Preparation of a Coordination Complex of Copper (II), Lab Report Example

Introduction

The purpose of this lab is to characterize a coordination complex of copper (II) (Worksheet). The purpose of this analysis is to gain a greater understanding of the elements and molecules that copper can form complexes with. In the human body, such complexes are responsible for the maintenance of homeostasis (Ma). This experiment is based on the Lewis acid/base theory because the metal ion behaves as a Lewis acid and ligand molecules behave as Lewis bases. A coordination compound is defined as a complex with a metal atom in the center with a fixed number of molecules or ions surrounding it that are bonded to it covalently, forming a fixed shape (Purdue).

Materials and Procedures

Approximately 1 gram of copper(II) sulfate pentahydrate was weighed out and dissolved in 10 mL of water. The color of the solution was then recorded. 5 mL of concentrated ammonia solution was then added to the mixture. After all of the ammonia was dissolved, the color of the solution was recorded. 10 mL of ethyl alcohol was then added to decrease the solubility of the tetramminecopper(II) complex. The solid precipitate was allowed to stand for 5 minutes and then filtered under suction. While filtering, the precipitate was washed with ethyl alcohol, stirred, and dried.

After the precipitate was completely dry, the percent yield of tetramminecopper(II) sulfate monohydrate was calculated. A small drop of this product was placed in a small amount of water. Concentrated HCl was then added until a color change was observable. A small amount of the copper complex was then heated in a test tube in a burner flame. A piece of moist pH test paper was held by the mouth while it was being heated. The vapor was wafted and observed to detect the presence of ammonia. No changes were made to the procedure either on purpose or accidentally.

Results and Observations

Mass of copper(II) sulfate pentahydrate taken: 0.930 g

Theoretical yield of product: 0.92

Mass of copper complex obtained: 0.31 g

% yield: (actual/expected)*100 = 33.6%

After adding the HCl to the product, the color change occurred after the first drop. After 10 drops, it still remained clear. Therefore, it is likely that HCl replaced NH₃. When the tetramminecopper(II) sulfate monohydrate was heated, it exhibited a pH change. The paper changed to a light green color, indicating a pH of 8. After sensing the character of the vapor from this reaction, the presence of ammonia gas was confirmed.

In this experiment, there was a potential for human error due to the likelihood that the weight of the reactants and products were not weighed precisely. Furthermore, the results cannot definitively be called valid because the experiment was only performed once.

Conclusion

 The color change experiment showed that the HCl replaced NH₃ in the chemical reaction. The results indicated that ammonia forms when tetramminecopper(II) sulfate monohydrate is heated in addition to changing to having a pH of 8. This helps us understand the strength of the coordination complex; it must be resistant to temperature change and pH change to remain effective in the body (Worthington).

Works Cited

Ma Z, Jacobsen SE, Giedroc. DP. Metal Transporters and Metal Sensors: How Coordination Chemistry Controls Bacterial Metal Homeostasis. 109.10 (2009): 4644–4681.

Purdue. What Is A Coordination Compound? N.D. Web. 22 April 2015. Worksheet.

Worthington. Introduction to Enzymes. N.D. Web. 22 April 2015.