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Topic: Neutralization Reactions  (Read 1078 times)

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Offline jkb2021

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Neutralization Reactions
« on: July 04, 2021, 01:19:39 PM »
I'm working on a lab for reaction rates of water/antacid and HCl/antacid.

I understand why water at various temperature react at different rates, but I don't understand why the neutralization reaction for HCl and and antacid takes almost as long as cold water.

Things I know:

In the acid-base reaction, HCl is a strong acid that fully dissociates. Bicarbonate is a weak acid and does not 100% accept H+.

Le Chatlerlier's principle states that when a stress is put on a system, equilibrium shifts to rebalance the system.

We aren't concerned with surface area, but it can have an effect. We were only watching the largest piece, however.


I can see that there would be much more free hydrogen ion in the acid-base solution. So maybe it just takes longer to fully neutralize compared to water, because the alka-seltzer bicarbonate Ion is only reacting with the hydrogen ion from citric acid and neutralizes more quickly.

Those aren't very satisfying answers. I just can't think of what about a neutralization reaction that would make it take longer. Is the activation energy significantly higher?

A point in the right direction would be welcome. :) 

Offline Borek

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Re: Neutralization Reactions
« Reply #1 on: July 04, 2021, 02:32:38 PM »
Can you elaborate on the lab details and procedures?

Neutralization reaction (understand as H++OH-) is very fast, I doubt you are able to measure it - so I suppose what you do measure is the kinetics of dissolution, or reaction at the surface.
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Offline jkb2021

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Re: Neutralization Reactions
« Reply #2 on: July 04, 2021, 02:41:17 PM »
It was a very simple lab, because we were not able to meet.

We had a cup of cold water, room temperature water, room temperature acid (HCl), and warm water (approx 30 C).

We just placed alka-seltzer tablets in the substances and timed how long it took the largest piece to fully dissolve.

 Reaction Rates:      
      
Solvent      Temperature   Time
      
Cold Water    < 23 C   2m:20s
      
Room Temperature 23 C   1m:10s
 Water   
      
Warm Water   30 C            43s
      
Room Temperature 23 C   2m:10s
HCl   

No calculations. The only question he had was to explain why the results were as expected and explain. Specifically he wanted to know why the results for the Acid make sense.

Going back to my OP, I understand the jist of acid-base chemistry, but I don't understand why it took so long. I probably answered it in my OP. I'm just not confident.
      

Offline Borek

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Re: Neutralization Reactions
« Reply #3 on: July 04, 2021, 03:49:12 PM »
For all practical purposes neutralization per se is instantaneous in such a setup, factors that are responsible for the reaction rate are mixing and dissolution (in other words you are transport limited).
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Offline jkb2021

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Re: Neutralization Reactions
« Reply #4 on: July 04, 2021, 04:47:46 PM »
For all practical purposes neutralization per se is instantaneous in such a setup, factors that are responsible for the reaction rate are mixing and dissolution (in other words you are transport limited).

I think you are misunderstanding. This is not rate of one mole reactants to one mole products. This is the time it takes to fully react/dissolve the tablet.

Because what you are saying if that the rate in which the tablet dissolved and the chemicals to fully react in each medium would be instantaneous, or for the sake of argument, one M/s. If that were the case, then it would not be a difference in time.

The professor has already verified that it is due to the acid-base reaction and that is what we are to address.

I feel like you are purposely trying to mislead me. In fact I think you responded to something last semester that ended up being completely wrong and going with my knowledge rewarded me full credit.


Offline Borek

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Re: Neutralization Reactions
« Reply #5 on: July 04, 2021, 05:34:55 PM »
For all practical purposes neutralization per se is instantaneous in such a setup, factors that are responsible for the reaction rate are mixing and dissolution (in other words you are transport limited).

I think you are misunderstanding. This is not rate of one mole reactants to one mole products. This is the time it takes to fully react/dissolve the tablet.

Yes, no misunderstanding here.

Quote
Because what you are saying if that the rate in which the tablet dissolved and the chemicals to fully react in each medium would be instantaneous, or for the sake of argument, one M/s. If that were the case, then it would not be a difference in time.

Process you observe consist of two separate parts: one is dissolution of the tablet (which you can easily observe) which is largely a physical change (especially in the case of a tablets that contains plenty of additional substances, like binder and fragrance additives), the other is the following chemical neutralization reaction. They are quite difficult to separate, but you don't observe the latter process in your experiment.

Quote
The professor has already verified that it is due to the acid-base reaction and that is what we are to address.

I am afraid it is much more complicated than that.

Quote
I feel like you are purposely trying to mislead me.

That's quite a serious accusation.

EOT
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