Oxidation Cu2

Oxidation of the aldehyde group of an aldose to form a carboxylic acid or carboxylic acid anion is often used analytically to determine the amount of reducing sugar. The Benedict and Fehling methods measure the amount of reducing sugar present in a fluid. In these reactions, the oxidant, Cu2+, is reduced to Cu+. Cu+ precipitates as Cu20, which can be measured in a variety of ways. In the Tollens test, Ag+ is reduced to Ag°. 

With heterocyclic N-oxides lf7rA pyridine N-oxide and derivatives With pyridine N-oxide [Cu2(pyo)4(N03)4] room 1.90 Farad, vib. TIP=60-10 emu/mol spin-spin interaction 73M27,... 

With heterocyclic N-oxides With pyridine N-oxides and derivatives With pyridine N-oxide [Cu2(N03)4(pyo)J 300- 4.2 1.90 2 vib., Farad per copper (II) ion magnetism fitted to 70H8... 

Copper(I) oxide [1317-39-1] is 2lp-ty e semiconductor, Cu2 0, in which proper vacancies act as acceptors to create electron holes that conduct within a narrow band in the Cu i7-orbitals. Nickel monoxide [1313-99-17, NiO, forms a deficient semiconductor in which vacancies occur in cation sites similar to those for cuprous oxide. For each cation vacancy two electron holes must be formed, the latter assumed to be associated with regular cations ([Ni " h = Semiconduction results from the transfer of positive charges from cation to cation through the lattice. Conduction of this type is similar... 

Cu(N03 )26H2 0, is produced by crystallization from solutions below the transition poiat of 26.4°C. A basic copper nitrate [12158-75-7] Cu2(N02)(0H)2, rather than the anhydrous product is produced on dehydration of the hydrated salts. The most common commercial forms for copper nitrate ate the ttihydtate and solutions containing about 14% copper. Copper nitrate can be prepared by dissolution of the carbonate, hydroxide, or oxides ia nitric acid. Nitric acid vigorously attacks copper metal to give the nitrate and evolution of nitrogen oxides. 

Oxidation of Ni by Cu2+. Nickel metal reacts spontaneously with Cu2+ ions, producing Cu metal and Ni2+ ions. Copper plates out on the surface of the nickel, and the blue color of Cu2+ is replaced by the green color of NP+. 

Stable compounds of silver(II) are found with N, O and F as donor atoms macrocycles are, as elsewhere, able to support the higher oxidation state. As a d9 system, Ag2+ imitates Cu2+ in displaying Jahn-Teller distortion. 

The decomposition of diacyl peroxides (36) is catalyzed by various transition metal salts,46,167 for example, Cu+ (Scheme 3.28).168,169 A side reaction is oxidation of alkyl radicals by the oxidized fonn of the metal salt e.g. Cu2+). 

NOTE Cupric copper (Cu2+) is a catalyst for the hydrazine-oxygen reaction, as well as a catalyst for sulfite, DEHA, erythorbic acid, and hydroquinone. Cuprous copper (Cu+) acts as a complexing agent in the desirable formation of protective, pasivated copper oxide films. 

From the first of the two reactions shown, it can be seen that in the acid cleaning solution the cupric ion (Cu2+) is formed from cupric oxide. The thiourea component then reduces the cupric ion to the cuprous ion (Cu+) and, in a series of reactions, complexes it, essentially preventing the cupric ion from ultimately plating out as copper. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

A parallel set of determinations was done with Cu2+ added, since this metal ion has been reported to oxidize the superoxide radical ion very rapidly. Thus, with added Cu2+ the first reaction proceeded as shown, but the second was replaced by... 

Rate expression. The oxidation of SOj- to SO4- by molecular oxygen is catalyzed by traces of Cu2+ and inhibited by small amounts of alcohols. Derive the expression for -d[SO ]/dt by making the usual approximations, assuming the following mechanism ... 

The name of a monatomic cation is the same as the name of the element forming it, with the addition of the word ion, as in sodium ion for Na+. When an element can form more than one kind of cation, such as Cu+ and Cu2+ from copper, we use the oxidation number, the charge of the cation, written as a Roman numeral in parentheses following the name of the element. Thus, Cu+ is a copper(I) ion and Cu2+ is a copper(II) ion. Similarly, Fe2+ is an iron(II) ion and Fe3" is an iron(III) ion. As shown in Fig. C.6, most transition metals form more than one kind of ion so unless we are given other information we need to include the oxidation number in the names of their compounds. 

FIGURE K.5 When a strip of zinc is placed in a solution that contains Cu2 t ions, the blue solution slowly becomes colorless and copper metal is deposited on the zinc. The inset shows that, in this redox reaction, the zinc metal is reducing the Cu2+ ions to copper metal and the Cu2+ ions are oxidizing the zinc metal to Zn2 ions. 

Self-Test 12.9B Which is the stronger oxidizing agent, Cu2+ or Ag in aqueous solution under standard conditions Evaluate the standard emf of the appropriate cell, specify the cell with a cell diagram, and write the net ionic equation for the corresponding cell reaction. 

An electrochemical cell in which electrolysis takes place is called an electrolytic cell. The arrangement of components in electrolytic cells is different from that in galvanic cells. Typically, the two electrodes share the same compartment, there is only one electrolyte, and concentrations and pressures are far front standard. As in all electrochemical cells, the current is carried through the electrolyte by the ions present. For example, when copper metal is refined electrolytically, the anode is impure copper, the cathode is pure copper, and the electrolyte is an aqueous solution of CuS04. As the Cu2f ions in solution are reduced and deposited as Cu atoms at the cathode, more Cu2+ ions migrate toward the cathode to take their place, and in turn their concentration is restored by Cu2+ produced by oxidation of copper metal at the anode. 

FIGURE 12.14 A schematic representation showing the electrolytic process for refining copper. The anode is impure copper. The Cu2 ions produced by oxidation of the anode migrate to the cathode, where they are reduced to pure copper metal. A similar arrangement is used for electroplating objects. 

Copper is refined electrolyticallv by using an impure form of copper metal called blister copper as the anode in an electrolytic cell (Fig. 12.14). The current supply drives the oxidation of the blister copper to copper(II) ions, Cu2+, which are then reduced to pure copper metal at the cathode ... 

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