Finding order of a reaction- how do I make an excess of iodine

Point out if i'm wrong please

If a reaction takes the form:

1A + 1B --> 1C + 1D

and I want to measure the order of the reaction with respect to A, I need to:

1.

1. Make sure there is an excess of ALL other reactants, so that the concentration of them can be modelled as constant? (I assume so)

2.

2.Measure the amount of time taken for all of A to be used (or other end-point)?

assuming 1. is correct, what is the definition of 'excess'? 10x more moles of B than A, 100x?

And if this is true, and I am using an Iodine solution which has a maximum possible concentration of 0.02mol dm^-3, and all the rest have concentrations above 1mol dm^-3, how do I manage to create a solution which has excessive moles of iodine? I'd need a ratio of like 500:1 of iodine to all other reactants, and this just isn't practical.

Hence i think i must have misunderstood something

Reply 1

Kyle_S-C

12

You could just dilute the other solutions, but it really sounds like you're meant to be identifying the order of the reaction with respect to iodine...

Reply 2

hai2410

OP

11

Kyle_S-C

You could just dilute the other solutions, but it really sounds like you're meant to be identifying the order of the reaction with respect to iodine...

Need to find the entire rate equation, not just with respect to iodine. Was the ... significant? I think i'm mainly confused because nobody else in my lab seems particularly phased by this issue. Not sure if that means they've solved it, or just don't realise its there.

Reply 3

Kyle_S-C

12

hai2410

Need to find the entire rate equation, not just with respect to iodine. Was the ... significant? I think i'm mainly confused because nobody else in my lab seems particularly phased by this issue. Not sure if that means they've solved it, or just don't realise its there.

You could do something less exciting like dilute the more concentrated ones to 0.04M, 0.02M, 0.01M etc. and see how the rate changes then alter the concentration of iodine similarly?

And the ... was just a bad habit of mine.

Reply 4

hai2410

OP

11

Just in case anybody might have a look at this who needs help: basically you don't have to worry too much about excess iodine as the reaction is zero order with respect to it. Just figure that out, then after that the reaction doesn;t matter too much.

Finding order of a reaction- how do I make an excess of iodine

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