Temperature carbonate solubility constants

Carbonate alkalinity is not a directly analyzable quantity, but it can be derived from the titration alkalinity (A ) by a relationship which is temperature and pressure dependent. pH is also variable with pressure and temperature. In addition, pH can be defined several ways depending on which buffer system is used, whether liquid junction potentials are considered, and what definition of ionic strength is used. The values of the apparent dissociation constants and calcium carbonate solubility constants are dependent on exactly what definition of seawater pH is used and what standardization technique is used (15, 16, 17). 

The Change in Apparent Calcium Carbonate Solubility Constants with Temperature (After Horse et al. (35))... 

The interfacial tension of the binary system a-tocopherol/carbon dioxide was measured using the pendant drop method in the pressure range between 10 and 37 MPa at nine different temperatures 313, 333, 343, 353, 363, 373, 383, 393 and 402 K. The interfacial tension decreases with rising pressure at a constant temperature and increases with increasing temperature at a constant pressure. The interfacial tension was found to be mainly a function of the mutual solubility of the two system components and of the density of pure carbon dioxide. 

Because of difficulties in precisely calculating the total ion activity coefficient (y) of calcium and carbonate ions in seawater, and the effects of temperature and pressure on the activity coefficients, a semi-empirical approach has been generally adopted by chemical oceanographers for calculating saturation states. This approach utilizes the apparent (stoichiometric) solubility constant (K ), which is the equilibrium ion molal (m) product. Values of K are directly determined in seawater (as ionic medium) at various temperatures, pressures and salinities. In this approach ... 

The other approach employs a geochemical computer model, such as PHREEQC (Parkhurst 1995 also Chap. 15) with an input of a complete seawater analysis. Such a model will then calculate the activity coefficients and the species distribution of the solution according to the complete analysis and the constants of the thermodynamic database used. These constants are well known with an accuracy which is usually better than the accuracy of most of our analyses at least for the major aquatic species. Together with the real constant of the solubility product a reliable saturation index (SI = log Q) is then calculated. The constants of solubility products are not accurately known for some minerals, but for calcite, and also for most other carbonates, these constants and their dependence on temperature and pressure are very well documented. 

A plot of logio [Ni ]x versus pH showed that the corresponding solubility constant is almost independent of temperature at least in the range of 348.15 to 363.15 K. Apparently other neutral transition metal carbonates behave similarly. 

The solubility of CO2 in sea water is an important factor in controlling the exchange of carbon between the ocean and atmosphere. Henry s law (eqn [1]) describes the relationship between solubility and sea water properties, where S equals the solubility of gas in liquid, k is the solubility constant (k is a function mainly of temperature) and P is the overlying pressure of the gas in the atmosphere. 

The values of the solubility mole fractions are multiplied by a factor of 10 to the power of 6. This clearly shows that PVP qualifies as a sparingly soluble solute in comparison to the previously discussed PCM as not only are the saturation mole fractions lower, but also shifted significantly toward lower carbon dioxide mole fractions. The measured solubility data for PVP (40 kg mol ) in the system CO2/ EtOH and CO2 with different wt% ratios of EtOH to acetone are given in Fig. 24.13 (right), Eig. 24.14 (left), and Fig. 24.14 (right). The solvent composition was varied in terms of wt% of EtOH to acetone in between 70/30, 50/50, and 30/70. The temperature was set constant at 313 K and the pressure in the view cell was varied between 10, 13, and 16 MPa. 

No. 41 or 541 filter paper. Wash the precipitate first with warm, dilute hydrochloric acid (approx. 0.5M), and then with hot water until free from chlorides. Pour the filtrate and washings into the original dish, evaporate to dryness on the steam bath, and heat in an air oven at 100-110 °C for 1 hour. Moisten the residue with 5 mL concentrated hydrochloric acid, add 75 mL water, warm to extract soluble salts, and filter through a fresh, but smaller, filter paper. Wash with warm dilute hydrochloric acid (approx. 0.1M), and finally with a little hot water. Fold up the moist filters, and place them in a weighed platinum crucible. Dry the paper with a small flame, char the paper, and burn off the carbon over a low flame take care that none of the fine powder is blown away. When all the carbon has been oxidised, cover the crucible, and heat for an hour at the full temperature of a Meker-type burner in order to complete the dehydration. Allow to cool in a desiccator, and weigh. Repeat the ignition, etc., until the weight is constant. 

Figure 6.4 On the left is a phase diagram for carbon dioxide. Broken lines indicate isotherm crossing at either constant pressure or density. On the right is illustrated the change in solubility of naphthalene as a function of temperature and pressure.

The deprotection of carbobenzyloxy protected phenylalanine was carried out in a low-pressure test unit (V= 200 ml) equipped with a stirrer, hydrogen inlet and gas outlet. The gas outlet was attached to a Non Dispersive InfraRed (NDIR) detector to measure the carbon dioxide. During the reaction the temperature was kept at 25 °C at a constant agitation speed of 2000 rpm. In a typical reaction run, 10 mmol of Cbz protected phenylalanine and 200 mg of 5%Pd/C catalyst were stirred in a mixture of 70 ml ethanol/water (1 1). The Cbz protected phenylalanine is not water-soluble but is quite soluble in alcoholic solvents conversely, the water-soluble deprotected phenylalanine is not very soluble in alcoholic solvents. Thus, the two solvent mixture was used in order to keep the entire reaction in the solution phase. Twenty p.1 of the corresponding modifier was added to the reaction mixture, and hydrogen feed was started. The hydrogen flow into the reactor was kept constant at 500 ml/minute and the progress of the reaction was monitored by the infrared detection of C02 in the off-gas. 

Being able to change the density, via either changes in pressure or temperature, is the key difference in SFC over GC and LC separations. Typical density ranges are from 0.3 to 0.8g/ml for pure carbon dioxide. Table 16.2 shows data obtained from ISCO s SF-Solver Program for the calculation of density (g/ml), Hildebrand Solubility Parameter and a relative equivalent solvent for pure carbon dioxide at a constant pressure of 6000 psi, approximately 408 atm. 

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