Propanone And Iodine Coursework Meaning

 

Chemistry Individual Investigation Yann Perusset 13F

2

To increase the number of particles with enough energy for a successful collision the temperature canbe increased. This concept is again shown in the distribution curve shown above, withT1being thecolder temperature andT2being the warmer. The area under the curve past the E

A

shows thenumber of particles with enough energy to form a successful collision. Basically, reactions go faster athigher temperatures because a larger proportion of the colliding molecules have the minimumactivation enthalpy needed to react.Many factors can affect the overall rate of a reaction, the main factors being concentration,temperature, particle size and the presence of a catalyst. When I come to working out the rateequation and I increase the concentration of one of the reactants it is important to keep all otherfactors the same to determine what effect that particular solution has on the rate without any outsideinfluences. An increase in the concentration of a solution increases the amount of particles within it,the more particles there is, the more likely a successful collision.

Order of reaction, rate constants and rate equations

2+3

Rate Equations and rate constant

With a rate equation, it is possible to see how the concentration of each of the reactant affects therate of a reaction. An example of a simple rate equation is shown below.

Rate=k[A]

x

[B]

y

The total order of a reaction is the sum of the orders of the individual reactants. So for this reaction itwould be the sum of x and y.From the rate equation it is also possible to find out the rate-determining step. From looking at theorder of each of the substances it will tell you the relative number of moles of each substanceinvolved in the rate determining step. For example, assume substance A in the equation above is firstorder, this means that there will be one substance in the rate-determining step. From this, it wouldthen be possible to create a mechanism for the reaction.The rate constant can be calculated by rearranging the rate equation. Below is an example of the rateequation above but rearranged in terms of the rate constant, k:

=







To obtain a reliable value for the rate the initial rates method would be used (shown below)Once the rate equation is worked out, it can be easily linked to the reaction mechanism by looking atthe rate determining step.

Colourimetery

4

The rate of a reaction is the change in concentration of a reactant or product divided by the timetaken for the change to occur. Therefore to calculate the rate, you have to be able to measure theconcentration of a solution. To do so I shall use the process of Colourimetery. A colorimeter can beused to measure the change in colour of a reaction. It works on the principle that coloured solutions(like iodine that I will be using) absorb certain wavelengths of light. The amount of light that isabsorbed by the solution is known as the absorbance of the solution.The absorbance is proportional to the concentration of the solution used (Abs Conc)Known concentrations of the coloured solution are used to produce a calibration curve which canthen be used to find the concentration of any absorbance value that has that coloured solution withinit.

 

Kinetics of the reaction between propanone and Iodine in acid solution

2

Section 1

Equation for the reaction:

I

2(aq)

+ CH

3

COCH

3(aq)

→ CH

3

COCH

2

I

(aq)

+ H

+(aq)

+ I

¯(aq)

Iodine + Propanone

Iodopropanone + Hydrogen (cation) + Iodide (anion)

Introduction: Chemistry of the reaction:

Propanone and Iodine react together in an irreversible redox reaction to form Iodopropanone.This reaction is catalysed by aqueous Hydrogen ions (protons) produced from the Sulphuricacid. As the reaction proceeds the dark brown colour of Iodine in solution gradually turnscolourless. This is due to the concentration of Iodine in solution decreasing as it is being usedup reacting to produce colourless Iodide ions and the Iodopropanone. I have chosen to monitorthe progress of this reaction by measuring the absorbance value of this colour change in adigital Colourimeter.

Aims:

1). I aim to individually vary the concentrations of 

each

reactant (Iodine and Propanone)including the acid catalyst (Sulphuric acid) in solution and measure its effect on the rate of reaction in Absorbance (Beer-Lambert Law) using Colourimetry. All of data collected will beused to construct line graphs for each concentration of reactant investigated per experiment.Using the trends of these line graphs, the initial rates of reaction method can be used bydrawing tangents from the starting plots of the reaction progress curve to calculate each rateof reaction

(A

/s

-1

 ).

Finally these values of rate of reaction can be plotted against concentrationof the reactant being investigated to deduce the order of reaction with respect to that reactant- this process will be carried out for each reactant.2). Using the orders of reaction and the rate equation, I aim to calculate a mean rate constant(at room temperature). Through addition of reactant orders (

m+n)

the overall order of reactioncan be deduced.Independent Variable(s):-

Concentration of Iodine (in situ)

(mol dm

-3

)

-

Concentration of Propanone

(mol dm

-3

)

-

Concentration of Sulphuric acid

(mol dm

-3

)

Dependent Variable

 –

Absorbance

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