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Topic: How do I use pH to find the rate law for a titration reaction?  (Read 1042 times)

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Offline mundane-morning

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I did a lab where I titrated HCl with NH4OH and measured pH every 2 secs. This was done with 1M each, 1M HCl/2M NH4OH, and 2M HCl/1M NH4OH.

For determining the rate law/rate orders I know I can compare the ratio of reaction rates between trials to the ratio of concentration between trials (eg. if rate doubles as concentration of HCl doubles the reaction is first order with respect to HCl).

 But I’m a little unclear on how to calculate rate of reaction from my pH data. Do I do change in [H+]/time for the time it takes to reach equilibrium? Or just for the initial spike? Or something else?

It may just be my data is not great and isn’t illustrating a clear rate order

Thank you!

Offline Borek

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Re: How do I use pH to find the rate law for a titration reaction?
« Reply #1 on: April 10, 2023, 03:14:39 PM »
Acid/base (neutralization) reactions are way too fast for determining their kinetics with titration methods - on the titration timescale they are instantaneous and limited by mixing.
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Offline mundane-morning

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Re: How do I use pH to find the rate law for a titration reaction?
« Reply #2 on: April 10, 2023, 03:30:06 PM »
Acid/base (neutralization) reactions are way too fast for determining their kinetics with titration methods - on the titration timescale they are instantaneous and limited by mixing.

That would make sense cause the data really doesn’t work out. The assignment is to determine the rate law though, so I’m unsure what the teacher wants… The only other data available is temperature over time which I used to determine enthalpy or reaction.

And there’s no way to determine rate law just based on the balanced reaction, correct? I’m pretty sure it has to be experimentally determined

Offline Borek

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Re: How do I use pH to find the rate law for a titration reaction?
« Reply #3 on: April 10, 2023, 05:01:05 PM »
I’m unsure what the teacher wants…

Neither do I.

Quote
And there’s no way to determine rate law just based on the balanced reaction, correct? I’m pretty sure it has to be experimentally determined

Yes.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

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