In this experiment, the substance was tested at on temperature (85 degree Celsius), the rate constant for the substance at 60 degrees Celsius was given, and the remaining temperatures (the other 5) were obtained from a posting of other group’s calculations. For the preparation of the compound pentaamminechlorocobalt(III)chloride, compounds [Co(NH3)4CO3]NO3, HCl concentrate, and NH3 concentrate are experimentally combined. The first reason that this experiment is useful is because the compound would in future weeks, be used for following experiments to determine both rate constant and activation energy of pentaamminechlorocobalt(III)chloride.
Other reasons to study synthesis and kinetics using hydrolysis would help to determine the behavior of the reaction as being independent or dependent of a base-catalyst 1. Also, by understanding the kinetics of this compound, other, more complex compounds, can be easier to understand. Learning and understanding behaviors of the hydrolysis can help to make better predictions when like compounds react in other similar mixings of compounds 4. Kinetics is the study of motion.
In the study of kinetics of the compound being prepared, the H+ ion movement can be determined 3.
Having a model of this reaction can be useful in predicting reaction kinetics for similar reactions. Experimental (Experiment 1 Handout, PLU Department of Chemistry) In this experiment, pure ethanol was used. Also the HCl and NH3 was a concentrate. First, 5. 0 grams of [Co(NH3)4CO3]NO3 was dissolved in 50 mL of H2O in a beaker. When the 5 to 10 mL of HCl was added to the previous solution, the CO2 was expelled and HCl was added until all of the CO2 was expelled.
When the NH3 was added (about 5mL) the solution was being neutralized until the pH paper read that neutralization was obtained.
The solution was heated for 20 minutes at a temperature just below boiling point. Heating the solution was required in order to start the process of crystallization so that a solid could be obtained. The solution was then slightly cooled and 75 mL of HCl was added. At this point, the solution turned a purple color with a hint of red the instant the HCl was added. Hydrolysis was the method being used. The solution was then reheated for about 45 minutes. The solution had to be heated for this long period of time for the best crystallization results.
The solution was then cooled again so that the crystallization would begin. After purplish-red crystals had formed along the bottom of the beaker, the compound was washed using decant with ice-cold water. This would preserve the solid crystals before vacuum filtration. After that, the compound was placed on a filter for vacuum filtration. While filtering, the compound was rinsed with 2 to 3 mL of ethanol repeatedly. Vacuum filtration was run for about 5 minutes. The substance was then set in an oven at 120 degrees Fahrenheit to dry and let the moisture out for accurate weighing. Results and Discussion
A rate constant was found using an 85 degree Celsius temperature. The rate constant was determined to be 1. 9 x 10-2 min-1. This was found by using Beer’s law A=? bc. Where A=absorbance, ? =the molar absorptivity, 21 cm, b=the path length, 1 cm, and c=the molar concentration of the sample, 1. 2 x 10-2M.. When the absorbance values were corrected using an infinite time equation (based on Beer’s law), our A(inf)=. 250. The reaction was first order. A plot of ln(A-A(inf)) gave somewhat of a straight line. This linear plot however showed the several errors that turned up in the lab.
Results were extremely inconsistent. Errors in this part of lab were all due to the experimental. Also, the calibration of the colorimeter could have been slightly incorrect. Another possible error was in the constancy of the heating because the flasks were being taken in and out of the water. Even though the water bath was reading at 85 degrees Celsius, the solution inside the flask may have not consistently been held at that temperature. In a similar lab in the synthesis of Pentacoordinate Glyoxime-based Ligand and Preparation of Its Chlorocobatl(III) Complex a similar compound is being synthesized.
The synthesis of a perfect structure of this complexity is hard to obtain because of the “brutal conditions required” 2. In the Kinetics of Reduction of Co(NH3)5Cl2+ experiment, rate constant values produce better fitting graphs of the exact same patter that the lab performed was supposed to. In this lab Co (NH3)5Cl2+ is being reacted with Ti(III) at 25. 2 degrees Celsius using 1. 0M Ionic Strength. This closely relates. The reaction is also first order. The rate law is given by: rate=k2 [Co (NH3) 5Cl2+][reactant] 3. Other temperature’s rate constants were collected in order to calculate an average rate constant.
Outliers were meant to be eliminated but it was hard to tell which data was significant and which was not. The data was as follows: Degrees Celsius (top row), min^(-1) (bottom 4 rows) It is unclear whether the constant rates are supposed to be negative or positive and data is extremely inconsistent and hardly fits any trend line at all.
Theoretically, by measuring the rate of reaction at various temperatures, the energy of activation should be found. Also, theoretically, graphs such as log k versus 1/T should produce a straight line trend and the slope of that line would determine the activation energy.
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