pH Test Strip Reading Ambiguity

[A Single Step]

Following Cyb's Max Ion, and I have 125g MHRB and 40g NaOH in 2L distilled water. It felt magical and somewhat ominous as I added the lye solution to the citric acid (~2 pH) / bark mix and watched it change from wine colored to gray to black. Reminded me of the black liquid in the Scarlet Johansson film Under the Skin or scenes out of Ridley Scott's Prometheus.

I tried testing the pH using a meter that worked well for making the citric acid solution, but gave erratic results with the base solution. I think I broke the meter because there was some remnant of the xylene used for defating and it hasn't worked since it was exposed to that while attempting to measure the base solution.

I tried using pH strips (plastic type): I pipetted a sample, and set in front of fan to reduce the xylene remnant. But there is still some smell of it. The test strip comes out pretty much black -- off the scale on the side of the bottle. Doesn't change when I try to rinse it under running water.

It seems the black tint of the solution is interfering with the pH strip testing. Maybe the xylene is too.

Endlessness wrote that the mixture turning black is indication that your at a sufficiently high pH. Would others concur with that?

 

[downwardsfromzero]

Strong base and/or solvents, indeed, easily will destroy some pH probes.

Endlessness is right about the solution turning black acting as a pH indicator in and of itself. It doesn't really take that much base to do the trick and personally I've never used a pH meter during a plant extraction.

To test a strongly colored solution using a pH strip you could take your drop of alkaline solution and dilute it in a small amount of distilled water, then use a drop of the diluted solution to drip onto the strip. This will reduce the amount of interference from the color of the solution.

 

[A Single Step]

Endlessness is right about the solution turning black acting as a pH indicator in and of itself. It doesn't really take that much base to do the trick and personally I've never used a pH meter during a plant extraction.

Thanks for the reassurance.

To test a strongly colored solution using a pH strip you could take your drop of alkaline solution and dilute it in a small amount of distilled water, then use a drop of the diluted solution to drip onto the strip. This will reduce the amount of interference from the color of the solution.

But won't diluting the solution reduce the pH that you're testing?

 

[rido]

Yes, it will. But remember that pH is a logarithmic scale. This page explains the math and chemistry behind it: https://www.chem.purdue.edu/gchelp/howtosolveit/Equilibrium/Calculating_pHandpOH.htm

This means that a solution of pH 12.0 is about half as basic as a solution of pH 12.5. This 0.5 difference is beyond the accuracy of a pH strip.

 

[A Single Step]

Thanks, Rido. Thanks Downwards.