Cation-exchange site

To elucidate the higher BE peaks [S(2p) 168.9, 169.6 eV], we examined the Naflon film Itself because It has -SOj" cation exchange sites. Only C(ls) and F(ls) peaks were observed. No S(2p]f peak was observed even after Ar" bombardment. This result suggests that the surface concentration of cation exchange sites Involving -SO3 Is low. Sulfur located well below the surface would, of course, hot be detected by XPS, We assign the higher BE S(2p) peak to a surface sulfate species (11),... 

P.C. Meier, W.E. Morf, M. Laubli, and W. Simon, Evaluation of the optimum composition of neutral-carrier membrane electrodes with incorporated cation-exchanger sites. Anal. Chim. Acta 156,1—8 (1984). 

Figure 4.10. Humus with cation exchange sites created by the ionization of phenolic and acidic functional groups. The M+ represent exchangeable cations.

Ammonium and hydrogen ions (protons) are both present in the soil solution as multielement cations. Ammonia gas reacts with water to produce the ammonium cation, NH4+ (Figure 5.8, equation 1). Ammonium acts as a cation in all senses and will be attracted to cation exchange sites on soil particles. Ammonium in the soil solution and on exchange sites is available to plants. 

This method does not measure exchangeable protons attached to cation exchange sites therefore, it is also common to use a salt solution (either KC1 or CaCl2) instead of distilled water in determining soil pH. The K+ or Ca2+ in the solution exchanges with exchangeable hydronium, thus bringing it into... 

Give both general and specific examples of how organic compounds can lead to the formation of cation exchange sites in soil. 

Soil pH is perhaps the most critical and common soil measurement where a definite amount of water is added before a measurement is made. Soil pH is a particularly complicated measurement because the proton can and does exist as a hydronium ion in the soil solution, as an exchangeable ion on the cation exchange sites, and bonded to various soil constituents. Because of these complexities, a soil sample is usually brought to a standard moisture content before a pH measurement is made. By bringing different soils to a common moisture content, they can be compared and analytical results from different laboratories will be comparable. Although there is a number of ways to measure soil pH, typically it is carried out using a pH meter and a pH electrode. 

If this is the case, pillared clay would have corresponding cation exchange capacity (CEC). The CEC values of these clays decreased to zero on intercalation with [A1- 304(0H)24(H20)i2] cations. Calcination increased CEC, although after calcination at 400°C. Al-sapo and Al-mont showed 0.35 and 0.13 meq.g of CEC, respectively. Thus, the difference in the acidity observed between Al-mont and Al-sapo seems to be attributable predominantly to the number of cation exchangeable sites generated on decomposition of pillars. 

I ) species with copper(II) which will not bind to the cation exchange sites. 

Adsorption to the K+-covered siloxane surfaces of the clay, illite, can be estimated using Eq. 11-20. A tnt.eda is 300,000 L mol-1 and the surface area factor, /saf, for illite is 6 (Table 11.2). Since the ground water contains so much calcium relative to potassium (30 1), only a very small fraction of the cation exchange sites on the illite are covered with weakly hydrated potassium ions you assume/K+clay is about 0.01. Thus, you estimate ... 

In a modification of the usual solvent extraction step, six triazines were successfully recovered using Cl8 cartridges and 250 mL samples, but terbutryn required a 0.25% NH3 (ammonia) washing step prior to elution with acetonitrile (Vitali et al., 1994). The authors ascribed this effect to secondary cation exchange sites in the solid phase. 

Uptake of137Cs from soil was also studied in the 1960s (Frederiksson et al., 1966) and there has been renewed interest in relation to the longterm effects of the Chernobyl accident. The uptake is very dependent on the type of soil. In normal agricultural soils, Cs, like K, is fixed on the cation-exchange sites in the clay fraction. Within plants, Cs is more mobile than Sr, and it is translocated more readily from leaves to seeds (Middleton, 1959). It can also be absorbed from the matt horizon at the top of the soil, as this comprises organic material, but uptake from normal soils becomes small once Cs is fixed on the clay fraction. In Table 2.21, the data for UK, US and Denmark shows that B only slightly exceeds bx + b2. 

Figure 2.32. Example of a mixed-mode sorbent consisting of silica modified with octyl (C8) alkyl chains and strong cation-exchange sites bonded on the same sorbent particle.

Figure 10.16 Conceptual model by Gardner et al. (1991) which suggests that while adsorption or cation-exchange sites will reduce the mobility of NH4+ in both sediment types, sea salts in estuaries should in effect neutralize the cation-exchange sites, thereby enhancing NH4+ diffusion and ultimately flux rates. (Modified from Gardner et al., 1991.)...

Sometimes these operationally defined procedures have a sound theoretical basis. For example, it is quite reasonable to suppose that leaching with magnesium nitrate solution will displace zinc from cation exchange sites in soils, or leaching with ammonium acetate will displace exchangeable calcium, magnesium, sodium, and potassium. Flame spectrometry, especially flame AAS, is widely used for the analysis of such extracts. 

Name the various cation exchange sites on clay minerals. 

The species distribution of the solution determines the cation composition of the interlayer space of montmorillonite. In equilibrium, the cation exchange sites of montmorillonite are covered by calcium, hydrogen, manganese, and sodium ions (Figure 2.9). Figure 2.13 shows the equivalent fractions (X) of these cations as a function of pH at the ratio of MrnEDTA =1 1. 

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