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Field measurement of alkalinity and pH

Water Supply Paper 1535-H

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Abstract

The behavior of electrometric pH equipment under field conditions departs from the behavior predicted from Nernst's law. The response is a linear function of pH, and hence measured pH values may be corrected to true pH if the instrument is calibrated with two reference solutions for each measurement. Alkalinity titrations may also be made in terms of true pH. Standard methods, such as colorimetric titrations, were rejected as unreliable or too cumbersome for rapid field use. The true pH of the end point of the alkalinity titration as a function of temperature, ionic strength, and total alkalinity has been calculated. Total alkalinity in potable waters is the most important factor influencing the end point pH, which varies from 5.38 (0 ? C, 5 ppm (parts per million) HC0a-) to 4.32 (300 ppm HC0a-,35 ? C), for the ranges of variables considered. With proper precautions, the pH may be determined to =i:0.02 pH and the alkalinity to =i:0.6 ppm HCO3- for many naturally occurring bodies of fresh water.

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Field measurement of alkalinity and pH
Series title:
Water Supply Paper
Series number:
1535
Chapter:
H
Edition:
-
Year Published:
1964
Language:
ENGLISH
Publisher:
U.S. G.P.O.,
Description:
17 p. :ill. ;24 cm.