Standard electrode potential magnesium

Metals having an electronegative potential show a tendency to oxidise and thus to corrode in aqueous media, if the conditions allow. This tendency increases as the potential becomes more electronegative. It is well known that magnesium (standard electrode potential, —2380 mV) degrades much more under the effect of moisture than lead (standard electrode potential, — 126 mV). 

The standard electrode potential of magnesium is given, along with the potentials of other metals, in Table 4.17 and the steady-state potentials of magnesium in various solutions are listed in Table 4.18. ... 

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. 

Beryllium has a standard electrode potential less negative than magnesium the anomalous behaviour of lithium in this respect is not repeated by beryllium, even though Be + hydrates strongly. But, unlike K, Rb+ and Cs+, all these bipositive cations are hydrated. 

Though the first and second ionisation potentials of Mn are similar to those of Mg, the standard electrode potential Mn /Mn is much less negative than that for magnesium because of the much greater heat of sublimation. 

Metals differ greatly in how easily they are oxidized. The most reactive metals are those with a very negative standard electrode potential. Of the commonly used metals, the alkali metals lithium, sodium, and potassium are highly reactive the next most reactive is magnesium, then zinc. 

Galvanized steel is a common example of galvanic coupling where steel (Fe), with a standard electrode potential of —0.440 V vs. SHE, is cathodicaUy protected by zinc, which has a more active standard electrode potential of —0.763 V. Obviously, zinc is not a corrosion-resistant metal and cannot be classified as a barrier coating. It protects steel from corrosion through its sacrificial properties. Because zinc is less noble than iron in terms of the standard electrode potentials, it acts as an anode. The sacrificial anode (zinc) is continuously consumed by anodic dissolution reaction and protects the underlying metal (iron in steel) from corrosion. In practice, sacrificial anodes are comprised of zinc, magnesium alloys, or aluminum. 

Magnesium is a divalent metal and is silvery white in appearance. It is the eighth most abundant element and sixth most abundant metal. The atomic weight is 24-32 and the specific gravity of the pure metal 1 -738 at 20°C. The structure is close packed hexagonal. The melting point is 6S0°C and the boiling point 1 I07°C. The sp ific heat at 20 C is 1 -030 kJ/kg "C and the thermal conductivity at 20°C is 157- 5 W/m C the electrochemical equivalent is 0-126 mg/C. The standard electrode potential = -2-37 V, but in... 

Magnesium has the lowest standard potential of all the engineering metals, as is illustrated in Fig. 4-3. At 25 °C magnesium (Mg VMg) has a standard electrode potential of-2.37 Vnhe (Shreir, 1965 Chapter XX... 

---