Kinetics of Aquation of Pentaamminechlorocobalt(III) and Kinetics of Decomposition of Tetraamminecarbonatocobalt(III) Revisited. Synthesis, characterization, and determination of pKaof coordinated water in aquopentaamminecobalt(III) trichloride

Material Information

Title:
Kinetics of Aquation of Pentaamminechlorocobalt(III) and Kinetics of Decomposition of Tetraamminecarbonatocobalt(III) Revisited. Synthesis, characterization, and determination of pKaof coordinated water in aquopentaamminecobalt(III) trichloride
Series Title:
Student Symposium 2015
Creator:
Schneider, Sarah ( Author, Primary )
Ghosh, Phalguni ( Advisor )
Middlesex College, Department of Natural Sciences ( Sponsor )
Place of Publication:
Edison, NJ
Publisher:
Middlesex College
Publication Date:

Subjects

Subjects / Keywords:
College students -- poster presentations ( lcsh )
Student Works -- Natural Sciences -- poster presentations ( lcsh )
Chemistry ( lcsh )
Student works -- Natural Sciences -- academic theses ( lcsh )
Middlesex College (Edison, NJ) -- Student works
Middlesex County College (Edison, NJ) ( lcsh )
Temporal Coverage:
Academic Year 2015-2016 ( 2015 - 2016 )
Spatial Coverage:
New Jersey -- Edison

Notes

Abstract:
The hydrolysis of [Co(NH3)5Cl]2+in acidic solution follows a pseudo-first-order rate law , 𝑟𝑎𝑡𝑒=𝑘′[𝐴]𝑚, in which k’=k[H2O]nand A = [Co(NH3)5Cl]2+. The order m was found by the method of initial rates to be ~1. The observed rate constant found at 25°C, 4.17×10-5s-1, was able to be compared to the literature value7of 1.72×10-6s-1. This inconsistency is attributed to differences in ionic strength. The activation energy, Ea, was found to be 45 kJ/mol and the frequency factor, A, was found to be 3.8×103s-1. An enthalpy, ΔH, of 94 kJ/mol matched appropriately with the accepted value of 93 kJ/mol. Additionally, the pKaof coordinated water in [Co(NH3)5(H2O)]Cl3could be determined using titration and spectroscopy. The titrimetric method yielded a pKaof 5.66, while the two spectroscopic methods gave pKa’s of 5.96 and 5.77. An average pKaof 5.80 was determined, making the coordinated water ~10 billion times more acidic than uncoordinated water. Lastly, the kinetics of the decomposition of [Co(NH3)4(CO3)]NO3were studied.The reaction follows a rate law 𝑟𝑎𝑡𝑒=𝑘′[(𝑁𝐻3)4𝐶𝑜𝐶𝑂3+]𝑚, wherek’ = [H+]nat a constant pH. The reaction was studied at three different pH’s and the k’ value determined for each. It was concluded that both m and n equal one, giving the reaction a second order rate law.

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Source Institution:
Middlesex County College Institution
Holding Location:
Middlesex County College Institution
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