Chemistry Experiment On Temperature: a Report

Abstract

In this experiment, the synthesis of pentaamminechlorocobalt(III)chloride was conducted, and its kinetics were studied. The rate constant at 85 degrees Celsius was determined to be 1.9 x 10^-2 min^-1. The reaction was found to be first order. However, the experiment encountered several sources of error, leading to inconsistent results. This report discusses the experimental procedure, results, and potential sources of error, along with recommendations for improving the experiment's reliability.

Introduction

The objective of this experiment was to synthesize pentaamminechlorocobalt(III)chloride and study its kinetics.

This compound has practical applications in future experiments to determine its rate constant and activation energy. Additionally, understanding the hydrolysis kinetics of this compound can provide insights into the behavior of reactions with base-catalysts.

Studying the kinetics of this compound also contributes to a broader understanding of chemical reactions. Kinetics is the study of reaction rates and mechanisms, and it plays a crucial role in predicting and controlling chemical reactions. By having a model reaction like pentaamminechlorocobalt(III)chloride, it becomes easier to predict reaction kinetics for similar compounds and reactions.

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Materials and Methods

The following materials were used in the experiment:

• [Co(NH3)4CO3]NO3
• HCl concentrate
• NH3 concentrate
• Pure ethanol
• H2O

The experimental procedure was as follows:

1. Dissolve 5.0 grams of [Co(NH3)4CO3]NO3 in 50 mL of H2O in a beaker.
2. Add 5 to 10 mL of HCl to the solution to expel CO2 and continue adding HCl until all CO2 is expelled.
3. Neutralize the solution by adding approximately 5 mL of NH3 until the pH is neutral.
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4. Heat the solution for 20 minutes just below its boiling point to initiate crystallization.
5. Cool the solution slightly and add 75 mL of HCl, resulting in a color change to purple with a hint of red.
6. Continue heating the solution for approximately 45 minutes to ensure proper crystallization.
7. Cool the solution again to promote crystallization.
8. Perform a decantation to separate solid crystals.
9. Rinse the solid with ice-cold water.
10. Perform vacuum filtration on the compound.
11. Rinse the compound with 2 to 3 mL of ethanol during filtration.
12. Dry the substance in an oven at 120 degrees Fahrenheit for accurate weighing.

Experimental Procedure

Once the compound was synthesized, the kinetics of the reaction were studied at various temperatures. The rate constant at 85 degrees Celsius was found to be 1.9 x 10^-2 min^-1 using Beer's law, which relates absorbance (A) to molar absorptivity (ε), path length (b), and molar concentration (c) as A = εbc. The absorbance values were corrected using an infinite time equation based on Beer's law, resulting in A(inf) = 0.250.

The reaction was determined to be first order, and a plot of ln(A - A(inf)) against time gave a somewhat linear relationship, although it revealed several experimental errors. The source of inconsistencies could be attributed to experimental factors, including variations in heating, calibration of the colorimeter, and human error during data collection.

Results

The rate constant at 85 degrees Celsius was determined to be 1.9 x 10^-2 min^-1. However, the data obtained from other temperatures showed significant inconsistencies and did not fit any discernible trend. Theoretical expectations were that measuring the rate of reaction at various temperatures would allow the calculation of the activation energy, and graphs like log k versus 1/T should produce a straight line, with the slope determining the activation energy.

Unfortunately, the data collected did not conform to these expectations, and further analysis is required to understand the observed discrepancies.

Discussion

The experiment aimed to synthesize pentaamminechlorocobalt(III)chloride and study its kinetics, particularly the rate constant at different temperatures. While the rate constant at 85 degrees Celsius was successfully determined, the results from other temperatures exhibited inconsistencies that require careful consideration.

The experiment encountered several potential sources of error. Variations in heating could have affected the reaction rate, as the solution inside the flask may not have consistently reached and maintained the desired temperature despite the water bath reading at 85 degrees Celsius. Calibration issues with the colorimeter may have contributed to inaccuracies in absorbance measurements. Additionally, human error during data collection could have introduced further inconsistencies.

It is important to note that the synthesis of pentaamminechlorocobalt(III)chloride is a challenging process, as mentioned in the synthesis of Pentacoordinate Glyoxime-based Ligand and Preparation of Its Chlorocobalt(III) Complex experiment. The harsh conditions required for its formation can result in variations in the final product. These challenges may have influenced the reaction kinetics observed in this experiment.

The inconsistency in the collected data makes it difficult to draw definitive conclusions about the activation energy of the reaction. Further experiments and data analysis are needed to obtain a clearer understanding of the kinetics of this reaction.

Conclusion

In conclusion, this experiment aimed to synthesize pentaamminechlorocobalt(III)chloride and study its kinetics. While the rate constant at 85 degrees Celsius was successfully determined, the results from other temperatures were inconsistent and did not conform to theoretical expectations.

Potential sources of error, including variations in heating, colorimeter calibration, and human error, may have contributed to the observed discrepancies. Additionally, the challenging nature of the synthesis process for pentaamminechlorocobalt(III)chloride can result in variations in the final product, which could affect reaction kinetics.

Further experiments and data analysis are necessary to better understand the kinetics of this reaction and to determine the activation energy. Improvements in experimental techniques and data collection may help reduce inconsistencies and provide more reliable results in future studies.

Recommendations

Based on the challenges and inconsistencies encountered in this experiment, the following recommendations are made for future studies:

1. Ensure precise and consistent temperature control during the reaction to minimize variations in heating.
2. Thoroughly calibrate the colorimeter to improve the accuracy of absorbance measurements.
3. Implement rigorous data collection procedures to minimize human error.
4. Consider conducting multiple trials to obtain more reliable and consistent data.
5. Explore alternative methods for synthesizing pentaamminechlorocobalt(III)chloride that may yield more consistent results.

By addressing these recommendations, future experiments can strive for more accurate and reliable results in the study of pentaamminechlorocobalt(III)chloride kinetics.

References

•  Jackson, G. W. , Dickie, A. J. , McKeon, J. A. , Synthesis, Structure, and Kinetics and Stereochemistry of Base-Catalyzed Hydrolysis of meso-and rac-[Co2(tmpdtne)Cl2]4+, Bis(pentaamine) Complexes Devoid of Deprotonatable NH Centers;
• Inorganic Chemistry, Vol. 33, No. 2, 2005, pp. 401-409. 2 Sharpless, K. B. , Jensen, H.P. ,Synthesis of Novel Pentacoordinate Glyoxime-Based Ligand and Preparation of Its Chlorocobalt(III) Complex;
• Inorganic Chemistry, Vol. 13, No. 11, 1974, pp. 2617-2620. 3 Orhanovic, M. , Earley, J. E. , Kinetics of Reduction of Co(NH3)5Cl2+ and cis-and trans-Co(en)2Cl2+ by Ti(III);
• Inorganic Chemistry, Vol. 14, No. 7, 1975, pp. 1478-1481. 4 Dickie, A. J. , Hockless, D. C. R. , Willis, A. C. , McKeon, J. A. , Jackson, W. G. , A Unique Mechanism for Base Catalyzed Hydrolysis of Pentaaminecobalt(III) Complexes Containing Picolyl Residues;
• Inorganic Chemistry, Vol. 42, No. 12, 2003, pp. 3822-3834.