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Our teacher said.....for this book

Page286....

His Question is, calculate the three endpoints in page 286.

For the P.286, I take some pics.below....

(3) Geochemical or charge-balance definition (8.38) where BC are base cations (principally Na+. K+. Ca2. Mg). and SA are strong acid anions (principally CI SO) Of course, the three definitions define essentially the same property of water, but each emphasizes a different aspect of alkalinity, respectively: () the way we measure alkalinity: (2) the chemical species that comprise it; and (3) the fact that alkalinity in natural waters arises from an imbalance between the biogeochemical processes giving rise to strong base cations and strong acid anions As described in the first definition, alkalinity is a capacity term: the sum of titratable bases to two endpoints defined in reference to the carbonate system: (1) pH 8.3, were all carbonate has been titrated to bicarbonate and essentially all hydroxide alkalinity if any was present in the sample, has been converted to water; and 2) pH 4.5-5.1 where all bicarbonate has been tirated to H2CO. The second endpoint is defined by a plI range because the pl of the equivalence point depends on the concentration of H2CO present at that point. In turn, his depends on the initial alkalinity, as well as thec extent to which the sample is stirred to relcase CO2 to the atmosphere. If operational factors like the degree of stirring are constant, samples with high alkalinity will have high concentrations of H2C(): at the equivalence point, and the higher IH-C(치 is, lhe lower the plI wl be. Standard Methods2 gives the following endpoint plI values for different lkinies: Total alkalinity Endpoint as CaCO meq/I. 0.6 30 150 4.9 4.6 10.0 Figure 8.4 shows an idealized titration of the carbonate system for a solution initially containing 1 x M Na2CO3 and illustrates some importanl conditions for measuring alkalinity. The quanity o acid required to reach the lirst cndpoint caled V determines the carbonate alkalinity of a sample. This quantity sometimes is called the phenolphthalcin alkalinity. in referenee to the color indicator commonly used to detect the endpoint. The total quantity of acid required to reach the second end point. called V2. gives the total alkalinity of a sample, and the difference between Vi and V2 gives the hicarhonate alkalinity. The color indicator usually sed lo delermine V2 is a mixture of bromcresol green and methyl red (color change from green to pink to red), hul V2 also is determined by (D plotting the titration curve (as in Figure 8.4) and determining the inflection point. (2) titrating to a fixed plI (see values tabulated above). or (3) Gran plots (see Section 8.5.3). The total alkalinity thus is the sum of the carbonate and bicarbonate alkalinity. Waters with pll8.3 have no titratable carbonate alkalinity In these cases, which are very common, alkalinity. It is important to note that the inflection points marking the two endpoints (especially that for the second one) in the carbonate titration are much less sharp than the inflect point or strong acids and bases shown in Figure 8.1. As the carbonate he icrbonale alkalinity is equal tco 12 0.0 0.5 10 1.5 2.0 2.5 3.0 3.5 Concontration of strong acid addod, 10-3 M Figure 8.4 Titration of I x 103 M Na2CO, with strong acid. V occurs at the first inflection point, and V2 at the second

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14 ej en 2- Lt So Itre CosCas e st Phosphat bA

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