Solution chemistry ionic strength

Worked example 5.7 — soil solution chemistry ionic strength and activity coefficients... 

Activity depends on the ionic strength of the solution. If we compare a 1 M solution and a 0.01 M solution, the more concentrated solution may act as though it is less than lOOx more concentrated than the dilute solution. It is then said that the activity of the 1 M solution is less than unity or the activity coefficient is less than 1. For solutions with positive deviations from Henry s Law, the activity coefficient will be greater than 1. For very dilute solutions (low ionic strength) the activity coefficient y approaches 1, so concentration is approximately equal to activity for very dilute solutions. We will use concentrations in the calculations in this text instead of activities, but the approximation is only accurate for dilute solutions (<0.005 M) and for ions with single charges. Details on activity corrections can be found in most analytical chemistry texts, such as the ones by Harris or Enke listed in the bibliography. 

In I960, the "pH convention" was adopted by the International Union of Pure and Applied Chemistry, in response to the need for a consistent series of standards to define the pH scale (56). It was agreed that the activity coefficient of chloride ion in aqueous buffer solutions at ionic strengths no greater than 0.1 would be defined by... 

In most natural waters actinides are usually coordinated with hydroxide and carbonate ligands however, waters from ancient salt formations that are proposed as disposal sites for nuclear waste, such as the Waste Isolation Pilot Plant (WIPP) in New Mexico or the Gorleben site in Germany, are saturated with chloride salts. Chloride has been shown to affect the solubility and speciation of actinides significantly compared with their chemistry in inert electrolyte solutions ofsimilar ionic strengths. Radiolytic formation of hypochlorite in chloride brines may resnh in (he... 

Over the last several years, the number of studies on application of artificial neural network for solving modeling problems in analytical chemistry and especially in optical fibre chemical sensor technology, has increase substantially69. The constructed sensors (e.g. the optical fibre pH sensor based on bromophenol blue immobilized in silica sol-gel film) are evaluated with respect to prediction of error of the artificial neural network, reproducibility, repeatability, photostability, response time and effect of ionic strength of the buffer solution on the sensor response. 

Ranee, G.A. and A.N. Khlobystov, Nanoparticle-nanotube electrostatic interactions in solution the effect of pH and ionic strength. Physical Chemistry Chemical Physics, 2010. 12(36) p. 10775-10780. 

The effect of solution chemistry on the speciation of the organic contaminant 1-naphtol (1-hydroxynaphthalene) and its complexatiom with humic acid is reported by Karthikeyan and Chorover (2000). The complexation of 1-naphtol with humic acid (HA) was studied during seven days of contact, as a function of pH (4 to 11), ionic strength (0.001 and 0.1 M LiCl), and dissolved concentration (DO of 0 and 8 mg L ) using fluorescence, UV absorbance, and equilibrium dialysis techniques. In a LiCl solution, even in the absence of HA, oxidative transformation of 1-naphtol mediated by was observed. In addition, the presence of humic acid in solution, in the absence of DO, was found to promote 1-naphtol oxidation. These reactions are affected by the solution chemistry (pH, ionic strength, and cation composition). 

Fig. 16.20 Fluorescence quenching (FQ) of 1-naphthol in the presence of HA as a function of pH and reaction time (1-naphthol = 8pmol LHA = 11 ppm C ionic strength of O.IM LiQ) F and F denote fluorescence intensities in the absence and in the presence of the quencher (HA), respectively. Reprinted with permission from Karthikeyan KG, Chorover J (2000) Effects of solution chemistry on the oxidative transformation of 1-naphtol and its complexation with humic acid. Environ Sci Technol 34 2939-2946. Copyright 2000 American Chemical Society...

The ionic strength of the solution also plays an important role [16]. As represented in Fig. 16, the electrostatic interactions between substrate and particles are eliminated at a smaller distance in the case of a thin double layer (high ionic strength), which leads to a better removal efficiency. This feature highlights the limitation of the use of diluted chemistries. 

This effect of ionic strength on solution rate constants is very important in studying reactions relevant to atmospheric chemistry. Thus care must be taken to study the effects of ionic strength over a range that... 

Initiation with X = OH has been discussed earlier. Table 8.11 summarizes some of the aqueous-phase HO, chemistry in which OH is generated and reacts in the atmosphere. (Note that the rate constants for some of the aqueous phase reactions shown in Tables 8.10-8.16 depend on such factors as ionic strength see Chapter 5.D.) Involved with this chemistry is that of bicarbonate/carbonate, since OH reacts with these species as well (Table 8.12). It is interesting that, in contrast to the high reactivity of OH toward S(IV) in aqueous solutions, direct reactions of H02/02 with S(IV) do not appear to be important (Sedlak and Hoigne, 1994 Yermakov et al., 1995). 

We begin with a discussion of the most common minerals present in Earth s crust, soils, and troposphere, as well as some less common minerals that contain common environmental contaminants. Following this is (1) a discussion of the nature of environmentally important solid surfaces before and after reaction with aqueous solutions, including their charging behavior as a function of solution pH (2) the nature of the electrical double layer and how it is altered by changes in the type of solid present and the ionic strength and pH of the solution in contact with the solid and (3) dissolution, precipitation, and sorption processes relevant to environmental interfacial chemistry. We finish with a discussion of some of the factors affecting chemical reactivity at mineral/aqueous solution interfaces. 

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