Sulphurous acids, stability

Nitrogen content 0/ /o Sulphuric acid Stabilization boiling, hr ... 

Concentrated sulphuric acid and nitric acid—powerful oxidising agents—attack all the elements except nitrogen, particularly when the acids are warm. The products obtained reflect changes in stability of the oxidation states V and III of the Group V elements. 

The properties of the polyurethane moulding compositions are also very similar to nylon 66. The greatest difference in properties is in water absorption, the 6,4-polyurethane absorbing only about of that of nylon 66 under comparable conditions. This results in better dimensional stability and a good retention of electrical insulation properties in conditions of high humidity. Resistance to sulphuric acid is somewhat bettter than with nylon 66 but both types of polymer are dissolved by phenols and formic acid. 

The resistance of rhodium to chemical attack is remarkable, and surpasses that of platinum. Its domain of stability (as seen from Fig. 6.4) is extremely wide, and in the absence of complexing agents it is stable in aqueous solutions of all pH values. In the massive form it is unattacked by caustic alkalis, acids and oxidising agents, including aqua regia. When finely divided, however, it is attacked by concentrated sulphuric acid and aqua regia. 

Cerium(IV) sulphate solutions are remarkably stable over prolonged periods. They need not be protected from light, and may even be boiled for a short time without appreciable change in concentration. The stability of sulphuric acid solutions covers the wide range of 10-40 mL of concentrated sulphuric acid per litre. It is evident, therefore, that an acid solution of cerium(IV) sulphate surpasses a permanganate solution in stability. 

Starch nitrated by Brown and Miliar (Ref 10) by dissolution in nitric acid and subsequent precipitation with the help of sulphuric acid, was stabilized by washing in ether and chloroform... 

Although there are a number of reports in the literature of this process, (see ref. 1) only one of these relates to a kinetic study of the reaction168. The ease with which the reaction takes place depends upon the stability of the leaving carbonium ion. Consequently, de-r-butylation is mcst frequently observed and in a kinetic study of the sulphonation of /-butylbenzene in aqueous sulphuric acid (see p. 72) this side reaction was sufficiently prominent for rates to be easily measurable (Table 225)168. Comparison of the rates with those in Table 42 shows that de-... 

There are extensive data for the acid-catalyzed protiodesilylation of XCgELrSiMes in methanol-aqueous perchloric acid or acetic acid-aqueous sulphuric acid at 50°C225. Correlation analysis of the partial rate factors (relative rate constants) by means of the Yukawa-Tsuno equation (Section n.B) finds p = —5.3 and r+ = 0.65. These values are consistent with a relatively low demand for stabilization of the transition state by electron delocalization, i.e. the transition state is early along the reaction coordinate, p-NO2 is highly deactivating with / = 14 x 10 but 0-NO2 is even more deactivating, with / = 6.8 x 10-5. This contrasts with the deactivation order discussed above for nitration and chlorination (Table 6), and may be explained in terms of the early transition state, well removed from the Wheland intermediate. 

Nakagami and Yokota (1983) impregnated wood with a solution containing methacrylic acid, trifluoracetic acid and sulphuric acid, to form a covalent bond with the cell wall polymers. The methacrylic-reacted wood was then impregnated with styrene, or methylmethacrylate, to form cross-links with the reacted cell wall polymers. Improved dimensional stability was obtained, although degradation of the wood was also observed. 

The new compounds M3[Nb(02)2F4],nH20 and M3[Ta(02)2F4],nH20 (M = NH4, n = 0 M = K or Na, n = 1) have been prepared, and i.r. and conductivity studies suggest that they involve eight-co-ordinate metal atoms. The stability constants of the niobium(v)-peroxide complexes formed in sulphuric acid solutions have been determined. ... 

The pH of pure (and also not so pure) water is very sensitive to small concentrations of acids and bases. One drop of concentrated sulphuric acid added to a liter of water will change the pH by 4 pH nnits (from 7 to ca. 3). Solntion pH can be stabilized by a buffer (although there may be cases where a stable pH is not desirable) addition of (not too large) quantities of acid or base to a buffered solution will not affect the pH mnch. Buffers are usually mixtures of weak acids or bases and their salts. A common example in CD is the nse of an ammoninm salt (NH4X ) to control the pH of an ammonia solntion. The equilibrium of ammonia in water is given by... 

The isothermal solubility curve of mixtures of potassium sulphate and sulphuric acid expresses the composition of the soln. at 25° in equilibrium with the solid phase or phases, when the mol. ratio of K2SO4 and SO3 per 1000 grms. of soln. are plotted as co-ordinates. The ranges of stability in the ternary system K20—S03—H20, are diagrammed in Fig. 51, where the conditions have been studied in the vicinity of the SOs-apex, as far as the formation of KHS207, hut not as far as the well-known potassium pyrosulphate. The meaning of the diagram... 

Action of Sulphuric Acid on Metals. Pour 2-3 ml of concentrated sulphuric acid into a test tube and lower several pieces of iron wire into it. What is observed Carefully heat the test tube. Do you notice any change now What properties does sulphuric acid exhibit in this case What is the difference between the action of concentrated and dilute sulphuric acid on metals What explains the greater strength and stability of sulphuric acid in comparison with sulphurous acid ... 

Nitramine has explosive properties but it is not of any practical value for many reasons, primarily because of its high reactivity which impairs its chemical stability. It decomposes at a temperature as low as its melting point. At room temperature it decomposes slowly, to form nitrous oxide and water. On heating to 60-65°C decomposition occurs in an aqueous solution. It decomposes explosively on contact with concentrated sulphuric acid. ... 

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