Bicarbonate-carbonate system

In Fig. 8.3, the measured pH-values of the investigated lakes are grouped by frequency. Two ranges of pH values appear in the recent investigation, one at pH 6 to 8 and a second at pH 2.5 to 4. Also seen from the literature (Pietsch 1979 Harvey 1980), a third pH range is revealed and a combined picture of all measured pH-values shows a three-modal frequency distribution. The ranges of pH-values and the concentrations of dissolved Al and Fe reflect the buffering potential of mainly three systems the bicarbonate/carbonate system, the Al(OH)x system, and the Fe(OH)x system. 

The autoregulation of the carbon cycle, which maintains the COj of the atmosphere at a constant level, depends on the one hand on the COg— bicarbonate-carbonate system of the air, seas and sediments, and on the other hand it depends on photosynthesis, the intensity of which is regulated by the concentration of available COg. 

The solution concentration for a potassium carbonate system is limited by the solubility of the potassium bicarbonate (KHCO3) in the rich... 

The important buffer system of blood plasma is the bicarbonate/carbonic acid couple ... 

Under the conditions of temperature and ionic strength prevailing in mammalian body fluids, the equilibrium for this reaction lies far to the left, such that about 500 CO2 molecules are present in solution for every molecule of H2CO3. Because dissolved CO2 and H2CO3 are in equilibrium, the proper expression for H2CO3 availability is [C02(d)] + [H2CO3], the so-called total carbonic acid pool, consisting primarily of C02(d). The overall equilibrium for the bicarbonate buffer system then is... 

Carbonates and bicarbonates are used as lower alkalinity adjuncts or substitutes for hydroxide. It has been suggested that hydroxide/carbonate systems are more resistant to carbonation during spraying than hydroxide-only solutions. Powder products blended with light sodium carbonate are much less hygroscopic, and the carbonate can be a useful carrier for liquid additives, such as surfactants and solvents. 

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. 

A mixture of sodium hydroxide and sodium carbonate, a metering pump being necessary. This method avoids the use of either silicate or phosphate and is popular for woven goods and in circumstances where silicate would pose problems. Ideally the carbonate should be free from bicarbonate. This system has less buffering capacity and gives slightly lower bath stability than methods (1) and (2). 

This reaction is essential in maintaining a constant pH in blood by the bicarbonate buffer system. Carbonic anhydrase, which contains a single zinc atom in its structure, has a molecular weight of about 30,000. In this structure, zinc is surrounded tetrahedrally by three histidine molecules and one water molecule. The exact role of the catalyst is not known, but it is believed to involve hydrolysis that can be represented as... 

The identification of different carbonate binding modes in copper(II) and in zinc(II)/2,2 -bipyridine or tris(2-aminoethyl)amine/(bi)carbonate systems, specifically the characterization by X-ray diffraction techniques of both r)1 and r 2 isomers of [Cu(phen)2(HC03)]+ in their respective perchlorate salts, supports theories of the mechanism of action of carbonic anhydrase which invoke intramolecular proton transfer and thus participation by r)1 and by r 2 bicarbonate (55,318). 

Tissue culture, more frequently used as cell culture, enables animal and plant cells to be cultured in large numbers by techniques comparable to those used in microbiology but, because of the fragile nature of the cells, does require special cultural conditions. The culture media used must supply all the essential factors for growth, such as a wide range of amino acids, nucleotides, enzyme co-factors as well as indeterminate factors that can only be supplied in special products, e.g. foetal bovine serum. The environmental conditions must be carefully controlled, particularly pH, and this is frequently maintained by culturing in a bicarbonate buffer system and a carbon dioxide saturated atmosphere. 

Tosh, J. S., J. H. Field, H. E. Benson and W. P. Waynes, "Equilibrium Study of the System Potassium Carbonate, Potassium Bicarbonate, Carbon Dioxide and Water," U. S. Bureau of Mines, Report of Investigations, 1959, 5484. 

Isotope equilibrium exchange reactions within the inorganic carbon system atmospheric CO2 - dissolved bicarbonate - solid carbonate lead to an emich-ment of 13C in carbonates. 

The carbonic acid-bicarbonate buffer system has a of 6.1, yet is still a very effective buffer at pH 7-4 because it is an open buffer system, in which one component, CO2, can equilibrate between blood and air. 

The composite pA of the bicarbonate system, 6.1, may appear to make it ill-suited for buffering blood at physiologic pH of 7.4. Nevertheless, the system is very effective at buffering against additions of noncarbonic acids. Changes in the bicarbonate/carbonic acid ratio in such cases can be regulated by ... 

Daily body activities are quite sensitive to large pH changes, and must be kept within a small range of H30 and OH concentrations. Human blood, for example, has a pH of approximately 7.4 maintained by a buffer system. If our blood pH drops below 7.35, it can cause symptoms such as drowsiness, disorientation and numbness. If the pH level drops below 6.8, a person can die. To maintain pH stability, there is a carbonic acid - bicarbonate buffer system in the blood. 

Demineralization, like the zeolite process, involves ion exchange. The metal ions are replaced with hydrogen ions by means of the process and equipment described for the hydrogcn-zcolitc system (see Hot Lime Zeolite—Split Stream Softening, previously described). In addition, the salt anions (bicarbonate, carbonate, sulfate and chloride) are replaced by... 

Na2HP0 solution (NAP) (140 mg/L), to provide a solution containing an inorganic complexing agent to form anionic species with reduced technetium (9). This anion was used instead of carbonate, as the purification system of the anaerobic chamber removes CO from the atmosphere, and a bicarbonate-carbonate solution would not be stable. 

Only a few of the reactions summarized in Table 3.3 are actually based on data at subzero temperatures. In most cases, the lower temperature for data is 0°C. This could potentially be a serious limitation for the FREZCHEM model. For example, quantifying carbonate chemistry requires specification of Ah,co2 -ftcb - 2 and Kw all of these reactions are only quantified for temperatures > 0 °C (Table 3.3). Figure 3.9 demonstrates how six of the most important relationships of Table 3.3 extrapolate to subzero temperatures. We were able, based on these extrapolations, to quantify the solubility product of nahcolite (NaHCOa) and natron (Na2CO3 10H2O) to temperatures as low as — 22°C (251 K) (Marion 2001). Even for highly soluble bicarbonate and carbonate minerals such as nahcolite and natron, their solubilities decrease rapidly with temperature (Marion 2001). For example, for a hypothetical saline, alkaline brine that initially was 4.5 m alkalinity at 25 °C, the final alkalinity at the eutectic at —23.6°C was 0.3m (Marion 2001). At least for carbonate systems it is not necessary to extrapolate much beyond about —25 °C to quantify this chemistry, which we believe can reasonably be done using existing equation extrapolations (Fig. 3.9). 

The radical "OH in surface waters is quickly consumed by organic compounds, bicarbonate, carbonate, and nitrite. It has a typically low steady-state concentration of around 10"16 M. For this reason it cannot be directly detected, and quantification in laboratory experiments is usually carried out by means of reactions of known kinetics. The formation of phenol from benzene, of 4-hydroxybenzoic from benzoic acid, and the disappearance of nitrobenzene are suitable systems if intermediate monitoring is carried out by liquid chromatography, while the disappearance kinetics of butyl chloride is suitable for headspace sampling and gas-chromato-graphic analysis [64]. 

Thode H.G., Shima M., Rees C.E. and Krishnamurty K.V. (1965) Carbon-13 isotope effects in systems containing carbon dioxide, bicarbonate, carbonate, and metal ions. Can. J. Chem.. 43, 582-595. 

Blood travels through the human body in more than 96,000 km of blood vessels and it is full of marker molecules [34], The physiological pH is usually 7.4 with a complex buffer system (bicarbonate-carbonic acid, hemoglobinate-hemoglobin, phosphate buffer) [35],... 

Effect of Holding One s Breath on Blood pH The pH of the extracellular fluid is buffered by the bicarbonate/carbonic acid system. Holding your breath can increase the concentration of C02(g) in the blood. What effect might this have on the pH of the extracellular fluid Explain by showing the relevant equilibrium equation(s) for this buffer system. 

Again, buffers are essential in keeping pH within defined limits so that biochemical reactions can occur with maximum efficiency (i.e. maintaining so-called homeostasis). If, for example, the pH gets too low, the acidic environment can damage (or denature) and thus disable enzymes. An important example is the buffering of blood by the carbonic acid-bicarbonate buffer system illustrated below ... 

The Carbonate System. Since no osmotic or activity coefficient data are available for single salt solutions of carbonate and bicarbonate salts, estimates had to be made of the activities of these ligands in solution, as well as for the activities of carbonate and bicarbonate salt cations. 

In the carbonate system, the total alkaliiuty species has been identified as composed of the constituent species carbonate ion, bicarbonate ion, and hydroxide ion. To express all these constituent species in terms of a single parameter, total alkalinity, they need to be expressed in terms of the number of equivalents. Thus, if the concentrations are in terms of equivalents per liter, they can all be added to sum up to the total alkalinity, of course, also in terms of equivalents per liter. 

The acid-base equilibria between carbonate/bicarbonate/carbon dioxide clearly show that in vivo systems sufficient amounts of CO2 will be present such as to allow reactions to occur and point out the relevance of the reactivity of COj with biologically significant compounds. The carbonate radical anion is a strong oxidant the reacts by either H-atom abstraction or electron transfer (Eo(C03, H /HCOj) = 1.78V, where the former is generally slower than the latter. 

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