Electrodes left-hand

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. 

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. 

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. 

Each electrode compartment of a galvanic cell contains a silver electrode and 10.0 ml, of 0.10 M AgN03(aq) they are connected by a salt bridge. You now add 10.0 ml. of 0.10 M NaCl(aq) to the left-hand electrode compartment. Almost all the silver precipitates as silver chloride but a little remains in solution as a saturated solution of AgCI. The measured emf is E = +0.42 V. What is the concentration of Ag+ in the saturated solution ... 

Description of the cell composition is based - as far as possible - on the Stockholm convention (1953), i.e. the left-hand electrode constitutes the negative terminal of the cell. Cells are listed according to the metallic constituent of the electrode mentioned first which is involved in the electrode reaction establishing the respective electrode potential. Contact materials and conductive additives may be mentioned first before the actual element of interest only for the sake of correct materials sequence. The sequence of electrode components is stated as reported in the original publications. When an oxygen electrode is used as reference electrode an oxygen partial pressure of 0.21 atm is assumed. 

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. 

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.

The potential of this electrode is defined (Section 5.2) as the voltage of the cell Pt H2(l atm) H (a = 1) M M, where the left-hand electrode, = 0, is the normal hydrogen reference electrode (described in Section 5.6). In Chapter 6, we derive the Nemst equation on the basis of the electrochemical kinetics. Here we use a simplified approach and consider that Eq. (5.9) can be used to determine the potential E of the M/M electrode as a function of the activity of the products and reactants in the equilibrium equation (5.10). Since in reaction (5.10) there are two reactants, and e, and only one product of reaction, M, Eq. (5.9) yields... 

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 ... 

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 left-hand electrode (anode) is in excess of electrons due to oxidation reaction, it is negative, and... 

Meaning of the positive emf Oxidation occurs at the left-hand electrode. Zn - Zn2+ + 2e... 

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... 

The electric potential difference of a -> galvanic cell (cell voltage) is the difference of electric potential between a metallic terminal attached to the right-hand electrode in the -> cell diagram and identical metallic terminal attached to the left-hand electrode. E includes the condition when current flows through the cell. The value of E measured when the left-hand electrode is at virtual equilibrium, and hence acting as a -> reference electrode, may be called the potential of the (right-hand) electrode with respect to the (left-hand) reference electrode. 

ArG and K apply to the cell reaction in the direction in which reduction occurs at the right-hand electrode and oxidation at the left-hand electrode, in the diagram representing the cell (see p.60). (Note the mnemonic reduction at the right .)... 

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