Chemistry Kinetics Lab HELP

[chipu10]

Hi guys!

I need to do a kinetics lab in my chem class and i was thinking of doing it on concentration affecting the rate of reaction and using change in conductivity to prove it.

Unfortunately, i can't find a reaction that works. I've tried to google it and it just doesn't come up. If you know of a reaction that would work or have other ideas for the lab it would be very appreciated.

=]

[sweetnsimple786]

My teacher showed the class this website when he was teaching electrolysis. http://www.sparknotes.com/chemistry/electrochemistry/electrolytic/problems.html

Does the third problem help?

Maybe I'm misinterpreting "change in conductivity," but when you said that, this type of problem is what you reminded me of.

[Dr. Polaris]

Either what sweetnsimple said,

or do you mean as the conductivity gets higher, the more concentrated one thing is. In case I didn't make sense, ultra-pure water has a LOWWWWW conductivity. Low conductivity, low concentration.

anyways, I might be mixing things up.

[chipu10]

Either what sweetnsimple said,

or do you mean as the conductivity gets higher, the more concentrated one thing is. In case I didn't make sense, ultra-pure water has a LOWWWWW conductivity. Low conductivity, low concentration.

anyways, I might be mixing things up.

Yeah i mean that as i increase the concentration of a certain solution the reaction will happen faster thus increasing or decreasing (it doesnt matter i just need a change) the conductivity of the solution.

[Daedalus]

I think that this doesn't really have much to do with electrolytes, because when you have the two cells you're actually influencing the chemical reaction itself. Here you said you wanted to measure the effect of concentration, which makes sense. For example if you add a great deal of HCl to some calcium carbonate powder, you will get a very fast reaction. If you only add a little, you will get a slower one.

In the water of course the more ions you have the higher the conductivity, I think, so in the case of the higher concentration of HCl you would get a higher conductivity. But since you already know how much HCl you're adding and you can use that to calculate the concentration anyways, there doesn't seem to be much of a point...

edit: re-read your question. do you mean you want to measure the final products in a reaction based on a change in conductivity? possibly in this case HCl will be used up so conductivity will go down. But at the same time, it's much easier to collect the CO2 gas released.... which is probably true in most cases. Measuring the rate of reaction is usually based on one of the products, or possibly on the enthalpy (temperature) changes, etc.

[chipu10]

I think that this doesn't really have much to do with electrolytes, because when you have the two cells you're actually influencing the chemical reaction itself. Here you said you wanted to measure the effect of concentration, which makes sense. For example if you add a great deal of HCl to some calcium carbonate powder, you will get a very fast reaction. If you only add a little, you will get a slower one.

In the water of course the more ions you have the higher the conductivity, I think, so in the case of the higher concentration of HCl you would get a higher conductivity. But since you already know how much HCl you're adding and you can use that to calculate the concentration anyways, there doesn't seem to be much of a point...

edit: re-read your question. do you mean you want to measure the final products in a reaction based on a change in conductivity? possibly in this case HCl will be used up so conductivity will go down. But at the same time, it's much easier to collect the CO2 gas released.... which is probably true in most cases. Measuring the rate of reaction is usually based on one of the products, or possibly on the enthalpy (temperature) changes, etc.

The whole point f the lab is to study the factors that affect chemical reactions. I was looking into manipulating the concentration of a solution in a reaction that experiences a change in conductivity. So in this way i can measure the rate in which the conductivity changes and explain how concentration was the reason why the rate changed. My problem is that i cant seem to find a reaction that works.

Do you know of a reaction that has a significant change in ions? So there are either many ions to start with and little ions at the end or vise versa... This would mean a change in conductivity which is what i'm trying to measure.

[Daedalus]

I think that this doesn't really have much to do with electrolytes, because when you have the two cells you're actually influencing the chemical reaction itself. Here you said you wanted to measure the effect of concentration, which makes sense. For example if you add a great deal of HCl to some calcium carbonate powder, you will get a very fast reaction. If you only add a little, you will get a slower one.

In the water of course the more ions you have the higher the conductivity, I think, so in the case of the higher concentration of HCl you would get a higher conductivity. But since you already know how much HCl you're adding and you can use that to calculate the concentration anyways, there doesn't seem to be much of a point...

edit: re-read your question. do you mean you want to measure the final products in a reaction based on a change in conductivity? possibly in this case HCl will be used up so conductivity will go down. But at the same time, it's much easier to collect the CO2 gas released.... which is probably true in most cases. Measuring the rate of reaction is usually based on one of the products, or possibly on the enthalpy (temperature) changes, etc.

The whole point f the lab is to study the factors that affect chemical reactions. I was looking into manipulating the concentration of a solution in a reaction that experiences a change in conductivity. So in this way i can measure the rate in which the conductivity changes and explain how concentration was the reason why the rate changed. My problem is that i cant seem to find a reaction that works.

Do you know of a reaction that has a significant change in ions? So there are either many ions to start with and little ions at the end or vise versa... This would mean a change in conductivity which is what i'm trying to measure.

Here is one idea:

if you have 0.1M of acetic/ethanoic acid in a flask and 0.1M aqeous ammonia in another, you don't have much conductivity, since they are both weak (acid the first and base the other) and they are not very dissociated. But when they react together they form the salt ammonium acetate which is largely dissociated in water I think so it ends up conducting much better.

Edited December 9, 2010 by Daedalus

[chipu10]

I think that this doesn't really have much to do with electrolytes, because when you have the two cells you're actually influencing the chemical reaction itself. Here you said you wanted to measure the effect of concentration, which makes sense. For example if you add a great deal of HCl to some calcium carbonate powder, you will get a very fast reaction. If you only add a little, you will get a slower one.

In the water of course the more ions you have the higher the conductivity, I think, so in the case of the higher concentration of HCl you would get a higher conductivity. But since you already know how much HCl you're adding and you can use that to calculate the concentration anyways, there doesn't seem to be much of a point...

edit: re-read your question. do you mean you want to measure the final products in a reaction based on a change in conductivity? possibly in this case HCl will be used up so conductivity will go down. But at the same time, it's much easier to collect the CO2 gas released.... which is probably true in most cases. Measuring the rate of reaction is usually based on one of the products, or possibly on the enthalpy (temperature) changes, etc.

The whole point f the lab is to study the factors that affect chemical reactions. I was looking into manipulating the concentration of a solution in a reaction that experiences a change in conductivity. So in this way i can measure the rate in which the conductivity changes and explain how concentration was the reason why the rate changed. My problem is that i cant seem to find a reaction that works.

Do you know of a reaction that has a significant change in ions? So there are either many ions to start with and little ions at the end or vise versa... This would mean a change in conductivity which is what i'm trying to measure.

Here is one idea:

if you have 0.1M of acetic/ethanoic acid in a flask and 0.1M aqeous ammonia in another, you don't have much conductivity, since they are both weak (acid the first and base the other) and they are not very dissociated. But when they react together they form the salt ammonium acetate which is largely dissociated in water I think so it ends up conducting much better.

Oh that sounds good

i'll run that by my teacher tomorrow and see what he thinks

thanks!!

[Dzeb]

However, I don't believe that measuring conductivity will give you good results. To see the rate of reaction you would have to measure the rate of change of conductivity. I have tried to do a similar thing with pH but such changes are too quick to be measured.

The most precise and used method is to collect gases that are being released. For example, HCl + MgCO3 > MgCL + H2O + CO2 - you can measure the change in CO2 concentration which will give you the rate of reaction.

Any method that can measure a change in the concentration of products or reactants will do.

[Daedalus]

pH can be measured amazingly if you have data logging software and hardware available. Vernier Logger Pro is the software I know of... you can use it to plot titration curves and stuff.

But more importantly if you are doing conductivity change you don't necessarily need to measure the rate of change. It's fine to measure the degree of change after a certain interval - for example, if you measure the conductivity at 0/30/60 seconds for a reaction, speed it up, do the same thing, and so on, you will still get an indication of how they are changing. But then instead of getting five data points per graph of the conductivity vs. time of each reaction, you would plot rate of change of conductivity vs. concentration, and get at least 5 (preferably more) sets of concentrations measured.

gl

edit: also if the rate of reaction is simply too fast, add variables to slow it down. reduce concentration by a magnitude, or change surface area when using reactions involving solids, etc..

Edited December 9, 2010 by Daedalus

[Tilia]

I've done a similar lab and for some reason measuring conductivity was not a good way, but don't remember why.

My suggestion is that you let Mg react with HCl and check for the formation of gas.

[Stereoisomer]

What about the reaction; PCl3 + 3H2O --> H2PO3 - + 4 H + + 3 Cl -

We learnt about this reacton in class. Our chem teacher said this would be an ideal reaction using electrical conductivity as a technique because well, because we have to reactants with no charge, producing 3 products with a charge. Thus the electrical conductivity will most likely go from 0 to whatever (if the reaction proceeds).

I hope that helps!! im pretty sure i've also seen that equation from the IBID textbook, you might want to also check that

haha thanks

[Dzeb]

Sorry for repeating myself, but I don't want any of you to do work for nothing.

A change in conductivity is instant and you cannot measure the rate of this change. You will be able to measure the change in conductivity with the change in concentration. However, this will give you the degree of dissociation or smth, but not the rate of reaction.

Edited June 2, 2010 by Dzeb