Reaction between KMnO4 and Ethanedioic acid

Maniachris

I'm studying this reaction for my practical coursework and my results seem dodgy,
what should the rate of reaction be with respect to ethanedioic acid and potassium manganate(VII)?
any help would be much appreciated.

what sort of reaction are you talking about? you didn't even specify what are you reacting with? I know you have ethanedioic acid and KMnO4, but is there something else?

Reply 2

OP

The reaction is between pottasium manganate and ethanedioic acid. the ethanedioic acid is dissolved in disttilled water and the potassium manganate is dissolved in sulphuric acid.
Here's the information I should of put to start with: the Mn2+ ions are produced which act as a catalyst to the reaction which is autocatalytic. So therfore i'm guessing that the rate of reaction with respect to potassium manganate should be of order 1 or 2, i'm not sure which.
With respect to ethanedioic acid, I'm guessing that it should be order 1.

This is the equation :
2MnO4−(aq) + 6H+(aq) + 5(CO2H)2(aq) goes to 2Mn2+(aq) + 10CO2(g) + 8H20(l)

Reply 3

OP

UPDATE:
My results seem to suggest that the rate with respect to ethanedioic acid is 0 as for time interval 50-60 seconds the change in absorbance is always close to 0.12 for every concentration of ethanedioic acid, (the purple colour of the manganate dissapears as the reaction progresses).
Im not sure if this is right as my results are generally very dodgy.
Another problem is is that I did not test the changing absorbance of the reaction for varying concentrations of potassium manganate (my teacher did not suggest it and I was too stupid to realise I should) so my results give no clue as to what the rate of reaction with respect to it should be.

Reply 4

Maniachris

The reaction is between pottasium manganate and ethanedioic acid. the ethanedioic acid is dissolved in disttilled water and the potassium manganate is dissolved in sulphuric acid.
Here's the information I should of put to start with: the Mn2+ ions are produced which act as a catalyst to the reaction which is autocatalytic. So therfore i'm guessing that the rate of reaction with respect to potassium manganate should be of order 1 or 2, i'm not sure which.
With respect to ethanedioic acid, I'm guessing that it should be order 1.

This is the equation :
2MnO4−(aq) + 6H+(aq) + 5(CO2H)2(aq) goes to 2Mn2+(aq) + 10CO2(g) + 8H20(l)

You don't guess the orders, that is why the kinetics of a reaction is determined experimentally. Have you done the experiments?

Reply 5

OP

When I said that i'm guessing them, I didn't mean that I would seriously apply my guesses to my write-up report - I ment for someone to comment on the guesses as to whether they sound correct.
As to whether i've done the experiments to find the orders of the reactants, I have but only for ethanedioic acid, but I have very dodgy results and when I plot the rate of reaction of each concentration at a specific time interval I get little to no correlation.
Unless you could comment as to what you think the orders with respect to potassium manganate and ethanedioic acid should be, there is no point commenting on this thread.

Reply 6

Maniachris

When I said that i'm guessing them, I didn't mean that I would seriously apply my guesses to my write-up report - I ment for someone to comment on the guesses as to whether they sound correct.
As to whether i've done the experiments to find the orders of the reactants, I have but only for ethanedioic acid, but I have very dodgy results and when I plot the rate of reaction of each concentration at a specific time interval I get little to no correlation.
Unless you could comment as to what you think the orders with respect to potassium manganate and ethanedioic acid should be, there is no point commenting on this thread.

Hmm, sorry to have upset you. However, dodgy results are down to poor experimental techniques. Repeating the experiments a lot more times would have improved your dodgy results. And as for any rate of reaction experiments, the rate could be proportional to any of the starting materials, so essentially, you should really have found out how changing the concentration of each of the starting materials can affect the rate. That final advice is for your future use.

Reply 7

OP

Surely though you could predict the rate of reaction with respect to each of the starting chemicals given that you know the chemical equation? (ive already given the equation)
Is there any chemical theory out there which states how the rate of reaction would vary with respect to the the chemical responsible for the autocatalysis, in this case potassium manganate, and the other chemicals in this given reaction?
Surely there must be some reason behind experimental evidence, to say that the rates can be only determined experimentally doesn't make much sense to me. It's like saying 'oh well that happens... just because it does'.

Reply 8

Rubs

I was doing something about rates a couple of days ago for a problem sheet and the book clearly said (something along the lines of):

Rates can only be determined experimentally and cannot be determined from the stochiometric equation.

For some products you can have a rough idea, i.e. if you have a decomposition you know that it will probably cause a rate-determining/slow step. Some of your reactants might not affect the rate at all in this equation, whereas they might iwith another reaction but there's no way of knowing that by looking. You could try researching the reaction online.

Reply 9

Maniachris

Surely though you could predict the rate of reaction with respect to each of the starting chemicals given that you know the chemical equation? (ive already given the equation)
Is there any chemical theory out there which states how the rate of reaction would vary with respect to the the chemical responsible for the autocatalysis, in this case potassium manganate, and the other chemicals in this given reaction?
Surely there must be some reason behind experimental evidence, to say that the rates can be only determined experimentally doesn't make much sense to me. It's like saying 'oh well that happens... just because it does'.

Yes, indeed especially for Sn1 and Sn2 chemistry reactions, there are hell lots of confusions between them, as some reactions tend to have a mixture of both going on, especially dealing with secondary alcohol/halogenoalkane.

You can probably PREDICT what mechanism it goes through, therefore PREDICT whether it is unimolecular(sn1) or bimolecular(sn2) reactions, but you dont' know for sure till experimental results proved this.

Reply 10

Joeeeee75

rate=k[KMnO4(aq)][C2O4H2(aq)]the Hydrogen atoms in Ethanedioic acid moot, as they don't appear in the reation equation.NB this is for neutral conditions, not sure about the effect of the Mn2 autocatalyst, its probably second order, but don't quote me on that.It is important to stress that rates and orders CANNOT be deduced from the balanced equation, you can only find the rate of a step in a proposed mechanism experimentally.

Reply 11

jhnikhnknh