Coordination Complex Lab

Melissa Benning
Introduction
The purpose of the coordination complex lab is to determine the absorbance spectra of complexes based on their color. Every complex has its own color which results from the wavelengths of white light it reflects. The complexes will be compared by the color each reflects and by the energy of the waves each absorbs. The purity of the synthesized complex will also be found.
Procedure
Part I: Preparation of the Complex A sample of copper sulfate pentahydrate (6.285g) was weighed out. The copper sulfate pentahydrate was dissolved in water (11.99mL) in a 250mL beaker. The solution was heated on a hot plate to 90 degrees Celsius. A sample of potassium oxalate monohydrate (10.006g) was dissolved in water (50.0mL).
The heated copper sulfate solution was added to the potassium oxalate solution and rapidly stirred. A blue substance formed in the mixture. The mixture was cooled in an ice bath for 20 minutes. The blue crystals were collected by vacuum filtration and were washed once with cold water (12mL), once with 95% ethanol (10mL), and once with acetone (10mL). The crystals were allowed to dry before weighing the product.
Part II: Absorption Spectrum A sample of the complex (0.256g) was weighed out and dissolved in deionized water (9.99mL).
Some of the solution was removed and more deionized water (1.50mL) was added to the solution. A cuvette was filled with deionized water and another with the solution. Each cuvette was filled to the same level. The transmittance of the solution was found at 400nm and then consecutively recorded at intervals of 25nm. Absorbance was calculated from percent transmittance and then plotted on a graph as a function of
wavelength.
Part III: Analysis of the Complex A buret was filled with a potassium permanganate solution (0.02015M). Two samples of the complex were weighed out (0.157g and 0.155g). A solution of sulfuric acid (1.0M) was added to each sample of complex (12.5mL and 12.6mL respectively). The solution of complex and sulfuric acid was heated on a hot plate to 90 degrees Celsius. The potassium permanganate was slowly added. Two titrations were done one with each mass of complex. The meniscus of the permanganate was difficult to read because of the deep, purple color. The volume was measured from the top of the solution. A faint red appeared as the permanganate was titrated in the light blue solution of complex and sulfuric acid. The complex solution became clear at the end of the titration. The average volume of the of the titrated permanganate solution (15.3mL) was used to find the concentration of oxalate and then percent purity.
Observations and Data
Data Table 1-Preparation of the Complex
|Material |Mass/Volume |Appearance |
|copper sulfate (hydrate) |6.285g |solid, blue crystal shape |
|Water |11.99mL |----- |
|potassium oxalate monohydrate |10.006g |transparent liquid |
|Water |50.0mL |----- |
|cold deionized water |12mL |----- |
|95% ethanol |10mL |transparent liquid |
|Acetone |10mL |transparent liquid |
|Complex |9.198g |blue powdery substance |

Data Table 2-Absorption Spectrum
K2[Cu(C2O4)2]•2H2O
|Wavelength (nm) |400 |425 |450 |
|Complex |0.157g |.155g |.156 |
|H2SO4 |1.0M |1.0M |----- |
|H2SO4 |12.5mL |12.6mL |12.6mL |
|KMnO4 |.02015M |.02015M |----- |
|KMnO4-initial |12.0mL |27.0mL |----- |
|KMnO4-final |27.0mL |42.6mL |----- |
|KMnO4-total |15.0mL |15.6ml |15.3mL |

Conclusions and Questions The maximum absorption of K2[Cu(C2O4)2]•2H2O was found. The absorption curve was valid. The objective was met. The absorptions of each complex were compared . The K2[Cu(C2O4)2]•2H2O complex absorbed the most light at wavelengths of 625-675nm. The complex reflected light with wavelengths of 450-575nm. The color of the substance was blue which correlates with the absorption curve. 1)The limiting reagent was the copper sulfate pentahydrate (.0252mol). 2) The percentage yield of the product was 103%. The error resulted from water that was not completely filtrated from the complex before weighing in Part I. 3) The absorption maximum was 650nm. The wavelengths with the highest absorption were red, orange, and some violet. The lowest absorptions on the curve, the colors that were reflected, were at the wavelengths of blue, green, and yellow. The color of the complex was blue. 4) The [Cu(NH3)4]SO4•H2O complex was dark blue and the maximum absorption was at 600nm. This complex reflected orange. 5)The percent purity of the compound was 87.2%. The percent purity could be higher due to experimental errors.