Dipole moment of water

The calculated magnitude of the dipole moment of water (2 39 D) is displayed at the bottom of the screen The calculated direction is indicated by a yellow arrow... 

Figure 4 shows the measured angle of 105° between the hydrogens and the direction of the dipole moment. The measured dipole moment of water is 1.844 debye (a debye unit is 3.336 x 10 ° C m). The dipole moment of water is responsible for its distinctive properties in the Hquid state. The O—H bond length within the H2O molecule is 0.96 x 10 ° m. Dipole—dipole interaction between two water molecules forms a hydrogen bond, which is electrostatic in nature. The lower part of Figure 4 (not to the same scale) shows the measured H-bond distance of 2.76 x 10 ° m or 0.276 nm. 

The temperature dependence of the effective charges and dipole moment of water... 

The dipole moment p. is a molecular property defined as the product of charge (usually just a fraction of the electronic change, of course) and distance between the centers of positive and negative charge in the molecule. The dipole moment is usually expressed in debyes (D), where 1 D = 1(T esu in SI units 1 D = 3.3356 X 10 ° C-m. so, for example, the dipole moment of water is 1.84 D or 6.14 in units of 10 C-m. Again a rough correspondence is seen between this property of a molecule and its polarity, though e and p. are not precisely correlated. 

Freitag and John [96] studied rapid separation of stabilisers from plastics. Fairly quantitative extraction (>90% of the expected content) of stabilisers from a powdered polymer was achieved by MAE within 3 to 6 min, as compared to 16 h of Soxhlet extraction for the same recovery. MAE and Soxhlet extraction have also been compared in the analysis of cyclic trimer in PET [113]. On the other hand, Ganzler et al. [128] compared the extraction yields for various types of compounds from nonpolymeric matrices for microwave irradiation with those obtained by the traditional Soxhlet or shake-flask extraction methods. Microwave extraction was more effective than the conventional methods, in particular in the case of polar compounds. As expected, the efficiency of the former is high especially when the extraction solvents contain water. With the high dipole moment of water, microwave heating is more... 

Remarkable data on primary hydration shells are obtained in non-aqueous solvents containing a definite amount of water. Thus, nitrobenzene saturated with water contains about 0.2 m H20. Because of much higher dipole moment of water than of nitrobenzene, the ions will be preferentially solvated by water. Under these conditions the following values of hydration numbers were obtained Li+ 6.5, H+ 5.5, Ag+ 4.4, Na+ 3.9, K+ 1.5, Tl+ 1.0, Rb+ 0.8, Cs+0.5, tetraethylammonium ion 0.0, CIO4 0.4, NO3 1.4 and tetraphenylborate anion 0.0 (assumption). 

Figure 2.5 Bond moments and the resulting dipole moments of water and ammonia.

A fourth solvent structural effect refers to the average properties of solvent molecules near the solute. These solvent molecules may have different bond lengths, bond angles, dipole moments, and polarizabilities than do bulk solvent molecules. For example, Wahlqvist [132] found a decrease in the magnitude of the dipole moment of water molecules near a hydrophobic wall from 2.8 D (in their model) to 2.55 D, and van Belle et al. [29] found a drop from 2.8 D to 2.6 D for first-hydration-shell water molecules around a methane molecule. 

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... 

An exception among organic molecules is the adsorption of thiourea since that gives no maximum on the AG° vs. plot. It was suggested " that such atypical behavior can be expected for any neutral molecule that has the normal to the surface component of the dipole moment sufficiently positive compared with the resulting dipole moment of n displaced water molecules. In the case of a TU molecule oriented with the sulfur atom toward the metal surface, the ratio of /iA// is approximately equal to 2.5 D. This value is greater than the dipole moment of water, thus fulfilling the condition of atypical behavior. The anomalous behavior of thiourea is probably due to the fact that only a few solute molecules satisfy this condition. 

The plots of AG° vs. for differentratios, calculated from the model proposed in Refs. 148, 151, and 152 are presented in Fig.lO. The calculation was made for n = 2, the area occupied by one water molecule equal to 0.09 nm, and for other double-layer parameters that best fit the experimental data on differential capacity of the Hg/water interface. As follows from these plots, no tZmax of adsorption can be reached if the Hfj/n ratio is greater than the dipole moment of water (1.84 D). 

As a very simple example, consider the dipole moment of water. In the gas phase, this dipole moment is 1.85 D (Demaison, Hiimer, and Tiemann 1982). What about water in liquid water A zerofli order approach to answering this problem would be to create a molecular mechanics force held defining the water molecule (a sizable number exist) that gives the correct dipole moment for the isolated, gas-phase molecule at its equilibrium... 

It might at first sight be thought that, since the dipole moment of water is larger than that of ammonia, the hydrates would be more stable, which is certainly true when the field of the ions is weak and polarization consequently has little effect. The energy of an ion with... 

In eq 19, the field is calculated by assuming that the water molecules are organized in icelike layers, jn, being the average dipole moment of water in layer i and C0 and Ci being interaction coefficients given by6... 

Phenomenological evaluation [85,86] using atomic and molecular polarizabilities and the permanent dipole moment of water suggests that under the condition of the experiment, which involve water at high rotational temperature, the long range attraction is accounted for more than 90% by dispersion forces, while induction contributions play a minor role. 

Size and Dipole Moment of Water Molecules in Solution... 

The dipole moment of water in the gas phase is well known as 1.87 D but is 2.42 D in water at 298 K. The reason for the difference is that in liquid water there is electrostatic pull on a given water molecule from the surrounding ones, and this lengthens the distance in the dipoles (Fig. 2.7). 

Conway and Soloman corrected Halliwell and Nyburg s (1%3) value for the numerical value of the dipole moment of water and got -1117 kJ mol". Then, Lister, Nyburg, and Doyntz reattacked the calculation using a different series of ions of the same size. They got -1096 kJ mol . ... 

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