Electrochemical Daniell cell

An electrochemical reaction is said to be polarized or retarded when it is limited by various physical and chemical factors. In other words, the reduction in potential difference in volts due to net current flow between the two electrodes of the corrosion cell is termed polarization. Thus, the corrosion cell is in a state of nonequilibrium due to this polarization. Figure 4-415 is a schematic illustration of a Daniel cell. The potential difference (emf) between zinc and copper electrodes is about one volt. Upon allowing current to flow through the external resistance, the potential difference falls below one volt. As the current is increased, the voltage continues to drop and upon completely short circuiting (R = 0, therefore maximum flow of current) the potential difference falls toward about zero. This phenomenon can be plotted as a polarization diagram shown in Figure 4-416. 

One of the most well-known electrochemical cells that is used for the conversion of chemical energy into electrical energy is the Daniell cell... 

During the operation of the cell (or during the direct interaction of zinc metal and cupric ions in a beaker) the zinc is oxidised to Zn and corrodes, and the Daniell cell has been widely used to illustrate the electrochemical mechanism of corrosion. This analogy between the Daniell cell and a corrosion cell is perhaps unfortunate, since it tends to create the impression that corrosion occurs only when two dissimilar metals are placed in contact and that the electrodes are always physically separable. Furthermore, although reduction of Cu (aq.) does occur in certain corrosion reactions it is of less importance than reduction of HjO ions or dissolved oxygen. 

Figure 3.1 Schematic representation of a non-sophisticated cell for equilibrium electrochemical measurements. The example shown is a Daniell cell comprising Cu +,Cu and Zn, Zn half cells. The need for the glass sleeves is discussed in Chapter 9.

We will illustrate the above point with the following example. Consider the cell Zn I ZnS04(aq) 11 CuS04(aq) Cu, which is commonly called the Daniell cell. The actual process of cell discharge involves an electrochemical reaction at both electrodes. Since the zinc is the more negative of the two half cells, oxidation would occur on the zinc side of the cell, as follows ... 

Figure 14.5 shows the basic arrangement of a electrochemical cell called the Daniell cell. This cell is named for John Frederick Daniell (1790-1845) who constructed this type of cell in 1836. The Daniell cell components include zinc and copper solutions in separate containers. Between the solutions is a salt bridge... 

The Daniell cell illustrates the basic features of an electrochemical cell. Electrochemical cells always involve a redox reaction. Oxidation occurs at the cathode of the cell and reduction takes place at the anode. Electrons always flow from the anode to the cathode. Electrochemical cells come in many arrangements. To gain an appreciation for the variety of electrochemical cells, consider all the types of batteries available. 

Reaction (4.2) may be carried out by adding metallic zinc to a solution of copper sulfate or by using an electrochemical cell in which the reactants are not in contact. One such cell (a modern form of a Daniell cell) is shown in Figure 4.1. 

In some cases, as in reactions in electrochemical cells or other reactions involving oxidation-reduction, the half reactions of the ions are useful. Consider the Daniell cell, which consists of a zinc electrode in a zinc sulfate solution, and a copper electrode in a copper solution, the two solutions being separated by a porous partition. The half reactions are... 

An electrochemical cell is an experimental apparatus for generating electricity by using a redox reaction. The Daniel cell for the system Zn(s) + C oi) Zn(aq) + Cu(s) is shown in Figure 1.2. 

In corrosion the dynamic electrochemical processes are of importance and hence considerations of the consequences of perturbation of a system at equilibrium are considered. Let us consider the familiar Daniel cell consisting of copper metal in copper sulfate, and zinc metal in zinc sulfate solution. This, as depicted in Figure 1.18 gives an electromotive force of 1.1 V when there is no current flow. When a small current flows through the resistance R, the potential decreases below 1.1 V. On continued flow of current, the potential difference between the electrodes approaches a value near zero, and... 

Daniell cell — Electrochemical primary cell composed of a zinc and a copper electrode. Both metals are immersed into aqueous solutions of their respective sulfates (described according to the -> Stockholm convention), the solutions are separated by, e.g., a porous glass frit ... 

Barral, F.L., Fernandez, E.G.-F. Secondary students interpretations of the process occurring in an electrochemical cell. Journal of Chemical Education 69 (1992), 655 Bou Jaoude, S.B. A study of the nature of students understanding about the concept of burning. Journal of Research in Science Teaching 28 (1991), 689 Boulabiar, A., Bouraoui, K., Chastrette, M., Abderrabba, M. A historical analysis of the Daniell Cell and elektrochemistry teaching in French and Tunisian textbooks. Journal of Chemical Education 81 (2004), 754... 

The conventional notation for representing electrochemical cells is the cell diagram. For the Daniell cell shown in Figure 19.1, if we assume that the concentrations of Zn + and Cu ions are 1 M, the cell diagram is... 

What is the difference between an electrochemical cell (such as a Daniell cell) and an electrolytic cell ... 

Discuss the processes occurring in the following electrochemical set up. A Daniell cell is being used to generate an electric current which causes electrolysis in a solution of AgNOsCaq). The electrodes are Ag(s) wires dipping into the AgN03(aq) solution. It is observed that electrons flow from the Zn(s) electrode of the Daniell cell to the electrolytic cell, and from the electrolytic cell back to the Cu(s) electrode of the Daniell cell. 

The Daniell cell is an example of a galvanic cell, in this type of electrochemical cell, electrical work is done by the system. The potential difference, between the two half-cells can be measured (in volts, V) on a voltmeter in the circuit (Figure 7.1) and the value of is related to the change in Gibbs energy for the cell reaction. Equation 7.9 gives this relationship under standard conditions, where is°ceu is the standard cell potential. 

A simple example of an electrochemical cell is the Daniell cell, named after the English chemist John Frederic Daniell (1790-1845). This apparatus, illustrated in Figure 8.1, consists of a zinc electrode immersed in a zinc sulfate solution and a copper electrode immersed in a cupric sulfate solution. The two solutions are separated by a porous partition which is of such a nature that it prevents the bulk mixing of the solutions but allows ions to pass through as the cell operates. The emf developed in the Daniell cell depends upon the concentrations of and Cu " ions in the two solutions. If the concentrations of the two solutions are both one mola (1 m), the cell is called a standard cell. 

The Daniell cell is a typical example of what is known as a galvanic vokaic, or electrochemical ceil The fact that the electrons flow from the zinc to the copper electrode indicates that the tendency for Zn + 2e" to occur is greater than... 

Daniell cell shown in Fig. 17.1, a zinc electrode is immersed in a solution of zinc sulfate and a copper electrode is immersed in a solution of copper sulfate the solutions are in electrical contact through a porous partition that prevents the solutions from mixing. The Daniell cell can produce electrical work which is related to the decrease in Gibbs energy, —AG, of the chemical reaction by relation (10.14). If the cell operates reversibly, then the electrical work produced is equal to the decrease in Gibbs energy. The performance of the electrochemical cell is discussed in detail in Chapter 17. 

Consider the electrochemical cell, the Daniell cell, shown in Fig. 17.1. It consists of two electrode systems—two /zu/f-ce//s—separated by a salt bridge, which prevents the two solutions f rom mixing but allows the current to flow between the two compartments. Each half-cell consists of a metal, zinc or copper, immersed in a solution of a highly soluble salt of the metal such as ZnS04 or CUSO4. The electrodes are connected to the exterior by... 

In many secondary school textbooks, the topic of electrochemical cells is introduced after redox reactions by demonstrating a galvanic cell, very often the Daniell cell (zinc-copper cell). But for students, this experiment is overwhelming because of this cell does not look like a battery. Moreover, the experiment is confusing for students because of the large number of new phenomena and the complexity of the explanations. We would propose to start with a more simple experiment that clarifies some basic characteristics of cells, especially the concepts of electrolyte, electrode and electrode reaction. 

When a voltmeter is used for measuring a voltage, the measured quantity is always that of the potential difference between two metals ofthe same nature (following the measuring principle of a voltmeter). The electrochemical chain corresponding to the measure of the voltage of the Daniell cell Is ... 

The second example deals with a Daniell cell, and shows to what extent the solution that is contained within the salt bridge has an impact on the overall ionic junction voltage. Here the voltage is the algebraic sum of two liquid Junction voltages, illustrated by the following electrochemical chain ... 

Dioxygen, like the copper electrode in Daniell cell, receives the two electrons and is the right end of the electrochemical cell we re-write its reductive half-reaction as follows ... 

The theoretical voltage of an electrochemical cell is equal to the difference between the reversible potentials of the two electrode reactions, as calculated by the Nernst equation. For the Daniell cell (Figure 2.10), the theoretical voltage is given by ... 

Inzelt G (2008) Daniell, John Frederic and Daniell cell. In Bard AJ, Inzelt G, Scholz F (eds) Electrochemical dictionary. Springer, Berlin, p 81... 

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