What’s the Order of reaction with respect to Iodide ions in the Iodine clock reaction

My data suggests it’s order 2 with respect to iodide ions, but google suggests it’s order 1. I’ve searched the whole internet and could not find a value for this.

Any help will be much appreciated! Thanks.

Reply 1

username5450504

Original post by TheoP31

It is first order, i also recently did this experiment and from my data it was first order- maybe your results are inaccurate?

Reply 2

TheoP31

Original post by alisha.h

It is first order, i also recently did this experiment and from my data it was first order- maybe your results are inaccurate?

Oh is it really?
Thank you Alisha!

Here are the results from the lesson today:

If I double the volume of KI, my reaction rate quadruples. If I triple the volume, the rate becomes 9 times greater. This indicates that it’s second order for me- seems to work for all of the data values.

I don’t know how it’s first order?

Reply 3

username5450504

Original post by TheoP31

Oh is it really?
Thank you Alisha!

Here are the results from the lesson today:

when finding orders of reactions, you need to look at the conc., not volume, so find the conc. of I in each volume of KI, and then see how the rate changes

Reply 4

TheoP31

Original post by alisha.h

when finding orders of reactions, you need to look at the conc., not volume, so find the conc. of I in each volume of KI, and then see how the rate changes

Ohhh, I thought we was able to use volume to work it out too- since rate is defined as “the change in the amount of product formed or reactant used per unit time”. I suppose if it HAS to be a concentration, then I will convert them! Thank you!

So how would I even convert them to concentrations? For a volume of 5cm³ of KI, would I do...
(5/25) x 0.10 ?
This gives me a concentration of 0.02moldm^-3.

So for a volume of 25cm³ of KI, the concentration would be 0.1moldm^-3 ?

Thanks for your help Alisha!

Reply 5

username5450504

Original post by TheoP31

you're welcome! the way I was told to do was divide the volume of KI by the total overall volume of all reactants (in my case was 10), and then multiply that value by the initial conc. of KI solution. - e.g. volume of 5cm^3 of KI, i did 5/10 X 1.00 mol dm-3 (initial conc. of KI)

However, looking at your table of results it looks like KI was your only solution...? Did you have any other reactants?

Reply 6

TheoP31

Original post by alisha.h

Ohh I see. Thank you for the help!
I emailed my chemistry teacher and she says we don’t need to work out the concentrations. Simply just record 1/t in another column of the table; to work out the order of reaction wrt I- .

And yes we did of course use other reagents- but they are kept constant throughout so it’s not necessary to include in the results table.

Reply 7

username4407536

Original post by TheoP31

If you kept total volume constant, the volume of KI will be proportional to the concentration of KI

The difference between your experimental result and literature values is expected as there will be some degree of experimental error