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Topic: kinetics study  (Read 4841 times)

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rob

  • Guest
kinetics study
« on: April 01, 2006, 06:42:12 AM »
I have done in the lab a spectrophotometric study fo the kinetics of the iodination of aniline.
Equal initial concetrations of aniline and iodine were used so when I build the rate graphs of 1/A (absorbance of aniline at 500nm) against time, according to the Beer Lambert Law I get straight lines. But I went through the same procedure twice duirng the experiment that is measured the absorbance of aniline samples periodically and build two graphs which are somewhat the same but still the values have some slight differences between them. Thus the two rate constants that I got from the graph slope have a small difference.

>>>please can you help me to comment on the difference between the two kinetic graphs and constants that is any idea as to where might the causes and sources of error lie.

oh, and another question, the aniline I used was freshly distilled and was told that this was important to obtain good results. Please can anybody explain me why, I mean how would it affect my result if it was not freshly distilled?

Please help me if possible. Thank you  ??? ???
« Last Edit: April 01, 2006, 07:46:25 PM by rob »

SoFTiCE

  • Guest
Re:kinetics study
« Reply #1 on: April 01, 2006, 08:40:12 AM »
I think that it happens becouse of:
1) temperatures, concentrations,can be different.
2)maybe, it connected with other factors?
You shoul make near 5 studies, than plot graphs.
Which constants you are have????

SoFTiCE

  • Guest
Re:kinetics study
« Reply #2 on: April 01, 2006, 08:44:15 AM »
Which concentrations you have??? Is they equmolar? Is this is reaction have second rate?
If yes, than 1/A, if rate is 1 than ln(1/A)

rob

  • Guest
Re:kinetics study
« Reply #3 on: April 01, 2006, 08:48:26 AM »
I think that it happens becouse of:
1) temperatures, concentrations,can be different.
2)maybe, it connected with other factors?
You shoul make near 5 studies, than plot graphs.
Which constants you are have????

hey thanks for answering, I think I should explain it better. The  reaction is second order !  The concentration used and temperature and all are the same so I repeated the same thing in the same conditions but noramally the results can never be identical as it is an experiment and because of this the constants differ slightly: 2.3487 and 2.3130. Now I should find out where might the causes and sources of error lie.
For plotting the graphs I took measurements every 10 minutes for 60 minutes (in both cases)
Also dont know why freshly distilled aniline was needed that is what difference would it make in my results if not so.
Please can you give me some help with this??
« Last Edit: April 01, 2006, 08:50:26 AM by rob »

SoFTiCE

  • Guest
Re:kinetics study
« Reply #4 on: April 01, 2006, 09:47:54 AM »
This constants are good, because accuracy of spectrophotometric is near by 1-3%.
You should  took measurements every 2-3 minutes (25-30 minutes) and than every 10 minutes.

Reaction have 2 order by aniline or 2 is order of reaction?

If order by reagents, than k=1/(Ca-Cb)*ln(Cb(?a-C)/(Ca*(Cb-C))
C~A, Ca-concentration of Aniline,

rob

  • Guest
Re:kinetics study
« Reply #5 on: April 01, 2006, 10:35:23 AM »

Reaction have 2 order by aniline or 2 is order of reaction?

If order by reagents, than k=1/(Ca-Cb)*ln(Cb(?a-C)/(Ca*(Cb-C))
C~A, Ca-concentration of Aniline,
Quote

2 is the order of the reaction, aniline is 1, but I'm not trying to work out the constant because I have it that is what I posted here, I simply want to account for the reasons WHY this constants are slightly different, what are the causes and sources of error for this

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