Dilute Aqueous Sodium Chloride Research Articles

A differential titration method for determining the dissociation characteristics of natural organic acids in the coastal zone

Characterizing the concentrations and equilibrium characteristics of organic acid/base pairs is essential for quantifying CO2-system components and their behaviors and interactions in organic-rich coastal environments. Relatively few studies have been devoted to characterization of titratable organics, and their contributions to total alkalinity are frequently implicitly or explicitly considered negligible. In this work, novel potentiometric titration procedures were developed to quantify the concentrations and dissociation constants of river-derived titratable organics and thereby their alkalinity (Org-Alk) contributions to the total alkalinity (TA) of coastal seawater. The overall approach was to compare the titration properties of two paired solutions of identical salinity (S ≈ 5): (a) a sample of “estuarine” water formulated as a mixture of organic-rich river water plus open-ocean seawater and (b) an organics-free “baseline” approximation of that estuarine water, formulated as a mixture of dilute aqueous sodium chloride plus open-ocean seawater. Acid was incrementally added to both solutions, and the resulting two titration curves were then compared to provide direct visualization and quantification of the contributions of organics to TA. In other words, at any given pH, the difference in acid added to the two solutions (with a small correction for silicate alkalinity) indicates acid uptake by titratable organics in the estuarine sample. This procedure was performed for four replicate samples at 15, 25, and 35 °C. Our titrations indicated the presence of three types of titratable organics. The dominant type had a concentration of approximately 200 μmol∙kg−1 and a well-defined dissociation constant (pK) that did not vary with temperature: pKOrg2(average) = 6.33 ± 0.01. The second type had a concentration of approximately 110 μmol∙kg−1 and a moderately well-defined and high pK: 8.56 ≤ pKOrg3 ≤ 9.32. The third type had a concentration of approximately 40 μmol∙kg−1 and a low, poorly defined pK: 4.1 ≤ pKOrg1 ≤ 6.1. Inference of this third type was required to eliminate systematic residuals that were otherwise present in our fitted titration data (residuals = direct observations – model predictions). These data allow for a summation of TA contributions from organic constituents that may contribute (especially in coastal waters) but are typically uncharacterized. Such data are required for rigorous CO2-system models that rely on inputs of the commonly used data pair of TA and dissolved inorganic carbon (DIC). Studies of CO2 system behavior in the coastal zone clearly require two types of alkalinity titrations – one that includes a summation of inorganic and organic components (i.e., conventional titrations), and a second CO2-free titration in which the concentrations and pK characteristics of organic acids are quantified.

Concentration Effects on the Spatial Interaction of Corrosion Pits Occurring on Zinc in Dilute Aqueous Sodium Chloride

The scanning vibrating electrode technique is used to study the localized corrosion of unpolarized zinc in near-neutral aqueous sodium chloride electrolyte of varying concentration [NaCl]. As [NaCl] is reduced from 1% (w/v) to 0.0005% (w/v) the morphology of attack changes from large, irregular, areas of anodic zinc dissolution and cathodic oxygen reduction, to a regular array of anodic pits set in an otherwise cathodic surface. In dilute electrolyte ([NaCl] < 0.01%) the total (area averaged) corrosion current density, J, (A·m−2), obtained from a numerical area integral of SVET anodic current density data, is shown to vary with approximately the square root of [NaCl]. The number density of pits, n (m−2) is shown to decrease with increasing [NaCl]. The mean individual pit current, , (A = J/n) varies with approximately the square root of [NaCl]. A simple geometric analysis, based on a calculation of the radial dependence of electrical resistance exhibited by a hemispherical shell of electrolyte concentric with the pit, is used to explain the relationship between ohmic potential drop in the external solution, solution conductivity, and the radial distance away from an existing active pit.

Traceable Thermodynamic Quantities for Dilute Aqueous Sodium Chloride Solutions at Temperatures from (0 to 80) °C. Part 2. The Quantities Associated with the Partial Molar Heat Capacity

In Part 1 of this two-part study (J. Chem. Eng. Data 2017, 62, 2617–2632), we presented fully traceable two-parameter Hückel equations (with parameters B and b1) for the activity and osmotic coefficients in dilute aqueous NaCl solutions in the temperature range (0 to 80) °C, and these equations apply within experimental error to almost all thermodynamic data existing in the literature and used in the tests at least up to a molality of 0.2 mol·kg–1. These data include also molar enthalpies of the components in the solutions. In our model, parameter B is treated as a constant whereas parameter b1 depends in a quadratic way on the temperature. No calorimetric data were used in the parameter estimation of the model. In this second part (Part 2) of the study, the results of the quantities associated with the heat capacity of NaCl solutions are considered. All heat capacity data available for NaCl solutions at least up to 0.2 mol·kg–1 can be predicted within experimental error using the same Hückel equations as those determined in Part 1 in dilute NaCl solutions from (0 to 80) °C. For comparison, also other parametrization (obtained in Part 1 for higher temperatures) was here considered and it applies better to less dilute solutions in the higher temperatures than the model recommended now primarily. Following the success of the new models, we supplement the thermodynamic tables of Part 1 with the relative apparent and partial molar hear capacities for NaCl solutions. We have good reason to believe that the new tables contain the most reliable values available for the heat capacity quantities in dilute NaCl solutions.

Traceable Thermodynamic Quantities for Dilute Aqueous Sodium Chloride Solutions at Temperatures from (0 to 80) °C. Part 1. Activity Coefficient, Osmotic Coefficient, and the Quantities Associated with the Partial Molar Enthalpy

We present fully traceable two-parameter Huckel equations (with parameters B and b1) for the activity coefficient of sodium chloride and for the osmotic coefficient of water in aqueous NaCl solutions at temperatures from (0 to 80) °C. These equations apply within experimental error to all thermodynamic data available for these solutions at least up a molality of 0.2 mol·kg–1. In our previous study (J. Chem. Eng. Data 2016, 61, 286–306), these equations were successfully tested against the literature results of electrochemical, isopiestic, and cryoscopic measurements usually in the temperature range from (0 to 25) °C. There, a constant value was employed for B, whereas a linear model with respect to the temperature was utilized for b1. The linear model was determined from the values of b1 at 0 °C and at 25 °C obtained from freezing-point depression data and from isopiestic and cell-potential difference data, respectively. In the present study, these two b1 values are utilized alongside the constant value o...

Molecular structure of carboxymethyl starch in dilute aqueous sodium chloride solutions

The dilute solution behavior of six carboxymethyl starch (CMS) samples was investigated in aqueous NaCl solutions of different concentration (0.01, 0.05, 0.1, and 0.5 M) by dynamic light scattering (DLS) at 25°C. The values of weight average molar mass, Mw, of the investigated CMS samples were in the range from 9 × 105 to 2.1 × 107 g/mol. Three of the CMS samples were obtained from corn starch and the other three from potato starch. They had different degrees of substitution, DS, ranging from 0.4 to 1.1. The translational diffusion coefficient, Dz, and hydrodynamic radius, Rh, were determined for all CMS samples in aqueous NaCl solutions of different concentrations by the DLS method. The obtained results were treated together with previous results obtained by static light scattering and viscometry, which enabled the calculation of the structure-sensitive parameter, ρ, and the dependence of Rh, radius of gyration, Rg, and viscosity radius, Rη, on molar mass. The calculated values of the ρ parameter were independent of molar mass. The parameter ρ did not change significantly with the variation of the salt concentration in water, its values being in the range from 1.10 to 1.19. The values of exponent νi in the log–log dependence of Rg, Rh, and Rη on Mw were in the range between 0.42 and 0.47; 0.36 and 0.49; 0.42 and 0.44, respectively. These values are characteristic of branched structures of macromolecules.

Ca2+ and Cu2+ Induced Conformational Changes of Sodium Polymethacrylate in Dilute Aqueous Solution

The coil contraction of sodium polymethacrylate in dilute aqueous sodium chloride solution (0.1 N, pH = 9) was monitored by static and dynamic light scattering when the Na+ ions were partly replaced by Ca2+ or Cu2+ ions. The effect was quantified as a function of polyion and bivalent metal ion concentration. The impact of Cu2+ ions on the chain conformation and the solubility of sodium polymethacrylate was observed to be larger than the corresponding effect of Ca2+ ions. This difference was ascribed to complexation of the carboxylate group with bivalent metal cations which is larger for the Cu2+ than for the Ca2+ ion. Even at the largest extent of contraction observed close to the precipitation threshold, the ratio of the radius of gyration and the hydrodynamic radius remained unchanged in contrast to the coil−globule transition observed for neutral polymer systems below the ϑ-temperature.

Prediction of the thermodynamic properties and the phase behavior of binary mixtures in the extended critical region

A new parametric crossover equation of state for pure fluids and binary mixtures, which incorporates the scaling laws asymptotically close to the critical point and is transformed into the regular classical expansion far away from the critical point, is proposed. A comparison is made with the experimental data for pure methane, ethane and n-butane, and for binary mixtures of methane and ethane, and of ethane and n-butane. The equation of state yields a satisfactory representation of the thermodynamic property data in a large range of temperatures and densities. An application for dilute aqueous sodium chloride solutions is also discussed.

Freezing Point Depression of Dilute Aqueous Sodium Chloride Solutions.

Freezing point depressions of dilute aqueous sodium chloride solutions have been computed by means of the best osmotic coefficient equations. In the calculations, the equations of Huckel, Hamer and Pitzer were used for the osmotic coefficients. The experimental freezing point data available in the literature for dilute NaCl solutions can in most cases be predicted within experimental error with Huckel's equation, determined in our laboratory for the temperature of 298.15 K. The measured freezing points can also be calculated very accurately with Hamer's equation determined for the same temperature. The freezing point depressions tabulated in this paper for NaCl solutions can be recommended as reference values. These values are very reliable because they agree accurately with the experimental data and have been calculated by means of Huckel's equation, which, in addition, predicts well almost all existing electrochemical data measured in dilute NaCl solutions at 298.15 K

Purification of monoterpenyl glycosides by gel-permeation and hydrophobic-interaction chromatography on polyacrylamide (Bio-Gel P-2)

Hydrophobic interaction of the aglycone of monoterpenyl glycosides with the polyacrylamide matrix of Bio-Gel P-2 greatly retards the elution of these substances when chromatographed in dilute aqueous sodium chloride. This hydrophobic interaction is eliminated by inclusion of 15% acetonitrile in the eluant, thereby permitting conventional gel-permeation chromatography. Combination of these techniques by sequential chromatography on the same Bio-Gel column, in the hydrophobic interaction mode followed by the gel-permeation mode, provides a simple, yet mild and highly selective procedure for the purification of monoterpenyl glycosides from crude plant extracts. Examination of the chromatographic properties of β- d-glucopyranosides and β- d-galactopyranosides of a number of acyclic, monocyclic, and bicyclic monoterpenols indicates that the extent of hydrophobic interaction is of diagnostic value in determining the nature of the aglycone.

Critical phenomena and thermodynamics of dilute aqueous sodium chloride to 823 K

Semiempirical equations are developed that represent the behavior of dilute solutions of NaCl in water (steam) in the range 723-823 K where ion pairing is extensive. This supplements the equations given earlier for more concentrated solutions. In this temperature range the system NaCl/H(2)O shows critical behavior with two phases below the critical pressure. The equations for the dilute solutions yield critical behavior. Though the equations for concentrated solutions do not yield critical behavior at the critical pressure, only a very small interpolation function is required to connect smoothly the two equations. The ion-pairing equilibrium constants are reported as well as the Gibbs energies of hydration for both ions and ion pairs.

Accurate tracer diffusion coefficients of Na+ and Cl? ions in dilute aqueous sodium chloride solutions measured with the closed capillary method

A simple and absolute closed capillary method is introduced for measuring tracer diffusion coefficients in liquids with both γ- and β-active tracers. In this method a narrow capillary is partially filled with a labelled solution and an unlabelled solution is used to fill the rest of the capillary. The diffusion coefficient is obtained from the time dependence of the monitored activity when the length of the capillary is known. The method has been tested by remeasuring the tracer diffusion coefficients of22NaCl and Na36Cl for solutions covering a wide range of total NaCl concentration. The average precision of the measurements was about 0.3%. The results obtained for Na36Cl tracer diffusion are in good agreement with the data found in literature. The22NaCl tracer diffusion coefficients that were measured in dilute solutions agree well with those obtained using the continuous open-ended capillary method but differ from results for solutions between 0.1 and 1M obtained with the diaphragm cell method.

Hydrophobic interactions and the adherence of Streptococcus sanguis to hydroxylapatite.

Streptococcus sanguis demonstrated a high affinity for hydrocarbon solvents. When aqueous suspensions of the organism were mixed with either hexadecane or toluene, the cells tended to bind to the nonaqueous solvent. Increases in temperature resulted in a greater affinity of cells for hexadecane. Interaction between the cells and hexadecane was also enhanced by dilute aqueous sodium chloride and by low pH (pH less than 5). The results suggest that the cell surface of S. sanguis has hydrophobic properties. Isolated cell walls also tended to partition into the nonaqueous solvent. Amino acid analyses of the walls revealed the presence of several amino acids which possess hydrophobic side chains. It is likely that the hydrophobic amino acids associated with the cell wall contribute to the hydrophobicity of intact S. sanguis. When the adherence of S. sanguis to saliva-coated hydroxylapatite was measured, it was found that hydrophobic bond-disrupting agents, such as the Li+ cation, the SCN- anion, and sodium dodecyl sulfate, were capable of inhibiting the cell-hydroxylapatite union. In addition, it was observed that both urea and tetramethylurea were inhibitors of the adherence, although the latter reagent was the superior inhibitor. The results suggest that the adherence of S. sanguis to saliva-coated smooth surfaces is at least partially dependent on the formation of hydrophobic bonds between the cell and adsorbed salivary proteins. Hydrophobic bonding may contribute to cooperative interactions involving S. sanguis and saliva-coated hydroxylapatite (Nesbitt et al., Infect. Immun. 35:157-165, 1982).

Synthesis of the nonacosapeptide corresponding to mammalian glucagon.

The nonacosapeptide corresponding to the entire amino acid sequence of mammalian glucagon was synthesized via the corresponding sulfoxide, [Met (O)27]-glucagon. For synthesis of the protected nonacosapeptide six subunits were prepared to serve for building blocks. The condensations of subunits were achieved by the HONB-DCC method. Finally, all the protecting groups of the protected peptide were removed by the treatment with methanesulfonic acid-anisole to give [Met (O)27]-glucagon. The sulfoxide was then treated with 3% aqueous thioglycolic acid to give mammalian glucagon. The product was successfully crystallized from dilute aqueous sodium chloride solution. The N to O acyl migration of serine and threonine residues with methanesulfonic acid treatment was studied in detail.

Synthesis of the nonacosapeptide corresponding to the proposed amino acid sequence of turkey glucagon.

The nonacosapeptide corresponding to the proposed amino acid sequence of turkey glucagon was synthesized via the corresponding sulfoxide, [Met (O)27]-turkey glucagon. For the synthesis of the protected nonacosapeptide six peptide fragments were prepared and the condensations of the fragments were achieved by the HONB-DCC method. Finally, all the protecting groups were removed by the treatment with anhydrous hydrogen fluoride-anisole to give [Met (O)27]-turkey glucagon. The sulfoxide was then treated with aqueous thioglycolic acid to give turkey glucagon, which was successfully crystallized from dilute aqueous sodium chloride solution. The biological activity, lipolysis on rat adipocytes, of the synthetic turkey glucagon was as potent as that of mammalian glucagon.

Integral Heats of Dilution, Relative Partial Molal Heat Contents and Heat Capacities of Dilute Aqueous Sodium Chloride Solutions1

Integral Heats of Dilution, Relative Partial Molal Heat Contents and Heat Capacities of Dilute Aqueous Sodium Chloride Solutions¹