Ionization of boric acid

In concentrated solutions boric acid forms a complex mixture of polyborate ions. In such solutions data obtained from titrations are complicated by the presence of these complex ions. Aqueous boric acid solutions below 0.2M seem to have negligible amounts of polyborate ions (14). Much of the early data reported in the literature was collected using more concentrated solutions (3). Thus, the ionization of boric acid can be described by the following equation ... 

Until recently, very little had been reported on the important area of metal borate complexation in aqueous solution. The effect of salts on the ionization of boric acid (358, 375) has been mentioned above, and subsequent research suggests that complexation of borate with, for example, calcium ions can account for the enhanced acidity of H O Literature on cationic complexes of boron was reviewed in 1970 (376). 

Ward G.K. and Millero F.J. (1974) The effect of pressure on the ionization of boric acid in aqueous solutions from molal volume data. J. Sol. Chem. 3, 417-430. 

Write net ionic equations for the three ionizations of boric acid (H3BO3) in water. Include H2O in the three equations. Identify the conjugate acid-base pairs. 

Using the data in Figure 17.15, what is the heat of ionization of boric acid ... 

The ionization of boric acid is enhanced in solutions containing carbohydrates (143). This effect is variable, apparently depending upon the individual complexing ability of the sugar. Khym and Zill (144) have used this effect to separate sugars by removing their borate complexes from ion-exchange resins in columns by differential elution with acid developers... 

Boric acid, B(OH)3, is used as a mild antiseptic. What is the pH of a 0.021 M aqueous solution of boric acid What is the degree of ionization of boric acid in this solution The hy-dronium ion arises principally from the reaction... 

C17-0069. Determine the percent ionization of a solution of boric acid that is 75 mM (see AppendixE for K values). 

Buffers contain mixtures of weak acids and their salts (i.e., the conjugate bases of acids), or mixtures of weak bases and their conjugate acids. Typical buffer systems used in pharmaceutical dosage forms include mixtures of boric acid and sodium borate, acetic acid and sodium acetate, and sodium acid phosphate and disodium phosphate. The reason for the buffering action of a weak acid, HA (e.g., acetic acid) and its ionized salt, A" (e.g., sodium acetate) is that A" ions from the salt combine with the added hydrogen ions, removing them from solution as undissociated weak acid. 

Other studies into the apparent ionization constant of boric acid and interpretation of data are given by Sprague (392). Of greater relevance... 

Boron rejection membranes exhibit up to 90+% rejection of boron, while standard membranes reject about 50-70%.(20, 29) These membranes are typically used for seawater applications where boron removal is a concern. Boron is difficult to remove with membranes because boron, which exists as boric acid, is not ionized a typical seawater pH, 7.0 - 8.0, whereas the pKa of boric acid is 9.14 - 9.25.20... 

The ammonia can be distilled into an excess of standard sulfuric acid, and the excess determined by back titration. Preferably, the distilled ammonia can be absorbed into a solution of boric acid or other weak acid. Direct titration of the boric acid distillate with standard acid, using bromophenol blue, with a blank determination gives excellent results. As a routine method for determining traces of nitrogen, Milner and Zahner distilled the ammonia into a dilute boric acid solution. Urban suggested an aqueous solution of p-hydroxybenzoic acid (ionization constant 2.9 X 10 ) as an ammonia-absorbing solution. 

G. Manov, N. DeLolUs and S. Acree, Ionization constant of boric acid and the pH of certain borax-chloride buffer solutions from 0° to 60° C, /. Res. Natl. Bur. Stand., 1944,33,287-306. 

K is the apparent ionization constant of boric acid in presence of different ligand concentrations and has to be determined. The coordination number can be obtained directly from the slope of the curve p (K — Ki) against — log Cn. The resulting values of are apparently independent of the ionic strength. Fig. 8 shows an example of the concentration dependence of the apparent ionization constant of boric acid. 

Cubic boron nitride films have also been prepared by activated reactive evaporation of boric acid in an NH3 plasma formed between a hot filament and an anode [119 to 121]. Other reports on ionized deposition of BN layers [122,123] and on p-BN deposited by sputtering in an NH3 or N2/Ar atmosphere [124, 125] show that the formation of the different BN phases in the resultant coatings depends critically on the conditions of the process. About the effects of the total gas pressure and the type of sputtering gas on the stresses of thin p-BN films, see [138]. 

The presence of B(OH>3 increases the rate of hydrolysis of ionized phenyl salicylate (PS ) by nearly 10 -fold compared to the rate of hydrolysis of phenyl benzoate under essentially similar conditions (Equation 2.34). However, the hydrolysis of PS crtn also occur with measurable rate in the absence of B(OH)3. Nearly 10 -fold rate enhancement due to the presence of boric acid is attributed to the boric-acid-induced intramolecular reaction involving transition state TS,6. An alternative and kinetically indistinguishable mechanism involving transition state TSiy has been ruled out on the basis of the absence of enhanced nucleophilic reactivity of tertiary and secondary amines toward phenyl salicylate in the presence of borate buffer. 

OH ion from the self-ionization of water, forming the complex ion [B(OH)4]. Thus, the source of the H3O in B(OH)3(aq) is the water itself. This ionization scheme, together with the fact that B(OH)3 is a monoprotic, not fnprotic, acid suggests that the best formula of boric acid is B(OH)3, not H3BO3. 

Anions of weak acids can be problematic for detection in suppressed IEC because weak ionization results in low conductivity and poor sensitivity. Converting such acids back to the sodium salt form may overcome this limitation. Caliamanis et al. have described the use of a second micromembrane suppressor to do this, and have applied the approach to the boric acid/sodium borate system, using sodium salt solutions of EDTA.88 Varying the pH and EDTA concentration allowed optimal detection. Another approach for analysis of weak acids is indirect suppressed conductivity IEC, which chemically separates high- and low-conductance analytes. This technique has potential for detection of weak mono- and dianions as well as amino acids.89 As an alternative to conductivity detection, ultraviolet and fluorescence derivatization reagents have been explored 90 this approach offers a means of enhancing sensitivity (typically into the low femtomoles range) as well as selectivity. 

Kryukov, P.A. Starostina, L.I. Tarasenko, S.Ya Pavlyuk, L.A. Smolyakok, B.S. Larionov, E.G. "Ionization Constants of Carbonic Acid, Hydrogen Sulfide, boric Acid, and Sulfuric Acid at High Temperatures," Mezhdunar. Geokhim., Koagr. (Dokl.) 1st, 1971, 186-98 C.A, 1974, 84 (69193). 

For all the other halides, Eh-pH conditions have no influence. Boron occurs in water mainly as boric acid H3BO3 and its progressive ionization products at increasing pH. Redox conditions do not affect the speciation state of boron. 

The parent acid, H3B03, functions as a weak acid in aqueous solution, possessing an ionization constant of about 6 x 10-, at 25°C in dilute solution. As its concentration increases, the ionization constant increases markedly. Kolthoff (220) investigated this effect by electrical conductivity and emf measurements, obtaining values of 4.6 x 1010 and 408 x 10 1 for boric acid concentrations of 0.1 M and 0.75 M respectively at 18°C. These results were attributed to the formation of tetraboric acid. 

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