The objective of this lab is to determine the formula of an unknown Co (III) complex through determination of outer sphere chloride content and hence total chloride content in the complex. Co (III) tends to form numerous coordination complexes, of which the most common ones are those with ammine ligands. The unknown Co(III) complex will have a general formula of [Co(NH3)(6-x)Clx]Cl(3-x) where x is an integer that could have values of 0, 1, 2, or 3.1 The coordination number of Co(III) is 6 so a total of 6 ligands can bind to it. The unknown complex given is a solid and bears two different types of chloride ions—inner sphere chloride ions and outer sphere chloride ions. The inner sphere chloride ions act as ligands while the outer sphere chloride ions act as counter-ions to balance the positive charge of the unknown Co (III) complex. The experimental techniques employed to determine the outer sphere and total chloride content are ion exchange chromatography and Fajan's method of chloride ion titration respectively.
[...] The experimental outer sphere chloride content is calculated to be an average of 8.033 E-3 moles/g, with an average percentage error of The experimental inner sphere chloride content is 5.839 E-3 moles/g, and the experimental total chloride content is 1.387 E-2 moles/g, with an average percentage error of Both percent errors are relatively low. In particular, the outer sphere analysis is very accurate. Despite the fact that the total chloride ion concentration experiment shows greater error, the data is still fairly accurate and precise since both trials generally agreed with each other. [...]
[...] The heating and lack of separation of the inner sphere ions were the primary source of error, but the experimental results still were correct and both accurate and precise. Conclusion: The purpose of the lab was accomplished. The unknown cobalt complex was determined to be [Co (NH3)5Cl] Cl2. The total chloride ion, inner sphere chloride ion, and outer sphere chloride ion contents were all determined through ion-exchange chromatography and Fajan's method. The outer sphere chloride ion concentration is 8.033 E-3 moles/g, the inner sphere chloride concentration is 5.839 E-3 moles/g, and the [...]
[...] Total Chloride Analysis: Sample Chloride content (moles) 1 E-3 2 E-3 Table Total Chloride Content. The average chloride content is 2.401 E-3 moles. Calculation of Sample Outer Inner Total (mol/g) Approximate Sphere Sphere Ratio of Inner (mol/g) (mol/g) to Outer Table Calculated Values for Moles Cl- per gram of Co (III) complex Given the general formula of the unknown complex [Co (NH3) Clx] Cl , and the above ratios presenting that x = the formula of the unknown complex is [Co (NH3)5Cl] Cl2. [...]
[...] Total (Outer and Inner) Sphere Chloride Analysis Another two samples of the unknown Co (III) complex were weighed out ( 0.1724 g and 0.1750 and placed in separate 100mL beakers. As in the previous part, the same procedure was repeated separately for each sample. The samples were each added to 30mL of distilled water and 5mL of 1M NH3 and heated to 60 ºC on a hotplate. As heated, the solution turned from purple to a dark reddish-black. Once the purple disappeared, the solution was taken off the heat and 8 mL of 1M HNO3 was added and the solution turned clear. [...]
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