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Topic: pH paper doesn’t change its color  (Read 304 times)

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Offline songmalkang

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pH paper doesn’t change its color
« on: April 28, 2021, 07:45:23 PM »
summary.
pH probe indicate 7.5~9.5 (low at night high at day), pH Paper indicate 7.5 (all time)



Hi guys. I’m new guy in Dev cop. which makes industrial IoT service (like gas, fluid leaking detection).


Recently I start project for pH sensor network.

I gather quite dirty water from backyard and put it in top floor for testing red tide photosynthesis and organism makes pH Higher.

It does change pH ( The probe shows When Night, it goes 7.4 and daytime it slowly spikes up to 9.5 ).

For make sure my test, I bought pH paper from TOYO Roshi Cop. and soak it in testing fluid

But pH paper doesn’t change its color at 9.5. Just green like it's 7.0


I’m electronic engineer so im quite dumb at chemicals.

Heres what I did to find reason.

1. Put salt and Sugar into dirty water for Ionic strength stronger. (It doesn’t work. I thought this is the reason why pH paper doesn’t dye)

2. Cover The pH probe and water with dark cloth for stop photosynthesis. ( pH probe keep shows 7.5 )

3. Soak Probe into buffer solution to testing sensors, and It was accurate. (Cleaned with Desalted water)

4. Use 4 different sensor ( Different model, code, measuring method and all shows pH is 9.5 )


I don’t have any clue :(
« Last Edit: April 28, 2021, 08:01:14 PM by songmalkang »

Offline Borek

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Re: pH paper doesn’t change its color
« Reply #1 on: April 29, 2021, 02:42:31 AM »
What kind of pH paper do you use?

Universal ones - those for whole pH range - have often very slight color changes, quite easy to miss unless you are comparing two side by side.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline songmalkang

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Re: pH paper doesn’t change its color
« Reply #2 on: April 29, 2021, 05:59:02 AM »
Thanks for reply mate. I use universal one(0~14)

But in there color chart, 9~10 pH shows blue(with little purple)

I checked your advise And tested again. But It seems not different :(

The paper shows complete green(7) when actual pH is 9.5

Maybe I Need to add some picture for others ( about my dirty water bottle with red tide and the paper )

And again, Thanks for posting reply :D

Offline Borek

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Re: pH paper doesn’t change its color
« Reply #3 on: April 29, 2021, 09:19:13 AM »
As you are working with a rather narrow pH range some more specific pH papers should do better, they come in many different types and in my experience universal ones are good only for getting a very general idea of what is going on.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Youyin Bai

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Re: pH paper doesn’t change its color
« Reply #4 on: May 10, 2021, 10:19:03 AM »
First make sure your pH paper has not lost its power

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