five solutions of differing concentrations of cobalt (II) acetate tetrahydrate were measured and plotted on the graph, with the x-axis being the concentration of the cobalt, and the y-axis being the absorbance in nanometers. After the creation of the standardized graph, the sample collected was analyzed and compared through measuring the absorbance and plotting it with the standard graph.
In this lab, the materials needed are: analytical balance, sodium thiosulfate, deionized water, potassium iodate, weigh boats, 12M and 2M hydrochloric acid, 0.5% starch, pentaamminechloridocobalt(III), hot plate, 3M sulfuric acid, GoPro spectrometer, 50 mL volumetric flask, 100 mL beakers, 25 mL volumetric flask, 250 mL Erlenmeyer flasks, 14.8 M ammonia, 30% hydrogen peroxide, 95% ethanol, 100 mL graduated cylinder, timer, Buchner funnel, 2M sodium hydroxide, burette, graduated pipets, computer, and a watch glass. Pentaaminechloridocobalt (III)
Ammonium chloride was dissolved in ammonia with powdered cobalt (II) chloride hexahydrate. Hydrogen peroxide was then added, mixed, and hydrochloric acid was added. Heat the solution and then let remaining products cool. Filter the products with a Buchner funnel and let the solid dry completely. Spectophotometric Analysis
A sodium thiosulfate stock solution was made that was approximately 0.1 M and used to titrate...
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