Zinc sulfate cell electrolyte

At about the same time, Matsushita et al. reported a study of quasi-two-dimensional deposition in a thin layer of electrolyte solution [3], A binary zinc sulfate solution was confined within a planar disk, 17 cm in diameter, bounded on the bottom by a glass plate and on the top by a layer of immiscible organic liquid. Cell potentials of several volts were applied, and the deposits grew along the liquid-liquid interface. In this cell, the depth of solution was 10 cm, but the deposit formed only along the interface between the electrolyte solution and the organic layer. Since a... 

In a Daniell cell, the pieces of metallic zinc and copper act as electrical conductors. The conductors that carry electrons into and out of a cell are named electrodes. The zinc sulfate and copper(II) sulfate act as electrolytes. Electrolytes are substances that conduct electricity when dissolved in water. (The fact that a solution of an electrolyte conducts electricity does not mean that free electrons travel through the solution. An electrolyte solution conducts electricity because of ion movements, and the loss and gain of electrons at the electrodes.) The terms electrode and electrolyte were invented by the leading pioneer of electrochemistry, Michael Faraday (1791-1867). 

During battery discharge, as shown in Figure 1 with the Daniell cell as an example, the electrode (a zinc rod immersed in a zinc sulfate solution) at which the oxidation reaction takes place is called the anode, and is the negative electrode. The other electrode (a copper rod immersed in a copper sulfate solution) at which the reduction reaction takes place is called the cathode and is the positive electrode. The electron flow in the external circuit is from anode to cathode (the current, /, conventionally flows in the opposite direction to that of the electrons), and in the electrolyte phase the ionic flow closes the circuit. The net result of the charge flow round the circuit is the cell reaetion, which is made up of the two half-reactions of charge transfer that describe the chemical changes at the two electrodes. 

Derivation Extracted from ores by two distinct methods, both starting with zinc oxide formed by roasting the ores (1) the pyrometallurgical or distillation process wherein the zinc oxide is reduced with carbon in retorts from which the resultant zinc is distilled and condensed and (2) the hydrometallurg-ical or electrolytic process wherein the zinc oxide is leached from the roasted or calcined material with sulfuric acid to form zinc sulfate solution, which is electrolyzed in cells to deposit zinc on cathodes. 

The fuel cell concept has been known for more than 150 years. It was Christian Friedrich Schonbein who recognized and described the appearance of inverse electrolysis [4] shortly before Sir William Grove, the inventor of the platinum/ zinc battery, constructed his first gas voltaic battery [5]. Grove used platinum electrodes and dilute sulfuric acid as a proton conducting electrolyte. Sulfuric acid is still used today for the impregnation of porous separators serving as the electrolyte in direct methanol laboratory fuel cells [6], but the most commonly used fuel cell electrolytes today are hydrated acidic ionomers. As opposed to aqueous sulfuric acid, where the dissociated protons and the diverse sulfate anions (conjugated... 

The component of the voltaic cell through which ions are able to flow is called the electrolyte. For our voltaic cell, the zinc sulfate solution is the electrolyte in the anode half-cell, and the copper(II) sulfate solution is the electrolyte in the cathode half-cell. 

Figure 14.6-1 Two types of electrochemical cells, (a) A cell with two electrodes and shared electrolyte. One example of such a cell contains a copper electrode, a zinc electrode, and a zinc sulfate and copper sulfate electrolyte solution. The overall cell reaction is Cu" (aq) -)- Zn(s) —> Cu(s) -f Zn" (aq). (b) A cell with two separate compartments connected by a salt bridge. If the same electrodes as in the previous case were used, one compartment would contain a copper electrode and a CuSO solution, the other would have a zinc electrode and a ZnS04 solution as the electrolyte, and the two compartments would be connected by a bridge containing, for example, a sodium chloride solution.

The oxidation half-cell. In this case, the anode compartment consists of a zinc bar (the anode) immersed in a Zn " " electrolyte (such as a solution of zinc sulfate, ZnS04). The zinc bar is the reactant in the oxidation half-reaction, and it conducts the released electrons out of its half-cell. 

Clark cell A type of cell formerly used as a standard source of e.m.f. It consists of a mercury cathode coated with mercury sulfate, and a zinc anode. The electrolyte is zinc sulfate solution. The e.m.f. produced is 1.4345 volts at 15°C. The Clark cell has been superseded as a standard by the Weston (Trademark) cadmium cell. The cell is named for the English engineer Josiah Latimer Clark (1822-98). 

Daniell cell /dan-yel/ A type of primary cell consisting of two electrodes in different electrolytes separated by a porous partition. The positive eletrode is copper immersed in copper(II) sulfate solution. The negative electrode is zinc-mercury amalgam in either dilute sulfuric acid or zinc sulfate solution. The porous pot prevents mixing of the electrolytes, but allows ions to pass. With sulfuric acid the e.m.f. is... 

Other electrolytes, such as sodium sulfate or potassium nitrate, could be chosen for the salt bridge. Neither of these electrolytes interferes in the cell reaction. Silver nitrate, AgN03(aq), would be a poor choice for the salt bridge, however. Positive silver ions would migrate into the half-cell that contains the cathode. Zinc displaces both copper and silver from solution, so both copper(n) ions and silver ions would be reduced at the cathode. The copper produced would be contaminated with silver. 

Iron and aluminum precipitate out when treated with ammonia and are removed by filtration. Other metals, such as copper, zinc, lead and arsenic are precipitated and removed as sulfides upon passing hydrogen sufide through the solution. Colloidal particles of metaUic sulfides and sulfur are removed by treatment with iron(ll) sulfide. The purified solution of manganese(ll) sulfate is then electrolyzed in an electrolytic cell using lead anode and HasteUoy or Type 316 stainless steel cathode, both of which are resistant to acid. Manganese is deposited on the cathode as a thin film. 

After the zinc has been removed, the sulfuric acid rich solution is returned to dissolve the next batch of sludge. Over time, the sodium concentrations will read unacceptable levels in the electrolyte. A bleed stream from the zinc cells is constantly being neutralized and filtered. The saturated sodium sulfate solution thus created is crystallized out as sodium sulfate anhydrous for sale to the pulp and paper industry. Table one shows a complete mass balance for a typical batch. 

Delaurier cell — This was a chromic acid (carbon electrode)-zinc - battery with a chromic acid electrolyte that contained additionally iron(lll) sulfate. See also - chromic acid battery, -> Daniell cell, -> zinc, -> Zn2+/Zn electrodes, -> Zn2+/Zn(Hg) electrodes, -> zinc-air batteries (cell), and - Leclanche cell. 

It is also used for the manufacture of soluble phosphate fertilizers (Chap. 21), of ammonium sulfate for use as a fertilizer, of other sulfates, and in the manufacture of many chemicals and drugs. Steel is usually cleaned of iron rust (is pickled ) by immersion in a bath of sulfuric acid before it is coated with zinc, tin, or enamel. The use of sulfuric acid as the electrolyte in ordinary storage cells has been mentioned (Chap. 14). 

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