An Investigation Of The Order Of The Reaction Of Iodine With Propanone

[Jessieee]

we've done an experiment

iodine reacts with propanone

the reaction mixture contains

-50 cm3 of 0.02 M I2 in aqueous KI solution

-25 cm3 of H2SO4

-6.25cm3 of propanone

-18.75am3 of distilled H2O

 

while other groups used different volume of propanone and water but the total volume of reaction mixture is still 100cm3

 

and after mixing...

After 5 minutes, pipette 10.00 cm3 of the reaction mixture into another conical flask containing 10 cm3 of the sodium hydrogencarbonate solution (measure this during the 5 minutes interval) noting the time at which this is done. Mix the solution thoroughly and then titrate with the diluted sodium thiosulphate solution using starch as indicator.

After 10, 15, 20, 25 and 30 minutes withdraw 10.00 cm3 portions of the reaction mixture from the flask and carry out the above procedure each time.

 

results...

Time 5 10 15 20 25 30 35 40 45

 

Vol. 7.00 6.80 6.80 6.60 6.40 6.40 6.30 6.30 6.20

 

 

so a graph which vol of thiosulphate used against time was plotted...

 

need to ans some questions..

1. how can the rate of the reachtion be determined from the graph?!

2. did the iodine concentration change at a uniform rate throut the experiment?! (from my graph, i got "yes" as i seems like got a st.line graph)

3. is the rate of change of the iodine concentration dependent on the iodine concentration? (again, seems that it should be dependent, but from my graph, it's independent..lol, my graph isn't a curve, is it becoz the conc of propanone used is too low?!)

4. what is the order of the reaction with respect to iodine? (how can i get the ans!?)

5. does iodine take part in the rate determining step of this reaction? (how do i know?! i guess yes, but seems no evidence?!)

6. what is the significance of the intercept of the graph? (no idea..)

7. what must be the conc of the sodium thiosulphate solytion have been!? (how to calculate? do i know the conc of iodine??)

 

sorri for soooooo many questions. stupid me.. >.<!

[sheepy]

Hi, i'm doing this coursework.

Just wondering how you got on.... you posted this in 2005 lol

[Kaeroll]

Since it's already been bumped without an answer I feel it's worth providing some advice. Apologies if anyone feels this is necromancy, heh.

 

1. What is a rate? It is how fast a quantity changes with time. You can get this from a straight-line graph as a gradient.

 

2. The OP answered their own question here.

 

3. Also answered. If the rate were dependant upon , the rate would vary with (I realise that's stating the obvious...). As it doesn't, the rate must be independant of .

 

4. To eyeball it, if the rate of reaction is independant of a reaction, it can have only one possible order. Think about it. A more thorough way to investigate this is to repeat the experiment with varying initial , holding all else constant, and see what effect it has on rate.

 

5. Once the answer to #4 is found, this will become evident. If the rate is not influenced by , is it involved in the aptly-named rate-determining step?

 

6. Where is the intercept found? (t=0). What should equal at this point? (It's a known quantity calculated from the protocol)

 

7. There's probably several ways to work this out. Personally I'd extrapolate back to initial to determine what volume would be required. As initial is known, the extrapolated volume can be used to determine [thiosulphate].

 

For bonus points, consider what the rate-determining step of the reaction might be. Spoiler: the OP was right, is not involved in the RDS. To work this out try to draw out a mechanism for the reaction. Three steps are required.

 

I plotted the OP's data in Excel and wasn't too impressed- the data does seem to curve somewhat but this is likely down to error more than anything else. More points would probably have been nice.

 

(for some reason in this post, is coming out in lower case. Anyone know why?)

 

Kaeroll