Free mineral acidity

The exchange resins 6nd application in (i) the purification of water (cation-exchange resin to remove salts, followed by anion-exchange resin to remove free mineral acids and carbonic acid), (ii) removal of inorganic impurities from organic substances, (iii) in the partial separation of amino acids, and (iv) as catalysts in organic reactions (e.g., esterification. Section 111,102, and cyanoethylation. Section VI,22). 

Free mineral acidity H2SO4, HCl, and other acids, expressed as CaCOj. Causes rapid corrosion and deterioration of surfaces. 

Weakly basic anion resins derive their functionality from primary (R-NH), secondary (R-NHR ), tertiary (R-N-R 2), and sometimes quaternary amine groups. The weakly basic resin readily absorbs such free mineral acids as hydrochloric and sulfuric, and the reactions may be represented according to the following ... 

Free mineral acids HCI H, SO4 Corrosion Any process usnig alkalines to neurralizc... 

Notes. (1) If in a similar determination, free mineral acid is present, a few drops of dilute sodium carbonate solution must be added until a faint permanent precipitate remains, and this is removed by means of a drop or two of acetic acid. The potassium iodide is then added and the titration continued. For accurate results, the solution should have a pH of 4-5.5. 

The precipitate is soluble in free mineral acids (even as little as is liberated by reaction in neutral solution), in solutions containing more than 50 per cent of ethanol by volume, in hot water (0.6 mg per 100 mL), and in concentrated ammoniacal solutions of cobalt salts, but is insoluble in dilute ammonia solution, in solutions of ammonium salts, and in dilute acetic (ethanoic) acid-sodium acetate solutions. Large amounts of aqueous ammonia and of cobalt, zinc, or copper retard the precipitation extra reagent must be added, for these elements consume dimethylglyoxime to form various soluble compounds. Better results are obtained in the presence of cobalt, manganese, or zinc by adding sodium or ammonium acetate to precipitate the complex iron(III), aluminium, and chromium(III) must, however, be absent. 

Although Hammett convincingly explained the nitrosation of aliphatic amines and the diazotization of aniline under the conditions employed by Schmid and others, one unsatisfactory point remained namely the second-order kinetic equation obtained by Hantzsch and the workers who followed him for diazotization in a more weakly acidic medium. Comparison of experimental details shows that at concentrations of free mineral acid below 0.05 m the reaction is apparently second-order, but it becomes third-order at higher concentrations of acid. 

For preparative diazotisations it is important to use a sufficient excess of acid and to keep the temperature down. Two moles of acid are required for each mole of amine, one for salt formation and one for liberating the nitrous acid from the nitrite. As a rule 2-5-3-0 moles are used. The excess is required to prevent condensation of the diazonium salt with unchanged base to diazoamino-compound such condensations take place in a faintly acid medium. The test for unchanged amine, accordingly, consists in buffering the free mineral acid with sodium acetate, and so providing a solution faintly acid with acetic acid, under which conditions the diazoamino-compound is formed. The latter is decomposed by mineral acids into diazonium salt and amine salt, e.g. 

Huber s reagent analy chem Aqueous solution of ammonium molybdate and potassium ferrocyanide used as a reagent to detect free mineral acid. hyu-barz re,a- 3nt ... 

The reaction of aminoguanidine with sodium nitrite under neutral conditions yields tetra-zolylguanyltetrazene hydrate (85), a primary explosive commonly known as tetrazene. Tetrazene (85) is only formed in the absence of free mineral acid and so a common method for its preparation treats the bicarbonate salt of aminoguanidine (84) with one equivalent of acetic acid followed by addition of aqueous sodium nitrite. " Tetrazene (85) is decomposed by aqueous alkali to form triazonitrosoaminoguanidine (86) which is isolated as the cuprate salt (87) on addition of copper acetate to the reaction mixture. Acidification of the copper salt (87) with mineral acid leads to the formation of 5-azidotetrazole (88) (CHN7 = 88 % N).55 56... 

If a b increases continuously, the wine contains no free acid, but if it first diminishes and only increases after a certain amount of alkali has been added, the presence of free mineral acid may be concluded. It is convenient to represent graphically the relation between the values of b and of the amounts of alkali added,... 

Total alkalinity of the ash. This alkalinity, expressed in c.c. of N-alkali per litre is, on the average, ten times the number of grams of ash per litre. A low value of the alkalinity of the ash may indicate some treatment of the wine such as plastering or addition of phosphate of free mineral acid, resulting in decomposition Or precipitation especially of the potassium bitartrate, On which the alkalinity of the ash largely depends. 

Detection of Free Mineral Acids.—This may be effected by one of the following methods ... 

The method is based on the fact that slightly dissociated acids, such as acetic, tartaric, etc., do not exhibit their acidity towards rr ethyl orange in presence of alcohol. If, then, a definite quantity of alkali is added to a genuine vinegar and the added alkali then neutralised in presence of methyl orange by means of an aqueous-alcoholic solution of sulphuric acid, the amount of the latter will correspond exactly with that of the alkali, since the acetic add liberated from the acetate formed does not react with the indicator. If, however, a vinegar contains free mineral acid, the amount of sulphuric acid required will be diminished in accordance with the quantity of the alkali united with the free mineral acid the amount of the latter will thus correspond with the difference between the alkali added and the sulphuric acid necessary for its neutralisation. 

Cooling systems where the operational pH is normally within the range of 6.5 to 9.5 are, generally, not affected by slight changes in pH, although if the pH should drop below 4.3 to 4.0, this will be accompanied by a dramatic increase in corrosion rate due to free mineral acidity. 

Acid leaks result in the deactivation of some chemical treatment programs, for example, P-PO4 is hydrolyzed to O-PO4, and chromate (in the presence of ferrous ions) is reduced to trivalent chromium. Also, depassivation of the inhibitor film and corrosion occurs. The correct action is to first stop the leak, then to increase the pH by bleeding off the low pH water and making up, to the maximum extent of the system. If the leak is so severe that the pH drops below 4.3, and free mineral acidity (FMA) occurs, soda ash should be used to restore the pH to 4.3 to 4.5, then discontinued. Caustic soda should not be added, as this action will almost certainly result in heavy fouling from precipitated ferric hydroxide. Dispersants or antifoulants may be required. When the system is stabilized, it should be repassivated and the reason for the acid leak resolved (faulty pH meter ). 

Precipitation is incomplete owing to the free mineral acid produced. If the hydrogen ions, arising from the complete ionization of the mineral acid, are removed by the addition of the salt of a weak acid, such as ammonium or sodium acetate, precipitation is almost complete. This is the basis of one of the methods for the removal of phosphates, which interfere with the precipitation of Group IIIA metals, in qualitative analysis. 

Sulfonated amines are dissolved as their alkali salts in water, and acetate solution, equivalent to the free mineral acid in the diazo solution plus that formed in the coupling reaction, is added. The diazo solution is added to the coupler solution with stirring. If necessary, the mixture is partially or completely neutralized with soda to accelerate the coupling. 

The reduction of m-nitrobenzenesulfonic acid is carried out by the method given for preparing aniline (page 75), except that the iron need not be etched since the free mineral acid in the press cake is sufficient to start the reaction. In an iron or copper reduction beaker of about 2-liter capacity are placed 250 grams of finely pulverized cast iron and 1 liter of water. This mixture is heated to boiling... 

In the preparation of diamine green B, we have seen how H acid, in mineral acid solution, couples very easily with p-nitroaniline to form a monoazo dye in which the azo group enters the position ortho to the amino group. Benzidine, however, couples appreciably less rapidly, and it is necessary to neutralize the free mineral acid that is formed. Contrary to the statements in the patent literature, it is not possible to carry out this reaction in acetic acid solution, because H acid, in the presence of sodium acetate, couples immediately in the position ortho to the hydroxyl group. These facts have given rise to many patent suits, all of which, however, have been decided in favor of the holders of the mineral acid coupling patents. 

Wet Tests.—The presence of iron in solution may readily be detected by a considerable number of sensitive reactions. Thus ferrous iron gives a green precipitate of ferrous hydroxide upon addition of excess of ammonium hydroxide. With potassium ferricyanide and a trace of acid, a deep blue precipitate—Turnbull s blue—is obtained. With potassium ferrocyanide a white precipitate is obtained in the entire absence of any ferric salt. Ferric iron, on the other hand, is usually characterised by its deep yellow or brown colour. Addition of concentrated hydrochloric acid deepens the colour. With excess of ammonium hydroxide, brown flocculent ferric hydroxide is precipitated. With potassium ferrocyanide solution, a deep blue colour is obtained in acid solution, whilst with potassium ferricyanide there is no action. Potassium thiocyanate gives in acid solution a deep red colour, which is not d troyed by heat. Salicylic acid gives a violet colour, provided no free mineral acid is present. 

A colorimetric method of estimating small quantities of uranium in solution depends upon the red colour obtained when a uranyl salt is treated with sodium salicylate. Free mineral acid, iron, acetic add, alcohol, or acetone must be absent, but neutral alkali salts do not interfere. 

The titratable acidity at the cation outlet is called the Free Mineral Acidity (EMA) and is related to the Equivalent Mineral Acidity EMA) by the relationship ... 

Messrs. Meister, Lucius, and Briining have recently modified the Holliday process, and adopt a method somewhat resembling the last described. It was found that the presence of free mineral acid in the solution of the diazo-compound is disadvantageous, and that brighter and more even shades are obtained if the free acid is neutralised by addition of chalk, or replaced by acetic acid, this being effected by addition of sodium acetate. The goods are worked first in the phenol dissolved in water in presence of two molecules of caustic soda, dried, passed into the prepared solution of the diazo-compound, and washed till the wash-waters. are colourless. 

Free Mineral Acid H2SO4, HCI, etc. expressed as CaCOa, titrated to methyl orange end-point Corrosion Neutralization with alkalies... 

Huber s reagent. An aqueous solution of ammonium molybdate and potassium ferrocyanide used for detecting free mineral acid. With the exception of boric acid and arsenic trioxide, free mineral acids produce a reddish-brown precipitate, or a turbidity with the reagent. 

---