Boric acid, titration

Method 2.13 Determination of 1 to 90% Organic Nitrogen in Polymers. Kjeldahl Digestion - Boric Acid Titration Method... 

METHOD 83 - DETERMINATION OF DOWN TO 50 PPM ORGANIC NITROGEN IN POLYOLEFINS. KJELDAHL DIGESTION - BORIC ACID TITRATION METHOD. 

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. 

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... 

Gas streams can be analy2ed for ammonia by bubbling a measured quantity of the gas through a boric acid solution to absorb the ammonia. The solution is then titrated against sulfuric acid. This analysis is applicable only if other constituents in the gas stream do not react with boric acid. 

Ammonia and ammonium ions in industrial water streams, including waste-water streams, can be determined by either of two methods (ASTM Procedure D1426). In the first, the sample is buffered to a pH of 7.4 and distilled into a solution of boric acid where the ammonia nitrogen is deterrnined colorimetricaHy with Nessler reagents or titrated using standard sulfuric acid. 

The apparent acid strength of boric acid is increased both by strong electrolytes that modify the stmcture and activity of the solvent water and by reagents that form complexes with B(OH) 4 and/or polyborate anions. More than one mechanism may be operative when salts of metal ions are involved. In the presence of excess calcium chloride the strength of boric acid becomes comparable to that of carboxyUc acids, and such solutions maybe titrated using strong base to a sharp phenolphthalein end point. Normally titrations of boric acid are carried out following addition of mannitol or sorbitol, which form stable chelate complexes with B(OH) 4 in a manner typical of polyhydroxy compounds. EquiUbria of the type ... 

For the most part boric acid esters are quantitated by hydrolysis in hot water followed by determination of the amount of boron by the mannitol titration (see Boron compounds, boric oxide, boric acid and borates). Separation of and measuring mixtures of borate esters can be difficult. Any water present causes hydrolysis and in mixtures, as a result of transesterification, it is possible to have a number of borate esters present. For some borate esters, such as triethanolamine borate, hydrolysis is sufftciendy slow that quantitation by hydrolysis and titration cannot be done. In these cases, a sodium carbonate fusion is necessary. 

The sulfide ions in Ln S, LnSF were detenuined after sample s treatment by titrated solution in a week-acid media. Excess iodine was titrated with Na S Oj solution. Fluoride ions in LnF, LnSF were detenuined after sample s treatment by H BO titrated solution. After the removal of BF excess boric acid was converted into the stronger mannitoboric acid, which was titrated potentiometrically with NaOFI solution. 

Boric acid behaves as a weak monoprotic acid with a dissociation constant of 6.4 x 10-10. The pH at the equivalence point in the titration of 0.2M sodium tetraborate with 0.2 M hydrochloric acid is that due to 0.1 M boric acid, i.e. 5.6. Further addition of hydrochloric acid will cause a sharp decrease of pH and any indicator covering the pH range 3.7-5.1 (and slightly beyond this) may be used suitable indicators are bromocresol green, methyl orange, bromophenol blue, and methyl red. 

For work of the highest precision a comparison solution or colour standard may be prepared for detecting the equivalence point. For 0.05 M solutions, this is made by adding 5 drops of methyl red to a solution containing 1.0 g of sodium chloride and 2.2 g of boric acid in 500 mL of water the solution must be boiled to remove any carbon dioxide which may be present in the water. It is assumed that 20 mL of wash water are used in the titration. 

The method may be applied to commercial boric acid, but as this material may contain ammonium salts it is necessary to add a slight excess of sodium carbonate solution and then to boil down to half-bulk to expel ammonia. Any precipitate which separates is filtered off and washed thoroughly, then the filtrate is neutralised to methyl red, and after boiling, mannitol is added, and the solution titrated with standard 0.1M sodium hydroxide solution ... 

Procedure. To determine the purity of a sample of boric acid, weigh accurately about 0.8 g of the acid, transfer quantitatively to a 250 mL graduated flask and make up to the mark. Pipette 25 mL of the solution into a 250 mL conical flask, add an equal volume of distilled water, 2.5-3 g of mannitol or sorbitol, and titrate with standard 0.1 M sodium hydroxide solution using phenolphthalein as indicator. It is advisable to check whether any blank correction must be made dissolve a similar weight of mannitol (sorbitol) in 50 mL of distilled water, add phenolphthalein, and ascertain how much sodium hydroxide solution must be added to produce the characteristic end point colour. 

Procedure. To 100 mL of distilled water, add 5mL of concentrated sulphuric acid, cool and then add 5 g of pure boric acid when this has dissolved cool the mixture in ice. Transfer gradually from a weighing bottle about 0.5 g (accurately weighed) of the sodium peroxide sample (handle with care) to the well-stirred, ice-cold solution. When the addition is complete, transfer the solution to a 250 mL graduated flask, make up to the mark, and then titrate 50 mL portions of the solution with standard 0.02 JVf permanganate solution. 

It may be noted that very weak acids, such as boric acid and phenol, which cannot be titrated potentiometrically in aqueous solution, can be titrated conductimetrically with relative ease. Mixtures of certain acids can be titrated more accurately by conductimetric than by potentiometric (pH) methods. Thus mixtures of hydrochloric acid (or any other strong acid) and acetic (ethanoic) acid (or any other weak acid of comparable strength) can be titrated with a weak base (e.g. aqueous ammonia) or with a strong base (e.g. sodium hydroxide) reasonably satisfactory end points are obtained. 

Other suggested experiments include titration of 0.05M Na2C03 with 0.1M HC1, and of 0.1M boric acid in the presence of 4 g of mannitol with O.lMNaOH. 

A 10 mM ionic strength universal buffer mixture, consisting of Good zwitterio-nic buffers, [174] and other components (but free of phosphate and boric acid), is used in the pION apparatus [116,556], The 5-pKa mixture produces a linear response to the addition of base titrant in the pH 3-10 interval, as indicated in Fig. 7.53. The robotic system uses the universal buffer solution for all applications, automatically adjusting the pH with the addition of a standardized KOH solution. The robotic system uses a built-in titrator to standardize the pH mapping operation. 

Ruzhentseva et al (6 +) converted hydralazine to ammonia by heating with zinc in sulfuric acid, forming 3 moles of ammonia per mole of hydralazine. The mixture was made alkaline and the ammonia was distilled into boric acid solution, which was then titrated. 

The acid in the receiving vessel can be either a dilute (perhaps 0.10 N) standardized solution of a strong acid, such as sulfuric acid, or a solution of boric acid. If it is the former, it is an example of a back titration. If it is the latter, it is an example of an indirect titration. 

The amount of standardized acid needed is proportional to the amount of ammonia that bubbled through. It is an indirect method because the ammonia is determined but not titrated. It is determined indirectly by titration of H2B03. In a direct titration, the analyte would be reacted directly with the titrant, as per the discussion in Section 4.6. The concentration of the boric acid in the receiving vessel does not enter into the calculation and need not be known. Equation (4.40) is used for the calculation. 

A flour sample was analyzed for nitrogen content by the Kjeldahl method. If 0.9819 g of the flour was used, and 35.10 mL of 0.1009 NHC1 was used to titrate the boric acid solution in the receiving flask, what is the percent nitrogen in the sample ... 

Due to the chemical interactions between PVA and boric acid that lead to directly proportionally of the swollen hydrogel shrinking and the boric acid concentration, a sensor for this acid, difficult to determine by classical titration because of its weakness, has been proposed [162],... 

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