Phenolphthalein or metacresol purple may be used for alkalinity titration to pH 8.3.

вЂњPhenolphthalein alkalinityвЂќ is the term traditionally used for the quantity measured by titration to pH 8.3 irrespective of the colored indicator, if any, used in the determination. The pH values in Table 2320:I are suggested as the equivalence points for the corresponding alkalinity concentrations as miligrams CaCO 3 per liter. CO 2 concentration depends, in turn, on the have occured during titration. End points: When alkalinity is due entirely to carbonate or bicarbonate content, the pH at the equivalence point of the titration is determined by the concentration of carbon dioxide (CO 2) at the stage. Because this change in pH corresponds to an exact doubling of the hydrogen ion concentration, a simple extrapolation can be made to the equivalence point. The amount of standard acid required to reduce pH exactly 0.30 pH unit is measured carefully. 1 a.ДЇor samples of low alkalinity (less than 20 mg CaCO 3/L) use an extrapolation technique based on the near proportionality of concentration of hydrogen ions to excess of titrant beyond the equivalence point. For methods of determining inflection points from titration curves and the reationale for titrating to fixed pH end points, see Section 2310B. Alkalinity thus depends on the end-point pH used. Principle: Hydroxyl ions present in a sample as a result of dissociation or hydrolysis of solutes react with additions of standard acid.

Laboratory studies on mesophilic and thermophilic anaerobic sludge digestion. * Approved by Standard Methods Committee. Properly operating anaerobic digesters typically have supernant alkalinites in the range of 2000 to 4000 mg calcium carbonate (CaCO 3)/L. Raw domestic wastewater has an alkalinity less than, or only slightly greater than, that of the water supply. Alkalinity measurements are used in the interpretation and control of water and wastewater treatment processes. Alkalinity in excess of alkaline earth metal concentrations is significant in determining the suitablility of a water for irrigation. The measured values also may include contributions from borates phosphates, silicates, or other bases if these are present. Because the alkalinity of many surface waters is primarily a function of carbonate, bicarbonate, and hydroxide content, it is taken as an indication of the concentration of these constitutents.

Alkalinity is a measure of an aggregate property of water and can be interpreted in terms of specific substances only when the chemical composition of the sample is known.ДЄlkalinity is significant in many uses and treatments of natural waters and wastewaters. The measured value may vary significantly with the end-point pH used. It is the sum of all the titratable bases. DiscussionДЄlkalinity of a water is its acid-neutralizing capacity. Printing: Victor Graphics, Inc., Baltimore, MarylandД«inding: American Trade Bindery, Baltimore, MarylandД¬over Design: DR Pollard and Associates, Inc., Arlington, Virginia 2-24 2320 ALKALINITY * 2320 A. Printed and bound in the United States of America.Д¬omposition: EPS Group, Inc., Hanover, Maryland Standard methods for the examination of water and wastewater. The Library of Congress has catalogued this work as follows: No part of this publication may be reproduced, graphically or electronically, including entering in storage or retrieval systems, without the prior written permission of the publishers.

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