Nitrous acid, titration

Ferrous Sulfdte Titration. For deterrnination of nitric acid in mixed acid or for nitrates that are free from interferences, ferrous sulfate titration, the nitrometer method, and Devarda s method give excellent results. The deterrnination of nitric acid and nitrates in mixed acid is based on the oxidation of ferrous sulfate [7720-78-7] by nitric acid and may be subject to interference by other materials that reduce nitric acid or oxidize ferrous sulfate. Small amounts of sodium chloride, potassium bromide, or potassium iodide may be tolerated without serious interference, as can nitrous acid up to 50% of the total amount of nitric acid present. Strong oxidizing agents, eg, chlorates, iodates, and bromates, interfere by oxidizing the standardized ferrous sulfate. 

Fifty cm3 of 1.000 M nitrous acid is titrated with 0.850 M NaOH. What is the pH of the solution... 

Hydrochloric acid and sulphuric acid are widely employed in the preparation of standard solutions of acids. Both of these are commercially available as concentrated solutions concentrated hydrochloric acid is about 10.5- 12M, and concentrated sulphuric acid is about 18M. By suitable dilution, solutions of any desired approximate concentration may be readily prepared. Hydrochloric acid is generally preferred, since most chlorides are soluble in water. Sulphuric acid forms insoluble salts with calcium and barium hydroxides for titration of hot liquids or for determinations which require boiling for some time with excess of acid, standard sulphuric acid is, however, preferable. Nitric acid is rarely employed, because it almost invariably contains a little nitrous acid, which has a destructive action upon many indicators. 

If a solution of a nitrite is titrated in the ordinary way with potassium permanganate, poor results are obtained, because the nitrite solution has first to be acidified with dilute sulphuric acid. Nitrous acid is liberated, which being volatile and unstable, is partially lost. If, however, a measured volume of standard potassium permanganate solution, acidified with dilute sulphuric acid, is treated with the nitrite solution, added from a burette, until the permanganate is just decolorised, results accurate to 0.5-1 per cent may be obtained. This is due to the fact that nitrous acid does not react instantaneously with the permanganate. This method may be used to determine the purity of commercial potassium nitrite. 

Cupferron Nitroso-R-salt 688 Nitrous acid removal of. 514 Nonaqueous titrations 307 indicators for, 284 solvents for. 283... 

As described more fully in Sections 3.1-3.3, with increasing pH the reactive forms of the diazotizing agent are converted into ineffective ones, namely free nitrous acid, HN02, and the nitrite ion, N02. From the discussion of the mechanism of diazotization it will also become apparent why the reaction proceeds better, that is faster, in dilute hydrochloric than in dilute sulfuric acid. With very slow diazotizations for instance, because of high dilution as in nitrite titrations, the use... 

In contrast to the acid, sodium nitrite should not in general be added in excess. Firstly, as far as the ratio of amine to nitrite is concerned, diazotization is practically a quantitative reaction. In consequence, it provides the most important method for determining aromatic amines by titration. Secondly, an excess of nitrous acid exerts a very unfavorable influence on the stability of diazo solutions, as was shown by Gies and Pfeil (1952). Mechanistically the reactions between aromatic diazonium and nitrite ions were investigated more recently by Opgenorth and Rtichardt (1974). They showed that the primary and major reaction is the formation of aryl radicals from the intermediate arenediazonitrite (Ar —N2 —NO2). Details will be discussed in the context of homolytic dediazoniations (Secs. 8.6 and 10.6). 

In the context of the stability of the nitrosoamine intermediate in the diazotization of heteroaromatic amines relative to that in the case of aromatic amines, the reversibility of diazotization has to be considered. To the best of our knowledge the reverse reaction of a diazotization of an aromatic amine has never been observed in acidic solutions. This fact is the basis of the well-known method for the quantitative analysis of aromatic amines by titration with a calibrated solution of sodium nitrite (see Sec. 3.3). With heteroaromatic amines, however, it has been reported several times that, when using amine and sodium nitrite in the stoichiometric ratio 1 1, after completion of the reaction nitrous acid can still be detected with Kl-starch paper,... 

Let s consider a typical titration problem. A 100.0 mL sample of 0.150 M nitrous acid (p/E, = 3.35) was titrated with 0.300 M sodium hydroxide. Determine the pH of the solution after the following quantities of base have been added to the acid solution ... 

O Suggest an indicator that could be used for the titration of potassium hydroxide with nitrous acid. Explain your suggestion. 

A small amount of iodide is included in the titration mixture. At the end-point the first drop of excess of nitrous acid converts iodide to iodine and this is detected using starch indicator. 

Titration with nitrous acid is used in pharmacopoeial assays of the following benzocaine, dapsone, primaquine, procainamide, procaine, sulphacetamide, sulphadoxine, sulphamethizole, sulphapyridine and sulphathiazole. 

Note Methyl Red is partly decolorized by nitrous acid, hence it is advisable to add the indicator towards the end of the titration Calculations for Total Acidity in Terms of HjSO ... 

Titration shows that a 5.0 mb sample of nitrous acid, HNO2, has a molarity of 0.50. If 8.0 mb of mc nesium hydroxide, Mg(OH)2, was added to the acid to accomplish the neutralization, what must the molarity of the base have been ... 

By multiplying the ml s of NO by 1.34, the values in mg s are obtained. Wiggam Goodyear (Ref 2a) stated that values in excess of 6.5mg of NO per lg of a propellant indicate instability Note Instead of using the Schultze-Tiemann method, a simple titration of the above soln(see h) with alkali might suffice. This titration gives the amts of nitric and nitrous acids which form as the result of the reaction ... 

The primary aromatic amines are most readily estimated by means of nitrous acid (see p. 493). Primary or secondary amines, either alone or in presence of tertiary amines, may be estimated by acetylation, since the last do not react. About 1 gm. of the substance or mixture is weighed into a small flask provided with a reflux air condenser, and 5 c.cs. of acetic anhydride added from a pipette having a soda-lime guard tube. In another flask, also provided with a similar condenser, 5 c.cs. acetic anhydride are placed. The two flasks are allowed to stand at room temperature for 30 minutes to 1 hour, after which time 50 c.cs. of water are added to each, and both are placed on the steam bath for an hour in order to convert the remaining acetic anhydride into acetic acid. After cooling, the amount of acetic acid in each flask is titrated with standard sodium hydroxide or standard baryta, using phenolphthalein as indicator. The difference in the two titrations corresponds to the amount of primary or secondary amine present. 

The nitric oxide was determined as usual—by absorption in water and titration. Control experiments on the combustion of the gas at low temperature and of analysis according to Kjeldahl (reduction of nitric and nitrous acids to NH3 by the action of MgAl-alloy in alkaline solution, distillation and absorption of NH3 by acid) convinced us that the gas contained no noticeable traces of sulphur and that the acidity as ordinarily determined depends on nitric and nitrous acids. 

Sodium nitrite, NaN02, is frequently added to processed meats as a preservative. The amount of nitrite ion in a sample can be determined by acidifying to form nitrous acid (HN02), letting the nitrous acid react with an excess of iodide ion, and then titrating the... 

The nature of the active site in beta-amylase is not unambiguously known for enzymes from different sources. Early experiments on purified barley and on malted barley first indicated, from studies of the modification of the enzyme with nitrous acid and ketene, that free tyrosine and sulfhydryl groups are essential for activity, whereas free a-amino groups are not. The importance of the sulfhydryl groups was emphasized by the partial recovery of activity of the modified or oxidized enzyme (that is, treated with nitrous acid, iodine, phenyl mercuribenzoate, ferricyanide, and cupric ions) when it was treated with hydrogen sulfide or cysteine. Barley feeto-amylase (not highly purified) has been reported to contain 12—15 sulfhydryl groups per molecule by titration with p-chloromercuribenzoate, and the loss of free sulfhydryl content by treatment with L-ascorbic acid in the presence of cupric ions was found to be directly related to the loss of activity. 

Philpot and Small (1938) present evidence, though not from titration data, that nitrous acid attacks the tyrosine residues of pepsin to yield a diazo derivative of the protein. 

Standardization. K 50-nil aliquot of the silver nitrate solution is added to 5 ml of concentrated nitric acid (free from nitrous acid) and 2 ml of a saturated solution of ferric alum. The silver nitrate solution is titrated with the ammonium thiocyanate solution until a fleeting reddish endpoint is reached. The strength of the ammonium thiocyanate solution is calculated from the titer. 

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