Cation concentration

Dissolution of Calculi Model. Dissolved Ions from Ca3(PCf)2. Dissolution of calcium phosphate by macrocyclic polyamines proceeds at pH 7, which is established by measuring the freed cation concentration as well as the freed anion concentration with respect to the control values (Table 7). The molar ratio of [Ca2 + ] to [P04 ]... 

Electroneutrality requires that the total cation concentration must equal total anion concentration and hence, taking account of charge numbers,... 

Wash solutions for precipitates, 426 Washing of precipitates 118, 426 by decantation. 119 solubility losses in, 119, 427 Washing soda D. of sodium carbonate in, 295 Water absorbents for, 477 ammonia-free, 679 deionised, 90 D. of hardness, 332 D. of total cation concentration, 210 D. with Karl Fischer reagent 637 distilled, 90 high purity, 91 ionic product of, 36 types and standards for, (T) 90 volume of 1 g at various temperatures, (T)87... 

Polar organic solvents readily precipitate exopolysaccharides from solution. The solvents commonly used are acetone, methanol, ethanol and propan-2-ol. Cation concentration of the fermentation liquor influences the amount of solvent required for efficient product recovery. In the case of propan-2-ol, increasing the cation concentration can lead to a four-fold reduction in die volume of solvent required to precipitate xanthan gum. Salts such as calcium nitrate and potassium chloride are added to fermentation broths for this purpose. 

Polymers like those in the poly aniline family interchange protons and anions with the solution, allowing a local modulation of pH. Composites that interchange cations allow the modulation of any cation concentration. Efforts are being devoted to the synthesis of polymer or polymeric derivatives having great cationic specificity. 

The emf depends on the concentrations of the ions, as we explore later here we have reported the value observed when the two solutions have equal cation concentrations.) In this case, the electrons can be thought of as tending to travel... 

Once a layer-silicate clay forms, it does not necessarily remain in the soil forever. As conditions change it too may weather and a new mineral may form that is more in equilibrium with the new conditions. For example, it is common in young soils for the concentrations of cations such as K, Ca, or Mg in the soil solution to be high, but as primary minerals are weathered and disappear, cation concentrations will decrease. With a decrease in solution cations, a layer-silicate such as vermiculite will no longer be stable and can weather. In its place. 

Figure 16-1 is a master-variable diagram corresponding approximately to the previous clean marine case, illustrating that HC03 derived from CO2 is only important at pH > 7, and that at equilibrium H", NH4, and SO4- are the dominant species. Figure 16-2 extends this approach to the small population of droplets without any SO - in them that are nucleated on particles of seasalt that is present. In this case, pH = 6.7 and the dominant cation is seawater "alkalinity" or Ak (alkalinity in seasalt is the sum of cation concentration due to dissolved... 

For aqueous potassium hydroxide (10 M) the value of the observed rate coefficient is 226 I.mole Fsec at 0.1 °C. Over the temperature range 0.1 to 20.6 °C an activation energy of 6.0 kcal.mole was calculated. At zero cation concentration ko (0.1 °C), obtained by extrapolation, has a value of 6.0 l.mole . sec with an associated activation energy and entropy of 9.1 kcal.mcle and — 24 cal.deg. mole respectively. 

Wahl et al ° have suggested that the rate coefficient obtained by the nmr method" at cation concentrations 5x 10 M is that for the step k2 in the above mechanism. There is reasonable agreement between the data obtained by these two different procedures. A comparison has been made of the experimental results with those obtained from the Marcus theory °. 

Table 7. Cation concentrations in cell-wall fluid centrifiiged from Vigna hypocotyls...

The effect of pH and cation concentration on pectinesterase (PE) activation and permeation on 30 kD MWCO ultrafiltration (UF) membrane was evaluated. In order of increasing effectiveness, PE activity was stimulated by monovalent and divalent cations, poly amines and trivalent cations. A similar trend was observed for permeation on UF membranes. Cation addition and higher pH releases PE from an inactive complex, increases activity, and increases permeation. Higher cation concentration decreases activity and permeation. These results suggest a common mechanism is involved in PE activation and permeation. 

Activation studies were conducted at pH 7.5 at 30°C in 20 mL of 0.5% high methoxyl citrus pectin (Citrus Colloids, Hereford, U.K.). Final cation concentration in PE extracts used for activation studies was less than 2 mM as measured by potentiometry. Controls were conducted to correct for non-enzymic alkali consumption, with no polyamine/no PE and polyamine added/no PE. PE activity was normalized as a percentage of activity with no cation addition. 

The concentration of cations at discrete pH values which resulted in the highest observed PE permeability was obtained at pH 8.0 and 0.15M NaCl, pH 3.8 and 0.4M NaCl, or pH 3.8 and O.IM CaCl2. An increase of pH and/or cation concentration promoted an increase in PE permeability. Conversely, flux decreased with an increase in cation concentration or pH. At similar pH and cation concentrations that stimulate PE activity by competitive displacement, permeation of PE through a 30 kD MWCO UF membrane was observed. At low pH and no salt, the low level of pectin present in the PE extracts bound PE and prevented permeation. 

The experimental results are presented by plotting A[H30+], the loss of protons from the pectic ionic sites, against the ratio [Me2+]t/Cp where [Me +Jt and Cp are the total cation concentration (equiv.l-i) and the pectin concentration (equiv. COO-.l- ), respectively. 

The experimental results obtained by measuring ions activity after equilibration with pectins are plotted as binding isotherms [Me +Jb/Cp vs [Me +Jt/Cp where [Me2+]b is the bound cation concentration at equilibrium (equiv.l-i) calculated from measured activity using previously calculated activity coefficients. 

When Ca and K are added to y-A203 the a parameter does not change. No new additional peaks appear in the spectra for cation concentrations up to 20 at.%. This shows that K and Ca cations do not diffuse into the alumina bulk... 

Diffusion in Binary Electrolytes at Nonzero Currents Consider a reaction in which one of the ions of the binary solution is involved. For the sake of definition, we shall assume that its cation is reduced to metal at the cathode. The cation concentration at the surface will decrease when current flows. Because of the electroneutrality condition, the concentration of anions should also decrease under these conditions (i.e., the total electrolyte concentration c. should decrease). 

Since the membrane is permeable for cations but not for the anions A, it should intrinsically contain anions R . When these are fixed, their concentration, Cr, will remain the same everywhere. Hence in layers ( J,) and (ii) the overall cation concentration should also be the same, and the diffusion potential (which is caused by a possible difference in cation mobilities) is extremely small. In the left-hand part of the membrane system, the concentration of cations M + in each of the phases is equal to the given (invariant) concentration of anions A or, respectively the potential difference between the phases is determined, according to Eq. (5.10), by the cation concentration ratio. The right-hand part of the membrane system corresponds to the system (5.22), where phase (P) now takes the place of phase (a), and phase (rj) takes that of phase (y). As a result, we obtain for the membrane potential. 

Osmotic swelling is a second type of swelling. Where the concentration of cations between unit layers in a clay mineral is higher than the cation concentration in the surrounding water, water is osmotically drawn between the unit layers and the c-spacing is increased. Osmotic swelling results in larger overall volume increases than surface hydration. However, only certain clays, like sodium montmorillonite, swell in this manner. 

FIG. 7 Plots of the increase of water concentration in NB (A[H20]) with extraction of cations with DPA against the equilibrium cation concentration in NB. Each value in the parentheses shows the number (n) of coextracted water molecules per ion. (From Ref. 46. Copyright 1997 American Chemical Society.)... 

The saturation of the SHG response at high cation concentrations suggests that the process of complex formation at the membrane surface may be treated by a Langmuir-isotherm type analysis [24,27]. At constant temperature, the Langmuir equation is given by... 

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