Abstract
Measurements of parameters expressed in terms of carbonic species such as Alkalinity and Acidity of saline waters do not analyze the influence of external parameters to the titration such as Total free and associated Carbonic Species Concentration, activity coefficient, ion pairing formation and Residual Liquid Junction Potential in pH measurements. This paper shows the development of F5BC titration function based on the titrations developed by Gran (1952) for the carbonate system of natural waters. For practical use, samples of saline waters from Pocinhos reservoir in Paraiba were submitted to titration and linear regression analysis. Results showed that F5BC involves F1x and F2x Gran functions determination, respectively, for Alkalinity and Acidity calculations without knowing "a priori" the endpoint of the titration. F5BC also allows the determination of the First and Second Apparent Dissociation Constant of the carbonate system of saline and high ionic strength waters.
Highlights
Surface waters and groundwaters in the Northeast semi – arid region of Brazil are classified as high ionic strength waters
CT in saline waters is represented by the sum of the carbonate species such as carbonic gas, CO2, total bicarbonate, HCO3T- and total carbonate, CO32-T
In the development of F5BC function are obtained some data of F1x and F2x modified Gran functions that allows the determination of Alkalinity and first dissociation constant of the carbonate system
Summary
Surface waters and groundwaters in the Northeast semi – arid region of Brazil are classified as high ionic strength waters. When the linear fraction of each plot is extrapolated to a function value equal to zero, the corresponding value of the strong base added is equal to the necessary volume to titrate back to the equivalence point under research This is the way to determine Alkalinity and Acidity or one of its forms. Function F5BC allows the determination of Acidity and Alkalinity of saline waters and incorporates activities effects and ion pairing formation. Calibration of the electrode is carried out just prior to an experiment using buffer solution of [7,10] and [9,25] at 25°C, respectively, and pH 7,10 ± 0.1 At this temperature, constant increments (0, 5 ml) of strong base (NaOH) with a precisely known molarity are added until the pH= 9, 0. In this way the system can accommodate volume changes and still remain essentially isolated from the atmosphere
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