pH question

[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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