Copper sulfate solution, electrolysi

Conductance is usually given in the unit Siemens (S = 0 ). The validity of Ohm s law for the case of electrolyte solutions can be experimentally proven (Experiment 21.3 showing electrolysis of a copper sulfate solution with copper electrodes). 

When copper is extracted, in a process similar to that happening in the blast furnace, it is very impure. To purify the copper, it is used as the anode in a very large electrolysis cell containing copper sulfate solution as the electrolyte and a pure copper rod as the cathode. During the process, the anode dissolves and pure copper is deposited on the cathode. The impurities settle at the bottom of the cell. A simplified version of this process can be carried out as a class practical. 

The second law is ejq)lained in a straightforward manner by using the submicroscopic model of electrolytes to interpret the electrolysis phenomenon. In the case of copper deposited on the cathode in the electrolysis of copper sulfate solution, this model is expressed symbolically by the equation of the corresponding reduction half reaction ... 

In his creation of the first electric battery in 1799, Alessandro Volta laid the foundation of electrochemistry. His battery consisted of a zinc and a copper electrode dipped into an aqueous solution of sulfuric acid and connected externally by copper wires. The procedure for setting up and running this experiment is similar to the earlier practical of the electrolysis of aqueous copper sulfate solution (page 265), but without the external power supply. If a voltmeter is connected in parallel to the external circuit, it can be used to measure the potential difference. The half reactions and the overall reaction are as follows ... 

This condition is met in a method called internal electrolysis (or spontaneous electrogravimetric analysis), first described by Ullgren in 1868, in which electrolysis occurs by spontaneous discharge of a galvanic cell. To illustrate the principle, consider two half-cells, comprising a zinc rod in a zinc sulfate solution and a copper rod in a copper sulfate solution. At open circuit, 25 °C, the reversible cell potential is related to the two standard electrode potentials (E°) ... 

Section 23.4 Electrometallurgy is tire use of electrolytic methods to prepare or purify a metallic element. Sodium is prepared by electrolysis of molten NaCl in a Downs cell. Aluminum is obtained in the Hall process by electrolysis of AI2O3 in molten cryolite (NagAlFg). Copper is purified by electrolysis of aqueous copper sulfate solution using anodes composed of impure copper. 

Metallic copper is sometimes obtained by leaching a copper ore with sulfuric acid and then depositing the metal by electrolysis of the copper sulfate solution. Most copper ores, however, are converted into crude copper by chemical reduction. This crude copper is cast into anode plates about 2 cm thick, and is then refined electrolytically. In this process the anodes of crude copper alternate with cathodes of thin sheets of pure copper coated with graphite, which makes it possible to strip off the deposit. The electrolyte is copper sulfate. As the current passes through, the crude copper dissolves from the anodes and a purer copper deposits on the cathodes. Metals below copper in the EMF series, such as gold, silver, and platinum, remain undissolved, and fall to the bottom of the tank as sludge, from which they can be recovered. More active metals, such as iron, remain in the solution. 

In the electrolysis cell used to refine copper, both the anode and the cathode are made of copper (Figure 23.4 ). The anode is the impure copper (that needs to be refined) and the cathode is a thin sheet of pure copper. As the current flows through the cell, the copper from the anode oxidizes and dissolves in a copper sulfate solution. It then plates out as pure copper on the cathode. The impurities in the copper anode separate from the copper during electrolysis becanse, even thongh the more active metals also oxidize from the anode, they stay in solntion and do not plate ont on the cathode. The less active metals do not oxidize at aU and simply fall to the bottom of the cell as the copper is dissolved from the anode. The sludge at the bottom of the electrolysis cell contains many precious metals, including gold and silver. About one-quarter of the silver produced in the United States is from the impurities recovered from the refinement of copper. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

E.8 Copper metal can be extracted from a copper(II) sulfate solution by electrolysis (as described in Chapter 12). If 29.50 g of copper(II) sulfate pentahydrate, CuS04-511,0, is dissolved in 100. mL of water and all the copper is electroplated out, what mass of copper would be obtained ... 

The law may be expressed in an another fashion by stating that the same quantity of electricity is required to liberate 1 g-equiv. of any product of electrolysis. This quantity of electricity is known as the Faraday, and is 96,500 coulombs. To elaborate, let the passage of the same quantity of electricity through two solutions, one of copper sulfate and the other of silver nitrate, be considered. According to Faraday s third law, the ratio of the weights of the copper and the silver deposited is equal to the ratio of the equivalent weights of these two metals. Ionically, the deposition reaction for the two metals considered can be shown as... 

The electrolysis of a copper(II) sulfate solution is now considered in two different situations. In the first, a copper cathode and a platinum or carbon anode are used. The second case involves the use of a copper cathode and a copper anode. The solution has Cu2+ (aq) and S04 (aq) ions from the copper(II) sulfate and H+ (aq) and OH (aq) ions from water. Both Cu2+ (aq) and H+ (aq) ions migrate to the copper cathode, and the Cu2+ ions, being lower in the electrochemical series, discharge in preference to the H+ ions ... 

The influence of antimony at a level of 300 ppm in copper electrolysis is also significant. The morphologies of deposits made from a pure acid-copper sulfate electrolyte and from an identical solution to which the antimony was added are shown in Figures 5 and 6. There are many other combinations of impurities and electrolytes which exhibit this changing surface appearance and deposit orientation besides those selected as examples. Anion effects are also not uncommon, with the halogens often causing the more notable changes. 

Zinc also may be produced by electrolysis of zinc sulfate solution. The zinc oxide in the roasted concentrate is leached with sulfuric acid. The oxide is converted to soluble zinc sulfate. Impurity metals, such as iron, copper, cadmium, arsenic, tin, and cobalt are removed by precipitation, floe formation, and other methods. The purified zinc sulfate solution is electrolyzed using aluminum cathodes and lead anodes. Zinc is deposited on the cathode. 

Figure 5.14 The electrolysis of copper(n) sulfate solution using inert electrodes.

Figure 11.16 Schematic of copper recovery by coupled transport from dump leach streams. The concentrated copper solution produced by coupled transport separation of the dump leach liquid is sent to an electrolysis cell where copper sulfate is electrolyzed to copper metal and sulfuric acid...

Cathodic reduction is also used to purify some metals, such as copper. Slabs of impure copper serve as the anode, while a pure copper sheet serves as the cathode in an undivided electrolytic cell. The electrolytic bath is copper(II) sulfate. During electrolysis, Cu2+ ions leave the anode and plate on the cathode. Impurity metals more reactive than copper are oxidized and stay in solution. Less reactive metals collect at the bottom of the cell. After about a month, the enlarged copper cathodes are removed (Ebbing and Gammon, 2005). Metals can also be oxidized electrolytically at the anode (anodized). It is even possible to further oxidize some metals in a low oxidation state to a higher oxidation state. 

A 1.0 molar solution of copper sulfate is electrolyzed with an inert, e.g., platinum, anode and a copper cathode of 55 sq. cm. exposed area the current is maintained constant at 0.040 amp. If the electrolysis vessel contains 1 liter of solution and there is reasonable circulation of the electrolyte, without resort to stirring, estimate approximately how long electrolysis will proceed before hydrogen evolution commences. How much of the original copper will then have been deposited ... 

The major technical factors in electrorefining are cathode purity, production rate, and specific energy consumption. These factors are influenced primarily by anode quality, electrolyte conditions, and cathode current density. The electrolysis is performed in a solution of copper sulfate and sulfuric acid with a nominal composition of40-45 g L-1 copper and 160-200 g L-1 sulfuric acid at 60-66 °C with a current... 

To illustrate the Hittorf method for measuring the contribution of the individual ions to the current, we consider the electrolysis cell shown in Fig. 31.4. Suppose that the solution contains copper sulfate and that the anode is copper. We examine the changes that occur in each compartment if one mole of electricity passes. These changes are summarized in Table 31.4. If a quantity of electricity Q passes, this is Q/F moles, so all of the changes are... 

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