Boric acidity

Boron trichloride, BCI3. Colourless mobile liquid, m.p. — 107°C, b.p. 12-5°C. Obtained directly from the elements or by heating B2O3 with pels in a sealed tube. The product may be purified by distillation in vacuo. It is extremely readily hydrolysed by water to boric acid. TetrachJoroborates containing the BCJ4 " ion are prepared by addition of BCI3 to metal chlorides. 

Boron III) oxide, B2O3, is obtained by ignition of boric acid. Combines with water to reform B(0H)3. The fused oxide dissolves metal oxides to give borates. 

Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

Strong oxidising acids, for example hot concentrated sulphuric acid and nitric acid, attack finely divided boron to give boric acid H3CO3. The metallic elements behave much as expected, the metal being oxidised whilst the acid is reduced. Bulk aluminium, however, is rendered passive by both dilute and concentrated nitric acid and no action occurs the passivity is due to the formation of an impervious oxide layer. Finely divided aluminium does dissolve slowly when heated in concentrated nitric acid. 

Boron trioxide, B2O3 is the anhydride of boric acid, H3BO3 and can be prepared by heating the acid ... 

Boron trioxide is not particularly soluble in water but it slowly dissolves to form both dioxo(HB02)(meta) and trioxo(H3B03) (ortho) boric acids. It is a dimorphous oxide and exists as either a glassy or a crystalline solid. Boron trioxide is an acidic oxide and combines with metal oxides and hydroxides to form borates, some of which have characteristic colours—a fact utilised in analysis as the "borax bead test , cf alumina p. 150. Boric acid. H3BO3. properly called trioxoboric acid, may be prepared by adding excess hydrochloric or sulphuric acid to a hot saturated solution of borax, sodium heptaoxotetraborate, Na2B407, when the only moderately soluble boric acid separates as white flaky crystals on cooling. Boric acid is a very weak monobasic acid it is, in fact, a Lewis acid since its acidity is due to an initial acceptance of a lone pair of electrons from water rather than direct proton donation as in the case of Lowry-Bronsted acids, i.e. 

In the presence of glycerol or mannitol (polyhydroxo compounds) boric acid behaves as a much stronger acid the reaction can be represented as ... 

Titration. The solution of ammonia absorbed in saturated boric acid may now be titrated as an alkali directly with 0 025 A.HCl (best obtained by dilution of commercially available standard A.HCl in a graduated flask). Three drops of indicator (mixed methyl-red/methyl-ene-blue being most satisfactory) are added to the liquid in the receiver and the 0 025 A.HCl run in from an accurate burette. 

Alkyl borates. By heating boric acid with excess of the alcohol the water formed in the reaction is removed by fractional distillation as an azeo tropic mixture with the alcohoi, for example ... 

This reaction is due to the combination of two da hydroxyl groups of the compound with the boric acid to form a much stronger monobasic acid ... 

If it is desired to employ fluoboric acid HBF4, it can be prepared by adding 100 g. of A.R. boric acid in small proportions to 325 g. of A.R. hydrofluoric acid (40 p>er cent. HF) cooled in ice the hydrofluoric acid is contained in a Bakelite beaker, a beaker coated with wax or in a lead vessel. A simple container may also be prepared by cutting of the neck of the wax bottle (in which the hydrofluoric acid is supplied) with a large e.g., a butcher s ) knife which has been slightly warmed. One-third of the above solution should be employed in the preparation. Handle unth great care. 

The fluoboric acid may be prepared by adding 92 g. of A.R. boric acid slowly and with constant stirring to 250 g. of hydrofluoric acid (40-48 per cent.) in a copjier, lead or a waxed-lined beaker. A lead rod may be used for stirring. All operations should be carried out in a fume cupboard. 

Caustic alkali in the eye. Proceed as for acid in the eye, but wash with 1 per cent, boric acid solution in place of bicarbonate solution. 

Boric acid is also an important boron compound with major markets in textile products. Use of borax as a mild antiseptic is minor in terms of dollars and tons. Boron compounds are also extensively used in the manufacture of borosilicate glasses. Other boron compounds show promise in treating arthritis. 

With sodium hydroxide as the base boron of the alkylborane is converted to the water soluble and easily removed sodium salt of boric acid... 

H3B03 orthoboric acid (or boric acid) H4P2O3 peroxodiphosphoric acid... 

X mL of 0.2M NaOH Added to 100 mL of Stock Solution (0.04M Acetic Acid, 0.04M H3PO4, and 0.04M Boric Acid)... 

Another type of demasking involves formation of new complexes or other compounds that are more stable than the masked species. For example, boric acid is used to demask fluoride complexes of tin(IV) and molybdenum(VI). Formaldehyde is often used to remove the masking action of cyanide ions by converting the masking agent to a nonreacting species through the reaction ... 

Boric acid F, glycol, mannitol, tartrate, and other hydroxy acids... 

Turmeric paper (gives a rose-brown coloration with boric acid) wash tbe ground root of turmeric with water and discard tbe washings. Digest with alcohol and filter, using the clear filtrate to impregnate white, unsized paper, which is then dried. 

Alkali metals Moisture, acetylene, metal halides, ammonium salts, oxygen and oxidizing agents, halogens, carbon tetrachloride, carbon, carbon dioxide, carbon disul-flde, chloroform, chlorinated hydrocarbons, ethylene oxide, boric acid, sulfur, tellurium... 

Although not commonly used, thermometric titrations have one distinct advantage over methods based on the direct or indirect monitoring of plT. As discussed earlier, visual indicators and potentiometric titration curves are limited by the magnitude of the relevant equilibrium constants. For example, the titration of boric acid, ITaBOa, for which is 5.8 X 10 °, yields a poorly defined equivalence point (Figure 9.15a). The enthalpy of neutralization for boric acid with NaOlT, however, is only 23% less than that for a strong acid (-42.7 kj/mol... 

In this experiment phosphate is determined by singlecolumn, or nonsuppressed, ion chromatography using an anionic column and a conductivity detector. The mobile phase is a mixture of n-butanol, acetonitrile, and water (containing sodium gluconate, boric acid, and sodium tetraborate). 

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