Hydroxyl value, definition

Specification sheets will often give the equivalent weight of the polyol in terms of the hydroxyl number ("OH" value). The hydroxyl number is defined as "the number of milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl content of 1.0 grams of polyol." Manipulation of this definition gives the follow equation ... 

Senchenya et al. (96) have treated the adsorption of ethanol on a structural hydroxyl group (Fig. 14) using a CTP scheme and the CNDO/BW method. The separation of a molecule and cluster with respect to the z axis was optimized, the optimal values being r = 1.19 A and R = 1.28 A The adsorption energy was 23.2 kcal/mol, which was close to the experimental value (97). Note that this was essentially the two-point adsorption involving both acid and base sites. This case is quite similar to the above propylene adsorption (90). There is also no definite trend toward proton transfer from the hydroxyl group of a zeolite to the alcohol molecule. The carbocation state is also predicted to be activated. This, in turn, increases relative efficiency of the synchronous mechanism (with the same recommendation for its experimental examination). The estimation (96) of the energetics of the intermediate structures of the synchronous mechanism showed that such a mechanism is quite realistic. 

Many properties of electrolytic solutions are additive functions of the properties of the respective ions this is at once evident from the fact that the chemical properties of a salt solution are those of its constituent ions. For example, potassium chloride in solution has no chemical reactions which are characteristic of the compound itself, but only those of potassium and chloride ions. These properties are possessed equally by almost all potassium salts and all chlorides, respectively. Similarly, the characteristic chemical properties of acids and alkalis, in aqueous solution, are those of hydrogen and hydroxyl ions, respectively. Certain physical properties of electrolytes are also additive in nature the most outstanding example is the electrical conductance at infinite dilution. It will be seen in Chap. II that conductance values can be ascribed to all ions, and the appropriate conductance of any electrolyte is equal to the sum of the values for the individual ions. The densities of electrolytic solutions have also been found to be additive functions of the properties of the constituent ions. The catalytic effects of various acids and bases, and of mixtures with their salts, can be accounted for by associating a definite catalytic coefl5.cient with each type of ion since undissociated molecules often have appreciable catalytic properties due allowance must be made for their contribution. 

Approximate Methods for Bases.—The procedures described for determining the dissociation constants of acids can also be applied, in principle, to bases analogous equations are applicable except that hydroxyl ions replace hydrogen ions, and vice versa, in all the expressions. Since the value of the product of an and ooir is known to have a definite value at every temperature (cf. Table LXI), it is possible to derive ooh" from obtained experimentally. 

Determination of Ionic Product Conductance Method.—Since it contains a certain proportion of hydrogen and hydroxyl ions, even perfectly pure water may be expected to have a definite conductance the purest water hitherto reported was obtained by Kohlrausch and Heyd-weiller after forty-eight distillations under reduced pressure. The specific conductance of this water was found to be 0.043 X 10 ohm cm. at 18 , but it was believed that this still contained some impurity and the conductance of a 1 cm. cube of perfectly pure water was estimated to be 0.0384 X 10 ohm i cm. at 18 . The equivalent conductances of hydrogen and hydroxyl ions at the very small concentrations existing in pure water may be taken as equal to the accepted values at infinite dilution these are 315.2 and 173.8 ohms cm. respectively, at 18 , and hence the total conductance of 1 equiv. of hydrogen and 1 equiv. of hydroxyl ions, at infinite dilution, should be 489.0 ohms cm. It follows, therefore, that 1 cc. of water contains... 

Since the point of bubble evolution represents a more or less indefinite rate of discharge of hydrogen and hydroxyl ions, recent work on overvoltage has been devoted almost exclusively to measurements made at definite c.d. s it is then possible to obtain a more precise comparison of the potentials, in excess of the reversible value, which must be applied to different electrodes in order to obtain the same rate of ionic discharge in each case. The details of the methods of measurement and a discussion of the results will be given after the general problem of the mechanism of electrode processes has been considered. 

Where (Pfi is a universal constant having the value of 0.60, 0f% = 1 — Ofi, VfilVfii is the ratio of the hole volume to the vibrational volume (Schwingungsvolumen) of a repeat unit, and is the energy needed for the formation of a mole of holes. Since this theory was derived for the case where the end groups do not differ appreciably from the repeat units, and this is definitely not the case for the -0 Na terminated material, it was applied only to the hydroxyl terminated polymer. From a graph of IfTg vs. 1/P , shown in Fig. 2, the slope and... 

The classical theory of catalysis supposed that the hydrogen and hydroxyl ions were the only effective catalysts in solutions of acids and bases. In a few instances early attempts were made to remedy some of the discrepancies encountered by attributing some catalytic power to undissociated acid molecules, but these attempts were mostly based on incorrect values for degrees of dissociation, and they did not take into account the possibility of primary or secondary salt effects. However, later work has shown definitely that species other than hydrogen and hydroxyl ions often can exert a catalytic effect, and the development of these ideas was closely linked with a closer understanding of the nature of the hydrogen ion in solution, and with the clarification of acid-base definitions (cf. Bell, 11). 

With this definition p0H- was calculated from the hydroxyl mobility data computed as above. From the data of Tosteson (20), assuming cell water is 72% of cell volume (27), pCr is about 10"4 cm/sec and Wcr is 4.0 X 10"12 cm/sec (mv/cm)"1, the value that was used in the computations. 

Hazel et al. were the first to study the strong interaction between metal ions, specificaUy Fe, and silicate species [69]. Later, when studying corrosion inhibition of zinc by silica. Hazel et al. [70] measured the interaction of Zn ion and silicates and observed slight, but definite, pH value shifts in pH titration inflection points. They suggested that hydroxyl ion was being adsorbed, or occluded, by the amorphous sihceous precipitates. Chemisorption of sihca at a zinc hydroxide surface appeared to occur independent of the surface charge or the exact chemical composition of the surface. Falcone [71] measured the activities of Ca, Mg" and Cu" in the presence of soluble silica. Polymerized sihcate anions also shifted the pMe vs. pH curves to lower pH values... 

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