Kinetics of Chemical Reaction – Iodination of Cyclohexanone Essay

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EXPERIMENT 6

Title  
Kinetics of Chemical Reaction – Iodination of Cyclohexanone

Aim
To determine the value of the rate constant, k and order of reaction, a, b and c, and also to suggest a mechanism which agrees with the rate equation that has been obtained.

Background Theory

The basis of the theory of absorbance is as follows:

Io ―――――→ sample ―――――→I

if Io = I,   no absorbance occur
Io > I, the sample absorbs certain amount of light wave
Io < I, the sample emits certain amount of light of certain wave length.

THE HALOGENATION (IODINATION) OF KETONES (CYCLOHEXANONE)
This experiment examined the rate of iodination of cyclohexanone in an aqueous medium. To increase the amount of iodine in the solution, iodine is converted to a more soluble complex ion, I3- by the addition of excess iodide ion:
I2 + I- →I3-

One of the characteristic reactions of ketones is the substitution of a halogen for one of the hydrogen is adjacent to the ketone group. The net reaction is:

This reaction has been studied extensively and occurs for a wide variety of ketones. In general, the halogenations of a ketone can be represented as follow:

The main evidence for any mechanism is provided by kinetic studies to determine an experimental rate law.
Following the rate law of chemical kinetics, the differential rate equation for the reaction could be written as follow:

Where k = rate constant; a, b,c are the orders of the reaction of S, I3-, and H+ respectively.

I3- ion is the only coloured species in the reaction mixture, a spectrophotometer can is used to measure the change in its concentration, by applying the Beer-Lambert Law

Where A= absorbance, ε= molar absorption coefficient, [I3-]= concentration and /= optical path length, that is, the distance travelled by the light through the solution. The ideal wavelength for the measurement of I3- ion concentration is 565nm.

Deriving from the Beer-Lambert Law equation,

where ε-1 /-1...

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