to investigate the order or reaction of iodine with propanone

[k_ling]

hi there i'm doing a lab report about investigation of the order of the reaction of iodine wif propanone

and i find it a bit difficult so i'd like to ask a few questions , hope somebody could help, thz

 

1.) How does the starch indicator function?why is it added near the end point?

(can i just write starch turns blue when meetin iodine? and i really dun noe y it must be added near the end pt==" )

2.)the tutor requests us to outline another method to follow the kinetics of the reaction. what method??

 

3.)and wt means by " mechanism of the reaction"?

 

please help!!!!!!!!!!!!thz a lot><

[mississippichem]

hi there i'm doing a lab report about investigation of the order of the reaction of iodine wif propanone

and i find it a bit difficult so i'd like to ask a few questions , hope somebody could help, thz

 

1.) How does the starch indicator function?why is it added near the end point?

(can i just write starch turns blue when meetin iodine? and i really dun noe y it must be added near the end pt==" )

2.)the tutor requests us to outline another method to follow the kinetics of the reaction. what method??

 

3.)and wt means by " mechanism of the reaction"?

 

please help!!!!!!!!!!!!thz a lot><

 

Well, the mechanism of the reaction are the steps that both molecules must take in order to react with each other making a transition state and possibly an intermediate that will eventually degrade to the products. What method are you currently using to investigate the order of reaction? Are you using the doubling of concentrations method? With this method, concentrations of various reactants are varied by a known stoichiometric amount, the quantitative effect on the rate is observed.

 

Another method is to plot concentration versus time and find the shape of the resultant line. Zero order reactions give a linear plot with slope of [imath]-k,[/imath]. First order reactions give a linear plot when time vs. [imath]log[conc.][/imath] is plotted with a slope of[imath] -k[/imath]. Second order reactions give a linear plot with a slope of [imath] k [/imath] when time vs.[imath]\frac{1}{[conc.]}[/imath] is plotted.

 

As far as adding the indicator at the last step. I don't know why because I don't know enough about your procedure, please explain further.

Edited February 20, 2011 by mississippichem

[k_ling]

oh can u explain the 1st method more detailedly? maybe state the procedures plz?

the 2nd method is uesd and the starch indicator was added into the aliquot(CH3COCH2I + I-) when titrating with sodium thiosulphate.

 

 

thank you so much

Edited February 20, 2011 by k_ling

[mississippichem]

oh can u explain the 1st method more detailedly? maybe state the procedures plz?

the 2nd method is uesd and the starch indicator was added into the aliquot(CH3COCH2I + I-) when titrating with sodium thiosulphate.

 

 

thank you so much

 

You vary the concentration of reactants while holding the other reactant concentrations constant. If you double the concentration of a reactant and there is no change in observed rate, then the reaction is zero order with respect to that reactant giving an [math] [X]^{0} [/math] term in your rate equation of the form:

 

[math] r=k[X]^{n}[Y]^{m}[Z]^{l} [/math]

 

If doubling that concentration doubles the rate, then the reaction is first order with respect to that reactant. If the rate increases by a factor of 4; then second order. You could also compare your results against those predicted by the order specific integrated rate laws derived as follows from a differential rate law:

 

[math]-\frac{d[X]}{dt}=-k_{1}[X][/math]

 

[math]\frac{d[X]}{[X]}=-k_{1} dt[/math]

 

[math]\int\frac{d[X]}{[X]}=\int-k_{1} dt[/math]

 

[math]ln[X]=-k_{1}t+r_{0}[/math]

 

*where r_0 is the instantaneous initial rate

 

This is the derivation for a first order process but the others are similar. You can always find these rate laws already integrated for you though. I just enjoy the process.

Edited February 21, 2011 by mississippichem