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topic 6096

Total, Free and phenolphthalein Alkalinity


Q. Total, free and phenolphthalein Alkalinity. The Hach manual (and I am sure others do as well) shows how to measure these. Does anyone have information on alkaline silicated aluminum cleaners and what the upper and lower limits for these alkalinities needs to be and why?

Mike McGinness
CPSSCO - S.Houston, Texas


Q. Does anyone know the equation used to determine free and total alkalinity for determination of an unknown using a known standard? I know there is a general equation but I cannot remember what it is.

Richard Alexander Robles
- Monterey Park, California, United States

Bicarb vs Acetate

May 9, 2016

Q. I've got a question about if acetate interferes with measuring Alkalinity in produced water. We use Standard Method 2320B for measuring Alkalinity, which is a titration method, and I'm going to assume you are already familiar with it. Depending on the beginning pH of the sample, we titrate first to pH 8.3, and then to an endpoint of pH 4.5. Based on the volume and normality of the acid used for the titration, we extrapolate how much of the Alkalinity is due to Hydroxide, Bicarbonate, and Carbonate.

My question is: if there is acetate present in the water, will that interfere with the alkalinity titration?

When I first began researching it, I thought it would possibly cause a falsely elevate reading with Bicarbonate, but now as I was researching further, with bicarbonate being a weak acid and acetate being a weak base, I'm not sure what to make of it.

Kathy D
environmental lab employee - Riverton, Wyoming, USA

May 12, 2016

A. Acetate is alkalinity. You can eliminate it by titrating to a methyl orange endpoint.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

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