Series electrochemical

The electrochemical series [Ch ter 10, Table 10.13] or, in fact, a list of the standard electrode potentials for reduction half-reactions can be very useful to quickly calculate the standard value of the potential. An example of the electrochemical series just for a few electrochemical half-reactions taken from [Chapter 10, Table 10.13] is given in Table 4.1. 

Selected Standard Electrode Potentials in Alphabetical Order and the Order from the Most Positive in the Top to the Most Negative in the Bottom for Demonstrating So-Called Electrochemical Series 

EP values ordered from the most positive in the top to the most negative in the bottom 

Source Haynes, W.M. (Editor-in-Chief), Hrmdbock of Chemistry and Physics, 95th edn., CRC Press, Boca Raton, FL, 2014—2015. 

Note The full list of reactions is given in Chapter 10, Table 10.13. 

Standard potentials are sometimes called reduction potentials. The more negative the value of the reduction potential, the more difficult it is to reduce the positive ion to metal. If electrode reactions are ordered according to standard potentials, the electrochemical series (Table 10.1) is obtained. First in the series is the reduction reaction that occurs most easily, as in this case, the reduction of Au+ to gold metal. The precious metals appear high up on the list. At the bottom we find alkali metal ions, which are the most difficult to reduce to metals. At the same time, alkali metals most easily oxidize to metal ions. Zero is set for the reaction where Hj is split into 

The half-reactions may be added or subtracted to obtain a full reaction. If 0, AG 0 and the reaction occurs spontaneously. Equation 10.16 is used to obtain AG. AG for the sum reaction is obtained. Finally, the value of E is obtained. 

The values used in Table 10.1 refer to standard potentials measured in water solution under standard conditions. Concentrations change the values according to Equation 10.17. Furthermore, acidity and complex formation are important. In proteins and solids, there may be great differences due to protein structme and CTystal structure, respectively. 

Reaction of Metals with Salts. 1. Pour a small amount of a copper 

Immerse an iron plate into a test tube containing a lead acetate solution. 

Note the observed phenomena. Write the molecular and net ionic equations of the reactions occurring between the metals and the salts. Arrange the metals in a series according to their activity (the electrochemical series), writing down the values of their standard electrode potentials (see Appendix 1, Table 2). What place does hydrogen occupy in this series  

Reaction of Non-Metals with Salts. 1. Add 0.5 ml of petrol and several drops of chlorine water to each of potassium bromide and iodide solutions. Stir the solutions with a glass rod. Note the colour of the petrol layer. Write the equations of the reactions in the molecular and net ionic forms. 

5 ml of petrol and a few drops of bromine water to a potassium iodide solution. How can the change in the colour of the petrol solution be explained Write the equation of the reaction. 

Reaction of Metals with Salts. 1. Pour a small amount of a copper sulphate solution into two test tubes. Immerse an iron plate or nail into one of them and a piece of lead into the other. 

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Metallic gold, which is found free in nature, has always been valued for its nobility, i.e. its resistance to chemical attack. This property is to be expected from its position in the electrochemical series. It... 

Almost all common metals and structural steels are liable to corrode in seawater. Regulations have to be followed in the proper choice of materials [16], In addition, there is a greater risk of corrosion in mixed constructions consisting of different metals on account of the good conductivity of seawater. The electrochemical series in seawater (see Table 2-4), the surface area rule [Eq. (2-44)] and the geometrical arrangement of the structural components serve to assess the possibility of bimetallic corrosion (see Section 2.2.4.2 and Ref. 17). Moreover the polarization resistances have considerable influence [see Eq. (2-43)]. The standards on bimetallic corrosion provide a survey [16,17]. 

The ease with which an atom gains or loses electrons is termed die electronegativity of die element. Tabulation of die elements in order of ease hy which diey lose electrons is called die electrochemical series and is shown in Table 6.10. Chapter 4 explains die importance of diis to die formation and control of coiTosion, and Chapter 6 discusses die relevance to predicting reactivity of metals towards water and their potential to become pyrophoric. 

Alumiojuffl resists corrosion not because of its position in the electrochemical series but because of the ra Hd formation of a coherent, inert, oxide layer. Contact with grafihite, Fe. Ni. Cu, Ag or Pb is disastrous for corrosion resistance, the effect of contact with steel, Zn and Cd depends on pH and exposure conditions. Protection is enhanced by anodizing the metal this involves immersing it in 15-20% H2SO4 and connecting it to the positive terminal so that it becomes coated with alumina ... 

In the electrochemical series of elements, copper is near the noble end and will not normally displace hydrogen, even from acid solutions. Indeed, if hydrogen is bubbled through a solution of copper salts, copper is slowly deposited (more rapidly if the process is carried out under pressure). (See Section 1.2 for thermodynamic considerations.)... 

Nickel occupies an intermediate position in the electrochemical series Ni2 /Ni = -0-227 V, so that it is more noble than Zn and Fe but less noble than Sn, Pb and Cu. Figure 4.21 shows a revised potential-pH equilibrium (Pourbaix) diagram for the Ni-H O system at 25°C. The existence of the higher anhydrous oxides Nij04, NijO, and NiOj shown in an earlier diagram appears doubtful in aqueous systems in the absence of positive identification of such species. It is seen that ... 

Zinc is relatively low in the electrochemical series and is widely regarded as an active metal. However, when high-purity zinc is placed in hydrochloric acid it will dissolve extremely slowly, if at all. It may be encouraged to... 

When metals are arranged in the order of their standard electrode potentials, the so-called electrochemical series of the metals is obtained. The greater the negative value of the potential, the greater is the tendency of the metal to pass into the ionic state. A metal will normally displace any other metal below it in the series from solutions of its salts. Thus magnesium, aluminium, zinc, or iron will displace copper from solutions of its salts lead will displace copper, mercury, or silver copper will displace silver. 

Concentrated hydrochloric acid will dissolve many metals (generally those situated above hydrogen in the electrochemical series), as well as many metallic oxides. Hot concentrated nitric acid dissolves most metals, but antimony, tin and tungsten are converted to slightly soluble acids thus providing a separation of these elements from other components of alloys. Hot concentrated sulphuric acid dissolves many substances and many organic materials are charred and then oxidised by this treatment. 

Electrical units 503, 519 Electrification due to wiping 77 Electro-analysis see Electrolysis and Electrogravimetry Electrochemical series 63 Electro-deposition completeness of, 507 Electrode potentials 60 change of during titration, 360 Nernst equation of, 60 reversible, 63 standard 60, (T) 62 Electrode reactions 505 Electrodeless discharge lamps 790 Electrodes antimony, 555 auxiliary, 538, 545 bimetallic, 575... 

The question arises as to which metal is dissolved, and which one is deposited, when combined in an electrochemical cell. The electrochemical series indicates how easily a metal is oxidized or its ions are reduced, i.e., converted into positively charged ions or metal atoms respectively. The standard potential serves for the comparison of different metals. 

Figure 5. Electrochemical series of metals and their standard potentials in volt (measured against NHE).

Each metal or metal area will develop an electrode with a measurable electrical potential. This potential can be referenced to that of a standard hydrogen electrode, which by convention is set at zero. Thus, all metals have either a higher or lower potential compared to hydrogen, and a comparative list of metals can be produced indicating their relative nobility. This list is the galvanic or electrochemical series and measured as an electromotive force (EMF). 

For transmetallations with a metal (metallo-de-metallations, Scheme 10-95) arylmercury compounds are particularly suitable due to the position of mercury as a noble metal in the electrochemical series of standard potentials (for examples see Makarova, 1970). 

We can use the electrochemical series to predict the thermodynamic tendency for a reaction to take place under standard conditions. A cell reaction that is spontaneous under standard conditions (that is, has K > 1) has AG° < 0 and therefore the corresponding cell has E° > 0. The standard emf is positive when ER° > Et that is, when the standard potential for the reduction half-reaction is more positive than that for the oxidation half-reaction. 

Corrosion is the unwanted oxidation of a metal. It cuts short the lifetimes of steel products such as bridges and automobiles, and replacing corroded metal parts costs billions of dollars a year. Corrosion is an electrochemical process, and the electrochemical series is a source of insight into why corrosion occurs and how to prevent it. 

Predict the spontaneous direction of a redox reaction by using the electrochemical series (Example 12.7). 

Because mercury lies above hydrogen in the electrochemical series, it is not oxidized by hydrogen ions. However, it does react with nitric acid ... 

The range of chemical reactivity of metals is wide, from the inertness of the platinum group to the extreme reactivity of some alkali metals. The order of metal reactivity follows essentially the order of the electrochemical series which is shown in Table 17.4 for the metals commonly deposited by CVD. 

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