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I have a tool where I point it at something, and it gives me an RGB value. I want to add universal indicator to a liquid, measure the RGB value and input it into the site to find the pH. Does anyone have any ideas?

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  • $\begingroup$ How accurate do you need the pH to be? $\endgroup$ – f'' Jul 17 '16 at 6:06
  • $\begingroup$ @f'' preferably more accurate than being using a pH chart and eyes, $\endgroup$ – SuperNinja741 Does Gaming Jul 17 '16 at 6:11
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    $\begingroup$ pantone.com/capsure-formula-guide-bundle This kind of thing would give you an accurate colour reading in RGB/CMYK, however if you have access to a lab etc, a UV-VIS spectrometer would be far superior at measuring the colour at which your solution absorbs $\endgroup$ – NotEvans. Jul 17 '16 at 10:12
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    $\begingroup$ Actual color is dependent on the light you reflect, ie you need to calibrate the white balance. It sounds like a lot of work for nothing $\endgroup$ – Greg Jul 17 '16 at 13:13
  • $\begingroup$ RGB values vary non-linearly with the concentration of the light-absorbing substance. So I doubt you will find a tool that's easy to use and that will provide a higher accuracy than the colour matching charts that come with indicator kits. Also for measuring RGB values you'll probably run into problems with the gamut of the measurement device. $\endgroup$ – aventurin Jul 17 '16 at 22:15
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Your best bet would be to prepare 15 solutions of buffers at pH 0, 1,.. 14 and calibrate your instrument. Dip three different test papers in each solution, get average numbers. Normalize colors and see the r/g, r/b, and g/b ratios for each pH. Now you can just make a long if statement in excel and plug your measured numbers there.

Fill excel with 15 statements like
=if(r/g > 5 and r/g <8 and r/b>3 and r/b<3.5; "pH=3"; "")

Also, many pH papers come with a map of colors for each pH. you can use that for calibration.

The thing is, chemists use pH meters when they need accurate readings. accuracy down to mili-pH is achievable. pH meters are build on very different principles and are reasonably priced.

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