Dissociation of carbon acids

The insolubility of calcium carbonate is clearly evident from the value of the solubility product, Ksp, in water at 25°C Ksp = 8.7 x 10-9. The carbonate ions are produced in seawater by the dissociation of carbonic acid that forms from the... 

On the whole, when synthesizing a global model of the C02 biogeochemical cycle, the unit to simulate that part of the cycle spent in the ocean must describe how the ocean carbonate system works. Alekseev et al. (1992), analyzing the system C02 IICO, COj and the distribution of pH values in ocean waters, discovered that more than 80% of dissolved carbon dioxide is in the form of hydrocarbonate ion of HC03. This means that when synthesizing a model of the ocean carbonate system only the first stage of the dissociation of carbonic acid can be reliably considered. As a result, the flux of C02 dissolved in the upper layer of the ocean can be calculated by the formula... 

A common OH scavenger in natural waters is alkalinity. Alkalinity is a measure of the total carbonate concentration. This is complicated by the equilibrium that exists in natural waters produced by the dissolution of atmospheric C02 to produce carbonic acid, and the dissociation of carbonic acid. 

In case of acid solution this water correction is omitted, as the present acid suppresses to a sufficient degree the dissociation of carbonic acid which is the cause of the conductivity of the conductance water. On measuring the conductivity of alkaline solutions the correction may also be neglected. 

Bicarbonate is much more suitable as a major environmental water pH buffer. Its parent acid is H2C03, which is diprotic (Fig. 1.11). The dissociation of carbonic acid is described as follows ... 

Q3 The cells which produce HC1 are the parietal cells acid secretion can produce a stomach pH of 1.5-2. H+ is secreted into the stomach lumen by an ATP-dependent proton pump in exchange for K+. H+ secretion depends on the dissociation of carbonic acid, formed by the hydrolysis of C02, in a reaction catalysed by carbonic anhydrase ... 

Because carbonic acid is a weak acid, its dissociation in water is poor and thus the second dissociation takes place only to a negligible extent. Nevertheless, the dissociation of carbonic acid gives an acidic nature to water in natural systems. This is further analyzed in the Example 6.4. 

From the equilibrium equation for the first dissociation of carbonic acid... 

Given that the second dissociation is much smaller than the first one, we will consider that the HCO/ does not dissociate further and thus there is no other source of protons. Then, this is the predominant carbonate ion. Furthermore, we will also consider that the amount of protons provided by the self-dissociation of water is much smaller than that provided by the first dissociation of carbonic acid. In this way,... 

Some aqueous models accept only total inorganic carbon rather than titration alkalinity or carbonate alkalinity. For this reason, the sea water analysis of Table III includes total inorganic carbon which was calculated from pH, total alkalinity and salinity using the apparent sea water constants of Mehrbach et al.(82) for the dissociation of carbonic acid and the boric acid dissociation constant of Lyman (83), as expressed by Li et al. (84). 

Dissociation of carbonic acid gas.—This simple apparatus serves also to show another decomposition, one not less remarkable than that of water vapor the decomposition of carbonic acid gas at high temperatures. 

Idea of chemical equilibrium. It differs from the idea of medianical equilibrium, page 58.-46. The chemical equilibrium may be the common limit of two oppositely directed reactions. Phenomena of etherification, 58.— 47. Reciprocal actions of two soluble salts in the midst of a solution, 55.—48. Many chemical systems seem incapable of possessing a state of equilibrium which is the common limit of two reciprocally inverse reactions, 66.— 49. Grove s experiment. Water is decomposable by heat, 57.—50. Direct demonstration of the dissociation of water, 57.—51. Dissociation of carbonic acid gas, 59.-52. These decompositions are not complete but limited at the temperatures at which they are produced, the inverse reaction also takes place, 59.—53. Example of a state of equilibrium which is the common limit of two reactions the Inverse of each other. Action of water vapor on iron and the inverse action, 61.—54. Changes of physical state give rise to equilibrium conditions of which each is the common limit of two modifications the inverse of each other. 

Dickson A. G. and Millero F. J. (1987) A comparison of the equilibrium constants for the dissociation of carbonic acid in seawater media. Deep-Sea Res. 34, 1733—1743. 

Cycloalkenes.—Oyekan and Dent have recently published volumetric, i.r., and kinetic studies for several cycloalkenes on ZnO. Cyclopentene (pAa <= 44) produced predominantly only a vr-bonded species the failure to observe a TT-allyl species was predictable as ZnO cannot catalyse dissociation of carbon acids with pA a > 36. Cyclobutene appeared to undergo ring opening immediately upon adsorption and gave an i.r. spectrum that was very similar to that produced from buta-1,3-diene. Methylenecyclobutane rapidly produced an initial i.r. spec-... 

The hydration reaction (1.11), coupled with the first dissociation of carbonic acid (1.9), produces an apparent pK of 6.1 for bicarbonate formation. Thus, the summation of Equations (1.9) and (1.11) yields... 

The simple models of cation exchange presented here have not yet considered as a competing cation, even though it is always present in clay-water systems. cations are produced by water dissociation or, more importantly (because carbonic acid is more acidic than water), by the dissociation of carbonic acid formed from the dissolution of CO2 in water ... 

Problem Consider a calculation of the pH and extent of hydrolytic exchange that results when 1.0 g of Na -smectite is placed into 1.0 liter of distilled water that is open to the atmosphere. The smectite has a CEC of 0.9 mmole/g. Two reactions involving protons (3.56 and 3.59) must be considered. The first, which describes the dissociation of carbonic acid to form bicarbonate and a proton, has an equilibrium condition given by equation 3.58. The second is the exchange of Na" " from the clay by... 

The dissolution of CO2 in water and the dissociation of carbonic acid can be expressed by the following equations ... 

Substance 19 and water are the products of the dissociation of carbonic acid this is carbon dioxide. The answer is (B). 

The presence of CO2 influences the pH of an aqueous phase, due to formation mid dissociation of carbonic acid. The resulting pH is equal to values of about 2.9 at 200 bar and 40°C (9). The dissolution of metals in water determines die extent of leaching and extraction. To study the pH... 

Problem 9.44. Write equations for the dissociation of carbonic acid, H2CO3, in water. Ans. 

In addition to the phase behavior and the mixing state of the water/C02 biphasic system, the pH value must be considered as an important process parameter. In general, the system has quite an acidic nature due to the formation and dissociation of carbonic acid (Scheme 1). The second dissociation, of bicarbonate to a proton and carbonate, lies far to the left and does not contribute strongly to the pH value. Typically, the pH of unbuffered water at elevated pressures of CO2 is in the range of 2.8-3.0 [19]. 

Carbonate chemistry was incorporated into the model in order to verify realistic geochemical conditions. First, the carbonate chemistry is characterized by the dissociation of carbonic acid yielding HCO3 and COf. The two dissociation constants K,. and K2c are defined as follows... 

Because the pH of seawater is higher than in blood (7.35-7.45), however, the second dissociation of carbonic acid cannot be neglected and CO3 becomes an important aqueous species. 

Essentially, the suggested mechanism includes metabolic production of carbon dioxide, hydration to carbonic acid, catalysis by carbonic anhydrase, dissociation of carbonic acid, and exchange of the hydrogen ions for sodium ions across the luminal border of the cell. 

---