Magnesium standard reduction potentials

The trend shown by the standard reduction potentials lor the reductions of sodium, magnesium and aluminium ions to their respective metals... 

Zinc metal is produced by reducing ZnO with coke, and magnesium metal is produced by the electrolysis of molten MgCl2. Look at the standard reduction potentials in Appendix D, and explain why magnesium can t be prepared by the method used for zinc. 

A different way of preventing iron corrosion is to use a sacrificial anode. A comparison of the standard reduction potentials of iron and magnesium... 

The standard reduction potentials are -1.798 for the uranium half-reaction and —2.714 for the magnesium half-reaction, (a) Will this semp work spontaneously (b) Calculate the voltage produced by this cell as written. 

Look up the standard reduction potentials for sodium, magnesium, and aluminum. What do these potentials indicate in terms of their relative strengths as reducing agents Should aluminum liberate hydrogen readily from water Indicate clearly your reasoning. 

Electrolytic methods using molten salts are important for obtaining the more active metals, such as sodium, magnesium, and aluminum. These metals cannot be obtained from aqueous solution because water is more easily reduced than the metal ions. The standard reduction potentials of water under both acidic (B°ed O-OO V) and basic (B°ed —0.83 V) conditions are more positive than those of Na" (B°ed = 2.71 V), Mg (EJj = -2.37 V), and Al +(B°ed = -1.66 V). 

For nearly all metals, oxidation is a thermodynamically favorable process in air at room temperature. When the oxidation process is not inhibited in some way, it can be very destructive. Oxidation can also form an insulating protective oxide layer, however, that prevents further reaction of the underlying metal. On the basis of the standard reduction potential for Al, for example, we would expect aluminum metal to be very readily oxidized. The many aluminum soft-drink and beer cans that litter the environment are ample evidence, however, that aluminum undergoes only very slow chemical corrosion. The exceptional stability of this achve metal in air is due to the formation of a thin protective coat of oxide—a hydrated form of AI2O3—on the surface of the metal. The oxide coat is impermeable to O2 or H2O and so protects the underlying metal from further corrosion. Magnesium metal is similarly protected. Some metal alloys, such as stainless steel, likewise form protective impervious oxide coats. 

Magnesium and its alloys are definitely anodic to the A1 alloys and, thus, contact with aluminum increases the corrosion rate of magnesium. For example, in sodium chloride solutions (3-6%), the potential of Mg alloys is -1.67 V/SHE while that of Al-12%Si and pure aluminum are -0.83 to -0.85, respectively. However, such contact is also likely to be harmful to aluminum, since magnesium may send sufficient current to the aluminum to cause cathodic corrosion in alkaline medium. Aluminum oxide is amphoteric and so it is soluble in acid as well as in alkaline solutions. The standard reduction potentials of these two half-reduction reactions are (-1.66 V/SHE) and (-2.35 V/SHE), respectively. Alkaline reaction of the possible existence of aluminum phase in sacrificial Mg anodes is ... 

Figure 6.15. Magnesium, Mg, is a base metal with a highly negative standard reduction potential in the electrochemical reactivity series. Magnesium is therefore widely used as a sacrificial anode in the corrosion protection of steel. The photo shows preparation of sacrificial anodes - in this case of zinc - to be mounted on offshore steel structures.

Use standard reduction potentials to predict which metal in each of the following pairs is the stronger reducing agent under standard conditions (a) zinc or magnesium (b) sodium or tin. 

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