October 22, 2020, 10:58:21 AM
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Topic: Using Newton-Raphson Method for pH of Aqueous Acidic Solution  (Read 3727 times)

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Offline Mark S 2014

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I'm just coming to the conclusion of this weeks lab report. In one part of the experiment I completed two titrations, one of 0.1 M HCl vs 0.2 M NaOH and one of 0.1 M Acetic acid vs 0.2 M NaOH. I had to compare my experimental titration curves against theoretical titration curves generated using the Newton-Raphson method, but only for between 0-12 mL of NaOH added, so just before the equivalence point.

I  calculated the percentage errors between theoretical and experimental pH levels in each and they are pretty high, in the acetic acid titration my experimental pH levels are mostly between 40-60 % higher than theoretical, in the HCl titration they are between 5-20 % different.

I'm trying to tie things up by speaking about why this massive difference might be. Its my first time using this method and I can't seem to think of a way to explain this. Can anybody give me an idea or push in the right direction of why these large differences are seen  ?

Offline Arkcon

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Re: Using Newton-Raphson Method for pH of Aqueous Acidic Solution
« Reply #1 on: March 22, 2015, 09:58:50 AM »
This is a pretty tough question, so kudos to your academic program for teaching it to you.  OK, relying only on Wikipedia, you attempted to find the correct function, in this case a titration curve, by estimating, and repeatedly determining the derivative.

Let's work with the titation of HCl and NaOH, that should be an easy to understand curve.  What did you write as an approximate curve?  And what curve did you determine experimentally?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline Borek

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Re: Using Newton-Raphson Method for pH of Aqueous Acidic Solution
« Reply #2 on: March 22, 2015, 11:12:27 AM »
Can you show us plots of both theoretical and registered curve?
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