Water dielectric constants, dipole moments

We have no measurements of micellar size, since the translation of micelle size into the number of monomers in the micelle is not a simple task and requires assumptions not easily experimentally tested. We are hopeful of extending experimentation in this direction in future research. Table II lists dielectric constants, dipole moments and effective polarities for methanol, 1- and 2-octanol, and water at 25°C. 

Table II. Dielectric Constants, Dipole Moments and Effective Polarities for Methanol, Octanols and Water at 25°C...

For the readers knowing some electrostatics it would be no surprise that charge phosphate groups are located on the outer surface of the double helix. This is because the dielectric constant of water is very large, it is about e 80 (because water molecules have dipole moments, they are polar), while the interior of the double helix is not polar and only weakly... 

Water s high dipole moment also explains the high dielectric constant of water. The mode in which a high dipole moment influences the properties of the water molecule can best be illustrated by comparing H2O to H2S ... 

The dipole moment of a molecule can be obtained from a measurement of the variation with temperature of the dielectric constant of a pure liquid or gaseous substance. In an electric field, as between the electrostatically charged plates of a capacitor, polar molecules tend to orient themselves, each one pointing its positive end toward the negative plate and its negative end toward the positive plate. This orientation of the molecules partially neutralizes the applied field and thus increases the capacity of the capacitor, an effect described by saying that the substance has a dielectric constant greater than unity (80 for liquid water at 20°C). The dipole moments of some simple molecules can also be determined very accurately by microwave spectroscopy. 

Compounds with high dielectric constants such as water, ethanol and acetonitrile, tend to heat readily. Less polar substances like aromatic and aliphatic hydrocarbons or compounds with no net dipole moment (e. g. carbon dioxide, dioxane, and carbon tetrachloride) and highly ordered crystalline materials, are poorly absorbing. 

Both the dielectric constant and dipole moment are comparable to those of water, indicating that HF is a good solvent for inorganic compounds, but many organic compounds are also soluble. In general, the fluorides of +1 metals are much more soluble than those of +2 or +3 metals. At 11 °C, the solubility of NaF is approximately 30 g per 100 g of liquid HF, that of MgF2 is only 0.025 g, and that of A1F3 is 0.002 g. 

There is an extensive chemistry associated with the use of liquid ammonia as a nonaqueous solvent (see Chapter 10). Because it has a dielectric constant of 22 and a dipole moment of 1.46 D, ammonia dissolves many ionic and polar substances. However, reactions are frequently different than in water as a result of differences in solubility. For example, in water the following reaction takes place because of the insolubility of AgCl ... 

According to the Kirkwood theory of polar dielectrics, simple relations (23) between molecular dipole moment vectors and the mean-square total dipole moment of water clusters can be used to compute the static dielectric constant of water. As the normalized mean-square total dipole moment increases towards unity, theory predicts decreases in the static dielectric constant. Since MD results indicate that the mean-square total dipole moment of interfacial water is greater than that for bulk water (48), the static dielectric... 

The concept of dipole moment and its relationship to ion polarizability were discussed in section 1.8. Section 1.19 introduced the concept of dielectric constant of a crystalline solid and its relationship with the polarizability of its constituting ions (see eq. 1.168). The dielectric constant of a liquid solvent such as water represents the capacity of the solvent s molecules to shield the charges of ion... 

Yellowish red oily liquid pungent penetrating odor fumes in air refractive index 1.670 at 20°C density 1.69 g/mL dipole moment 1.60 dielectric constant 4.9 at 22°C freezes at -77°C boils at 137°C reacts with water soluble in ethanol, benzene, ether, chloroform, and carbon tetrachloride dissolves sulfur at ambient temperature (67 g/100 g sulfur chloride). 

Water freezes to ice at 0°C expands by about 10% on freezing boils at 100°C vapor pressure at 0°, 20°, 50°, and 100°C are 4.6, 17.5, 92.5, and 760 torr, respectively dielectric constant 80.2 at 20°C and 76.6 at 30°C dipole moment in benzene at 25°C 1.76 critical temperature 373.99°C critical pressure 217.8 atm critical density 0.322 g/cm viscosity 0.01002 poise at 20°C surface tension 73 dynes/cm at 20°C dissolves ionic substances miscible with mineral acids, alkalies low molecular weight alcohols, aldehydes and ketones forms an azeotrope with several solvents immiscible with nonpolar solvents such as carbon tetrachloride, hexane, chloroform, benzene, toluene, and carbon disulfide. 

Comparison of dipole moments shows only small differences in polarity. From these data, it can be reasoned that micellization in methanol is feasible. Dielectric constants and effective polarities (dipole moment/molar volume) support this premise with more divergent values. It is noted that bis(2-ethyIhexyI) sodium sulfosuccinate forms micelles readily in water and 2-octanol which have the highest and lowest dielectric constants, respectively, but micelles are formed only at low concentrations in methanol whose dielectric constant is intermediate in value. 

Physical properties of the solvent are used to describe polarity scales. These include both bulk properties, such as dielectric constant (relative permittivity), refractive index, latent heat of fusion, and vaporization, and molecular properties, such as dipole moment. A second set of polarity assessments has used measures of the chemical interactions between solvents and convenient reference solutes (see table 3.2). Polarity is a subjective phenomenon. (To a synthetic organic chemist, dichloromethane may be a polar solvent, whereas to an inorganic chemist, who is used to water, liquid ammonia, and concentrated sulfuric acid, dichloromethane has low polarity.)... 

Some other classification schemes are provided in a work by Kolthoff (Kolthoff, 1974). It is according to the polarity and is described by the relative permittivity (dielectric constant) e, the dipole moment p (in 10 ° C.m), and the hydrogen-bond donation ability Another suggested classification (Parker, 1969) stresses the acidity and basicity (relative to water) of the solvents. A third one (Chastrette, 1979), stresses the hydrogen-bonding and electron-pair donation abilities, the polarity, and the extent of self-association. A fourth is a chemical constitution scheme (Riddick et al., 1986). The differences among these schemes are mainly semantic ones and are of no real consequence. Marcus presents these clearly (Marcus, 1998). 

The great solvent power of water, especially for ionic compounds, is due to its dielectric constant. If this were only, say 10, instead of the actual 80, it would mean that water could dissolve only a trace of sodium chloride. This solvent action of water., naturally. plays an important role in geology. In biology, water functions as a means of conveying salts and other substances which circulate in the bodies of animals and plants. It is outside the scope of this book to discuss any further the function of water on this planet, a subject which could fill many volumes. It is important in this context that we now know water molecules to possess a dipole moment and to discover whether perhaps this fact can provide an explanation of the unique properties of water. 

A quantitative theoretical treatment of the dielectric constant, of water and alcohols in terms of hydrogen-bond formation and making use of the gas-molecule values of the electric dipole moment has been published by G. Ostei and J. G. Kirkwood, J. Chem. Phys. 11, 175 (1943). An alternative treatment of water has been made by L. Pauling and P. Pauling (unpublished). 

The formation of solvates is association between unlike species. Solvation is more frequent between substances of high polarity than those of low polarity. This is illustrated by the decrease in the tendency to form solvates with decrease in dipole moment and dielectric constant (shown in parentheses) for N-methylacetamide (3.59 172), to water (1.84 78.4), to ethanol (1.70 24.6) to ammonia (1.48 78.4) to ethanol (1.70 24.6) to ammonia (1.48 J7.8) to me thylcy clohexane (0 2.02) for which few associations are known. 

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