Phenolphthalein
By James McDonald, PE, CWT
Originally Published: CSTN – January 2004
What is Phenolphthalein Indicator? The Phenolphthalein Indicator is a pH
indicator solution that does not interfere with the water chemistries we are
checking. Phenolphthalein turns pink when the pH is above approximately
8.4 and turns clear when the pH is below approximately 8.4.
When you run the P- or OH-Alkalinity test, the Phenolphthalein lets you
know when the sulfuric acid has dropped the water pH to approximately 8.4
by changing from pink to clear.
When you run the sulfite test, the Phenolphthalein lets you know you’ve
added enough Acid Starch Indicator by changing from pink to clear. If the
water does not turn clear, add more Acid Starch Indicator.
When you run the neutralized conductivity test, the Phenolphthalein lets you
know when you’ve added enough Conductivity Neutralizing Solution by
changing from pink to clear.
Testing
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