Right-hand electrode

Any inert metallic component of an electrode is written as the outermost component of that electrode in the cell diagram. For example, a hydrogen electrode constructed with platinum is denoted H+(aq) H2(g) Pt(s) when it is the right-hand electrode in a cell diagram and Pt(s) H2(g) H+(aq) when it is the left-hand electrode. An electrode consisting of a platinum wire dipping into a solution of iron(II) and iron(III) ions is denoted either Fe3+(aq),Fe2 (aq) Pt(s) or Pt(s) Fe3+(aq),Fe2+(aq). In this case, the oxidized and reduced species are both in the same phase, and so a comma rather than a line is used to separate them. Pairs of ions in solution are normally written in the order Ox,Red. 

In summary, the sign of the emf reported in conjunction with a cell diagram is the same as the sign of the right-hand electrode in the diagram. 

A cell diagram corresponds to a specific cell reaction in which the right-hand electrode in the cell diagram is treated as the site of reduction and the left-hand electrode is treated as the site of oxidation. The sign of the emf then distinguishes whether the resulting reaction is spontaneous in the direction written ( > 0) or whether the reverse reaction is spontaneous ( < 0). 

The standard potential of a couple is the standard emf of a cell (including the sign) in which the couple forms the right-hand electrode in the cell diagram and a hydrogen electrode forms the left-hand electrode in the cell diagram. 

STRATEGY Find the standard potentials of the two reduction half-reactions in Appendix 2B. The couple with the more positive potential will act as an oxidizing agent (and be the site of reduction). That couple will be the right-hand electrode in the cell diagram corresponding to the spontaneous cell reaction. To calculate the standard emf of the cell, subtract the standard potential of the oxidation half-reaction (the one with the less-positive standard potential) from that of the reduction half-reaction. To write the cell reaction, follow the procedure in Toolbox 12.2. 

Therefore, by measuring E, we can infer the concentration of Ag in the left-hand electrode compartment. If the concentration of Ag+ ions in the left-hand electrode is less than that in the right, then E > 0 for the cell as specified and the right-hand electrode will be found to be the cathode. 

The type of electrode reaction that will occur depends on the electrode and electrolyte and also on external conditions the temperature, impurities that may be present, and so on. Possible reactants and products in these reactions are (1) the electrode material, (2) components of the electrolyte, and (3) other substances (gases, liquids, or solids) which are not themselves component parts of an electrode or the electrolyte but can reach or leave the electrode surface. Therefore, when discussing the properties or behavior of any electrode, we must indicate not merely the electrode material but the full electrode system comprising electrode and electrolyte as well as additional substances that may be involved in the reaction for example, ZnCl2, ag I (Clj), graphite [the right-hand electrode in (1.19)]. 

If al>a2y then short circuiting of this cell results in potassium dissolution at the left-hand electrode and incorporation into the amalgam at the right-hand electrode. Amalgam electrodes can be used as reversible electrodes, even for metals as reactive as the alkali metals, especially in some non-aqueous solvents. 

As shown in Fig. 6-3, it is also in the same TUPAC convention that a positive electric charge flows from the left hand electrode through the electrolyte to the right hand electrode, as the cell reaction proceeds in the direction as written in Eqn. 6-3. This defines the sign of the electromotive force of electrochemical cells. 

The electromotive force of an electrochemical cell is the difference in electrode potential between the two electrodes in the cell. According to the TUPAC convention, the electromotive force is the potential of the right hand electrode referred to the potential of the left hand electrode. We consider, for example, a hydrogen-oxygen cell shown in Fig. 6—4 the cell reaction is given by Eqn. 6-1 and the cell diagram is given by Eqn. 6-5 ... 

From the electrode reactions in equilibrium at the left hand electrode (anode) and at the right hand electrode (cathode), we obtain the real potential, a., of electrons in the two electrodes as shown in Eqns. 6-6 and 6-7 ... 

Cells. An electrochemical cell comprises two (or more) redox couples, with the energy of each being monitored by an electrode. (As we have seen already, the electrode may itself be one part of the redox couple.) By convention, we say that the more positive electrode is the right-hand electrode, while the left-hand electrode is the more negative. The difference in potential between the right-hand and left-hand electrodes is called the cell emf ... 

Now consider a new situation, in which we have removed the voltmeter and directly joined the two electrodes. As seen before. Reduction occurs at the Right-hand electrode (notice the alliteration), while oxidation occurs at the left, i.e. the right-hand electrode is positive and the left-hand electrode is negative. These potentials are not absolute - the terms negative and positive are relative, and relate to the potential of one electrode with respect to the other. 

Starting from the right-hand electrode in Figure 5.2 and proceeding clockwise, keeping the order of the symbols of substances the same as written in the schematic representation of the cell, one obtains... 

Figure 5.2. The potential difference across the electrochemical cell, S, is the difference between the potential of the right-hand electrode E and the potential of the left-hand electrode Ei.

When Er is larger than Ei, reduction occurs at the right-hand electrode [Eqs. (9.4) and (9.6)]. Thus, when S > 0, the overall displacement deposition reaction [Eqs. (9.1) and (9.7)] will occur from left to right. The reaction is spontaneous (feasible) in a direction from left to right since AG is negative for pKJsitive values of [Eqs. (9.8) and (9.9)]. This is in agreement with earlier discussions in Chapter 5 and Eigure 5.10. 

Oxygen gas is reduced to at the right-hand electrode (C). The oxide ions are able to pass through the doped zirconia and are oxidised to oxygen gas at the left-hand electrode (A). The equation for the cell reaction is ... 

According to the international convention, the standard potential of the electrode on the left is always subtracted from that of the right-hand electrode. From Eq. (7.282), one has... 

We always attach the left-hand electrode to the negative terminal of the potentiometer and the right-hand electrode to the positive terminal. The voltage on the meter is the difference ... 

Voltage = right-hand electrode potential -left-hand electrode potential... 

Because the voltage is positive, the net reaction is spontaneous in the forward direction. Cd(.v) is oxidized and Ag+ is reduced. Electrons flow from the left-hand electrode to the right-hand electrode. 

FIGURE 12.7 The cell potential can be thought of as being the difference of the two potentials produced by the two electrodes. The cell potential is positive if the right-hand electrode in the cell diagram (the cathode) produces a higher potential than the left-hand electrode (the anode), as indicated here. 

Since the right-hand electrode (cathode) is in deficit of electrons due to reduction reaction, it is positive. 

Left-hand electrode Right-hand electrode... 

Note that there is no direct transference of the electrolyte (HC1) from one side to the other. HCI is removed from the left-hand side by the left-hand electrode reaction and it is added to the right-hand side by the right-hand electrode reaction. This cell is an example of a electrolyte concentration cell without transference. 

Defining as the potential of the right-hand electrode E2, measured with respect to the left-hand electrode j, we may write Ecen as... 

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