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# Iodine Clock reaction, determining rate constant k Watch

1. Hi,I've been doing the Iodine-Clock Reaction for my Salters investigation, using Potassium Iodide, Sodium Thiosulphate and persuklfate, I know the order of the reaction is rate=k[I-][S2O82-] , so they're both first order.

But how do I find the rate constant k?

I kept the conc of one substance constant for one experiment, then changed the other and vice versa, I have all the times/rates I just have no clue how to do it.

Thanks,

Ben Ingham
2. (Original post by Ben Ingham)
Hi,I've been doing the Iodine-Clock Reaction for my Salters investigation, using Potassium Iodide, Sodium Thiosulphate and persuklfate, I know the order of the reaction is rate=k[I-][S2O82-] , so they're both first order.

But how do I find the rate constant k?

I kept the conc of one substance constant for one experiment, then changed the other and vice versa, I have all the times/rates I just have no clue how to do it.

Thanks,

Ben Ingham
You have the equation, simply rearrange:

k = rate/[I-][S2082-]

Using the corresponding rates and concentrations.
The answer should be similar no matter which set of results you use, assuming you're performed the procedure correctly.
3. (Original post by Cyclohexane)
You have the equation, simply rearrange:

k = rate/[I-][S2082-]

Using the corresponding rates and concentrations.
The answer should be similar no matter which set of results you use, assuming you're performed the procedure correctly.

The problem I have is that I don't know which values to use for [I-] and [S2O82-, I did two experiments keeping one conc. constant and varying the other, so do I use 1 for the constant value and the concentration of the other to work it out?
4. (Original post by Ben Ingham)
The problem I have is that I don't know which values to use for [I-] and [S2O82-, I did two experiments keeping one conc. constant and varying the other, so do I use 1 for the constant value and the concentration of the other to work it out?
It shouldn't matter, the rate constant should be the same/similar whichever set of results you use.
If you're unsure, calculate the rate constant using a few different sets of data, to see whether they're similar.

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