pH question

[kelemvor]

Given the price, you could probably just replace the phenol red reagent. I believe it's this one: http://www.amazon.com/Taylor-Replace.../dp/B0002IXIL8 for $2

[CarlD]

Did you neutralize the chlorine before running the lab test? Though, high chlorine usually makes pH look high.

Is Taylor still using the self-neutralizing phenol reagent, or is it the non-neutralizing agent? If your chlorine levels are high try adding a drop of the neutralizer to the Taylor test--I THINK it's bottle #7 and see if the results are more consistent.

Also, this is a rare case where I'd double check with either a Hach or LaMotte brand test strip and see which it confirms...if you have the strips around.

[chem geek]

Taylor's phenol red solutions have a special balance of neutralizers in them that are somewhat pH neutral. They do not recommend adding thiosulfate solution since that can raise the pH itself. If you have a water sample with more than 10 ppm FC, then you can measure its pH by diluting the sample with unbuffered (distilled or deionized) water. Do not use tap water or other buffered water as it will affect the pH.

[PoolDoc]

Carolina, please retest the pool with both the K2006 and the lab meter. But, when you carry the sample into the lab, make sure there's no air space in the sample bottle. And, dilute your POOL sample 50:50 with distilled water before testing.

Also, tell us what your free chlorine level is -- phenol red doesn't usually deteriorate, but if you convert it to chlorophenol red by very high FC (>10ppm) levels, you can get false readings.

This chart:

from http://isbchem1.pbworks.com/w/page/9206118/pH%20Review shows the different ranges -- but the colors are not very accurate.

You can compare the actual end-point colors in these pictures from
http://www.titrations.info/acid-base...rs-preparation

Chlorophenol red:


Phenol red:


In my experience, the chlorophenol red endpoint (reached before 7.0!) is more violet than shown.





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