Carbonate equilibrium with bicarbonate

Carbon dioxide is, of course, in equilibrium with bicarbonate ion almost the entire CO2-HCO3- system can be removed by heat or vacuum treatment (Smith 1964). The oxygen content of pasteurized bottled... 

Rainwater and snowmelt water are primary factors determining the very nature of the terrestrial carbon cycle, with photosynthesis acting as the primary exchange mechanism from the atmosphere. Bicarbonate is the most prevalent ion in natural surface waters (rivers and lakes), which are extremely important in the carbon cycle, accoxmting for 90% of the carbon flux between the land surface and oceans (Holmen, Chapter 11). In addition, bicarbonate is a major component of soil water and a contributor to its natural acid-base balance. The carbonate equilibrium controls the pH of most natural waters, and high concentrations of bicarbonate provide a pH buffer in many systems. Other acid-base reactions (discussed in Chapter 16), particularly in the atmosphere, also influence pH (in both natural and polluted systems) but are generally less important than the carbonate system on a global basis. 

Any body tissue in direct equilibrium with the major excretum should reflect the isotopic composition of the diet as a whole. This seems to be the case for bioapatite carbonate, which is thought to be in equilibrium with plasma bicarbonate, which itself is in equilibrium with respired CO2. In fact the Ambrose and Norr (1993) and Tieszen and Fagre (1993) data sets (among others) show clearly that the bioapatite carbonate differs from total diet (or respired CO ) by an amount approximating to the equilibrium isotopic fractionation in the system (Mook 1989) ... 

At equilibrium, the concentration of H+ will remain constant. When a strong acid (represented by H+ or HA) is introduced into solution, the concentration of H+ is increased. The buffer compensates by reacting with the excess H ions, moving the direction of the above reaction to the left. By combining with bicarbonate and carbonate ions to form the nonionic carbonic acid, equilibrium is reestablished at a pH nearly the same as that existing before. The buffer capacity in this case is determined by the total concentration of carbonate and bicarbonate ions. When no more carbonate or bicarbonate ions are available to combine with excess H+ ions, the buffer capacity has been exceeded and pH will change dramatically upon addition of further acid. 

In water the bicarbonate ion is in equilibrium with carbonic acid ... 

Figure 6-6 also shows the variation in the partial pressure of carbon dioxide in equilibrium with the lagoon s waters. The average value of this pressure exceeds the atmospheric value, 1, so on average, carbon dioxide is evaporating from the lagoon. The evaporation rate is greatest at times of maximum alkalinity and bicarbonate concentration and minimum carbonate ion concentration. 

Figure 6-8 shows how the partial pressure of carbon dioxide in equilibrium with surface water oscillates in phase with the fluctuations in precipitation rate, saturation state, and temperature. The oscillations in alkalinity and bicarbonate concentrations have shifted in phase by about 90° because these quantities decrease when precipitation and evaporation are removing carbon from the system at above-average rates. 

Although C02 is a normal metabolite, it is toxic at elevated levels. C02 exists in equilibrium with carbonic acid (H2C03) and with bicarbonate (HCO, ), a major H+ buffer. Renal conservation of HCO, is generally sufficient to buffer hypercapnia however, an added insult, such as... 

Almarsson 6, Kaufman MJ, Stong JD, Wu Y, Mayr SM, Petrich MA, Williams MJ. Meropenem exists in equilibrium with a carbon dioxide adduct in bicarbonate solution. J Pharm Sci 1998 87 5. 

Acid Hydrolysis. The water that enters soil as rain or snow is in equilibrium with CO2 in the atmosphere, which dissolves to form carbonic acid. Unpolluted rainwater has a pH of approximately 5.7, whereas water in soil pores may be exposed to air containing a higher partial pressure of CO2 than the free atmosphere, and hence soil water may be more acidic (see Section 5.4). It is the attack on soil minerals by this weak carbonic acid that is the major chemical weathering process in most soils. For example, acid hydrolysis of calcium carbonate yields calcium and bicarbonate ions ... 

At this stage of development the model is restricted to a constant pH reactor and considers only two (pH and volatile acids concentration) of the five variables considered important for monitoring digester operation. This restriction of constant pH can be removed and the model extended to incorporate the interaction with bicarbonate alkalinity by considering the carbon dioxide-bicarbonate equilibrium as shown in Equations 16 and 17. 

For fresh waters there is a further restraint on pH rise the CO2 reservoir of the atmosphere. For a given pco2 the pH is a function of alkalinity. In order to raise the pH of a water in equilibrium with the atmosphere from 8 to 9, alkalinity must increase by nearly 5 meq liter (either by base addition or by evaporation). Hence only soda lakes, that is, lakes containing substantial amounts of soluble carbonates and bicarbonates, can attain high pH values for example, Sierra Nevada spring waters discharged to the east of the Sierra and evaporated in a plaza of the California desert. 

Mechanisms of calcium carbonate deposition. The carbonate of shell has its origin in the bicarbonate of the medium (Hammen and Wilbur, 1959), metabolic CO2 (Campbell and Speeg, 1969), or in some cases from calcium carbonate spherules present in the tissues (Watabe et al., 1976). In marine bivalves, bicarbonate probably comes chiefly from the medium (Wheeler et al., 1975). The principal source of shell calcium is the medium with tissue spherules providing a secondary supply. The CaCOs of molluscs is thought to be deposited in isotopic equilibrium with the medium (Milliman, 1974). However, discrimination in favour of C and 0 has been observed (Keith et al., 1964 Tourtelot and Rye, 1969), and this discrimination may be different in aragonitic and calcitic layers. 

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