Oxidation acid concentration

The unique behaviour of Cu in the first transition series, having a positive (M2 + /M) value, accounts for its inability to liberate H2 from dilute acids (/.< . those with a molar concentration of l mol dm-3). Only oxidizing acids (concentrated nitric and hot concentrated sulfuric) react with Cu, the acids being reduced. The reason for this behaviour is the high energy needed to transform Cu(s) to Cu2 + (g), which is not exceeded by the hydration enthalpy of the ion. 

Silver is a white, lustrous, soft, and malleable metal (mp 961°C) with the highest known electrical and thermal conductivities. It is chemically less reactive than copper, except toward sulfur and hydrogen sulfide, which rapidly blacken silver surfaces. The metal dissolves in oxidizing acids (concentrated HN03) and in cyanide solutions in the presence of oxygen or hydrogen peroxide. 

Concentrated hydrochloric acid is an excellent solvent for inorganic samples but finds limited application in the decomposition of organic materials. It is widely used to dissolve many metal oxides as well as metals more easily oxidized than hydrogen often, it is a better solvent for oxides than the oxidizing acids. Concentrated hydrochloric acid is about 12 M. On heating, however, HCl gas is lost until a constant-boiling 6 M solution remains (boiling point about 110°C). 

Oxidizing acids, concentrated Very poor Very poor ... 

Oxidizing acids, concentrated Alkalies, weak Good Poor No effect Poor... 

Oxidizing acids, concentrated Poor Poor Excellent... 

Oxidizing acids, concentrated Excellent Fair to good Poor to fair... 

Ethylene-tetrafluoroethylene terpolymers are resistant to stress cracking and chemical attack hy most compounds. Strong oxidizing acids, concentrated boiling sulfonic acids and organic bases (amines) attack ETFE and any chemical that affects PTFE, PFA, or FEP. 

Unlike phosphorus pentoxide, this oxide cannot be made directly. Arsenic(V) acid, H3ASO4 (strictly, tetraoxoarsenic acid), is first prepared by oxidising arsenic(III) oxide with concentrated nitric acid or some other strong oxidising agent ... 

If a chloride is heated with manganese(IV) oxide and concentrated sulphuric acid, chlorine is evolved. 

Hence, under ordinary conditions, manganeseflV) oxide oxidises concentrated hydrochloric acid to chlorine, but the above shows that the oxidation process is essentially ... 

METHOD 2 [113]-Phenol can be oxidized with either performic, formic or acetic acids to catechol. For example phenol, formic acid, concentrated H2O2 and polyphosphoric acid are heated 2 hours at 80 C to give 53% catechoi. Addition of phosphorus pen-toxide (P2O5) is said to increase the yieid. 

The practical problems He ia the separatioa of the chlorine from the hydrogea chloride and nitrous gases. The dilute nitric acid must be reconcentrated and corrosion problems are severe. Suggested improvements iaclude oxidation of concentrated solutions of chlorides, eg, LiCl, by nitrates, followed by separation of chlorine from nitrosyl chloride by distillation at 135°C, or oxidation by a mixture of nitric and sulfuric acids, separating the... 

Dead Seas Periclase Ltd., on the Dead Sea in Israel, uses yet another process to produce magnesium oxide. A concentrated magnesium chloride brine processed from the Dead Sea is sprayed into a reactor at about 1700°C (127,128). The brine is thermally decomposed into magnesium oxide and hydrochloric acid. To further process the magnesia, the product is slaked to form magnesium hydroxide which is then washed, filtered, and calcined under controlled conditions to produce a variety of MgO reactivity grades. A summary of MgO purities, for the various processes is given in Table 20. 

The Mn ion is so unstable that it scarcely exists in aqueous solution. In acidic aqueous solution, manganic compounds readily disproportionate to form Mn ions and hydrated manganese(IV) oxide, Mn02 2H20 in basic solution these compounds hydroly2e to hydrous manganese(III) oxide, MnO(OH). Sulfuric acid concentrations of about 400 450 g/L are required to stabilize the noncomplexed Mn ion in aqueous solutions. 

Zinc and Zinc Alloys. Zinc metal is highly reactive in acid solutions such as sulfuric, hydrochloric, and nitric dissolving rapidly at acid concentrations normally used to pickle steel and aluminum. Dilute (1—4%) solutions of these acids can be used with caution to remove zinc oxides. 

Depending on acid concentration, temperature, and the reduciag agent iavolved, any of the foUowiag oxidations may occur ... 

Hydrochloric acid reacts with sulfur only in the presence of iron to form hydrogen sulfide. Sulfur dioxide forms when sulfur is heated with concentrated sulfuric acid at 200°C. Dilute nitric acid up to 40% concentration has Htde effect, but sulfur is oxidized by concentrated nitric acid in the presence of bromine with a strongly exothermic reaction (19). 

The sulfur trioxide produced by catalytic oxidation is absorbed in a circulating stream of 98—99% H2SO4 that is cooled to approximately 70—80°C. Water or weaker acid is added as needed to maintain acid concentration. Generally, sulfuric acid of approximately 98.5% concentration is used, because it is near the concentration of minimum total vapor pressure, ie, the sum of SO, H2O, and H2SO4 partial pressures. At acid concentrations much below 98.5% H2SO4, relatively intractable aerosols of sulfuric acid mist particles are formed by vapor-phase reaction of SO and H2O. At much higher acid concentrations, the partial pressure of SO becomes significant. 

In the reaction of ethylene with sulfuric acid, several side reactions can lead to yield losses. These involve oxidation, hydrolysis—dehydration, and polymerization, especially at sulfuric acid concentrations >98 wt % the sulfur thoxide can oxidize by cycHc addition processes (99). 

Tantalum is not resistant to substances that can react with the protective oxide layer. The most aggressive chemicals are hydrofluoric acid and acidic solutions containing fluoride. Fuming sulfuric acid, concentrated sulfuric acid above 175°C, and hot concentrated aLkaU solutions destroy the oxide layer and, therefore, cause the metal to corrode. In these cases, the corrosion process occurs because the passivating oxide layer is destroyed and the underlying tantalum reacts with even mild oxidising agents present in the system. 

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