Copper ions reactions with zinc metal

A salt bridge serves as an ionconducting connection between the two half-cells. When the external circuit is closed, the oxidation reaction starts with the dissolution of the zinc electrode and the formation of zinc ions in half-cell I. In half-cell II copper ions are reduced and metallic copper is deposited. The sulfate ions remain unchanged in the aqueous solution. The overall cell reaction consists of an electron transfer between zinc and copper ions ... 

Let us continue with the example of copper ions in contact with copper metal and zinc ions in contact with zinc metal. This combination is usually referred to as the Darnell cell or zinc/copper couple(Fig. 6.5a). For this electrochemical cell the reduction and oxidation processes responsible for the overall reaction are separated in space one half reaction taking place in one electrode compartment and the other takes place in the other compartment. 

The reaction of zinc metal with copper(II) ions is one example of oxidation-reduction ... 

Reaction of zinc metal with copper ions... 

Organozinc compounds can be prepared by direct metallation of organic halides with zinc metal. The procedure makes the coupling reaction more convenient. A mixture of alkyl halide, acyl chloride, and zinc metal upon stirring in the presence of palladium catalyst at room temperature gives the desired ketone.f - " While direct metallation can be carried out efficiently when the zinc-copper couple is used in some cases, the presence of copper ion sometimes prevents the coupling reaction with acyl chloride.f ... 

As a third oxidation-reduction example, suppose a strip of metallic zinc is placed in a solution of copper nitrate, Cu(N03)j. The strip becomes coated with reddish metallic copper and the bluish color of the solution disappears. The presence of zinc ion, Zn+2, among the products can be shown when the Cu+2 color is gone. Then if hydrogen sulfide gas is passed into the mixture, white zinc sulfide, ZnS, can be seen. The reaction between metallic zinc and the aqueous copper nitrate is... 

The table of standard reduction potentials assists in the determination as to whether species can react with each other, or not. This can be substantiated by considering the reaction of hydrogen with two metals, copper and zinc. In order to determine whether or not a reaction takes place spontaneously under standard conditions, one calculates the standard potential using hydrogen ions and the metal as reactants. 

We now consider a slightly different cell in which the copper half-cell is the positive pole. Perhaps the negative electrode is zinc metal in contact with Zn2+ ions. If the cell discharges spontaneously, then the electron-transfer reaction is the reduction reaction in Equation (7.7) as depicted in the strip cartoon in Figure 7.8. A bond forms between the surface of the copper electrode and a Cu2+ cation in the solution The electrons needed to reduce the cation come from the electrode, imparting a net positive charge to its surface. 

As you learned in Chapter 10, a zinc strip reacts with a solution containing copper(II) ions, forming zinc ions and metallic copper. The reaction is spontaneous. It releases energy in the form of heat in other words, this reaction is exothermic. 

Zinc metal reacts spontaneously with an aqueous solution of copper sulfate when they re placed in direct contact. Zinc, being a more reactive metal than copper (it s higher on the activity series of metals presented in Chapter 8), displaces the copper ions in solution. The displaced copper deposits itself as pure copper metal on the surface of the dissolving zinc strip. At first, the reaction may appecir to be a simple single replacement reaction, but it s also a redox reaction. 

The anodic reaction is an oxidation reaction producing electrons in the anode, while the cathodic reaction is a reduction reaction consuming electrodic electrons at the cathode interface. We shall consider, as an example, an electrochemical cell consisting of a metallic zinc electrode and a metallic copper electrode, in which the anodic reaction of zinc ion transfer (zinc dissolution) is coupled with the cathodic reaction of copper ion transfer (copper deposition) as shown in the following processes ... 

The dissolution of the zinc is no longer inhibited by a buildup of negative charge in the metal, because the excess electrons are removed from the zinc by copper ions that come into contact with it. At the same time, the solution remains electrically neutral, since for each Zn ion introduced to the solution, one Cu ion is removed. The net reaction... 

Quite frequently the natural surface of a mineral requires preliminary chemical treatment before it will form the surface film required for collection One of the commonest instances of this is with sphalerite (zinc sulphide), which does not float properly when treated with xanthates. If, however, it is given a preliminary treatment with dilute copper sulphate solution, a very small amount of copper sulphide is deposited on the surface and the ore becomes floatable, the surface being now capable of reaction with xanthates. Such treatment is usually termed activation in general, an activating solution for a sulphide mineral should contain a metallic ion whose sulphide is less soluble than that contained in the mineral for zinc sulphides, silver, copper, mercury, cadmium, and lead salts are all effective activators. 

The complexation reactions of pilocarpine with cobalt(II), nickel(II), copper(II), and zinc(II) ions were investigated (84). The complexes were characterized by spectrophotometry, conductivity, ESR, NMR, and magnetic susceptibility measurements. In each case, the metal ion was pseudo-tetrahedrally coordinated. Pilocarpine interacts with the metal ion through the imidazole ring. 

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