Alkaline earth metal hydroxides amphoterism

We have seen that the alkali and alkaline earth metal hydroxides [except Be(OH)2l are basic in properties. The following hydroxides are amphoteric Be(OH)2, Al(OH)3, Sn(OH)2, Pb(OH)2, Cr(OH)3, Cu(OH)2, Zn(OH)2, and Cd(OH)2. For example, aluminum hydroxide reacts with both acids and bases ... 

We have seen that the alkali and alkaline earth metal hydroxides [except Be(OH)2] are basic in properties. The following hydroxides are amphoteric Be(OH)2, Al(OH)3,... 

Compounds M(OH) range from the strongly basic compounds of the alkali and alkaline-earth metals through the so-called amphoteric hydroxides of Be, Zn, Al, etc. and the hydroxides of transition metals to the hydroxy-acids formed by non-metals (B(OH)3) or semi-metals (Te(OH)6). The latter are few in number and are included in other chapters. 

Except for Be, all the alkaline earth metals are oxidized to oxides in air. The IIA oxides (except BeO) are basic and react with water to give hydroxides. Beryllium hydroxide, Be(OH)2, is quite insoluble in water and is amphoteric. Magnesium hydroxide, Mg(OH)2, is only slightly soluble in water. The hydroxides of Ca, Sr, and Ba are strong bases. 

Magnesium is a typical alkaline earth metal in that its hydroxide is a strong base. [The only alkaline earth hydroxide that is not a strong base is Be(OH)2, which is amphoteric.]... 

The alkaline earth metals are somewhat less reactive than the alkali metals. They almost always have an oxidation number of +2 in their compounds. The properties of the alkaline earth elements become increasingly metallic from top to bottom in their periodic group. Aluminum does not react with water due to the formation of a protective oxide its hydroxide is amphoteric. 

Hydroxides M(OH) comprise a numerous class of compounds ranging from strongly basic hydroxides of alkaline metals and alkaline earths, to the so-called amphoteric hydroxides (of beryllium, aluminium, zinc and others) and the hydroxides of transition metals, and further to hydroxo-acids formed by non-metals or semi-metals. 

It is found that only alkali and alkaline earth hydroxides can promote the reaction that is, acidic and amphoteric oxides are inactive for the production of acrylonitrile. The best performances are obtained with silica-supported hydroxides of Cs, Rb, and K. The activity for the formation of acrylonitrile decreases in the order of Cs = Rb = K > Na > Li, and Ba > Ca Mg. This indicates that the activity is related to the electronegativity (basic property) of metal ions corresponding to the hydroxides supported on silica. 

Since lead is amphoteric, in stronger base the Pb2+ ions will exist as soluble plumbite ion, from which it can be electrodeposited [50]. Not all metal contaminants can be electrodeposited from aqueous solution but most precipitate as hydroxides (exceptions are alkali metals, some alkaline earths, NH4 ). Hydrogen ion, meeting the upstream base, reacts exothermically producing nonconducting, molecular water. 

As we noted in Section 22.1, a second-period element is often considerably different from the other elements in its column. Those differences become more pronounced as you progress to the right in the periodic table. We briefly noted differences in properties of lithium from those of the other alkali metals, though those differences are not great. Beryllium, however, shows rather marked differences from the other alkaline earth elements. We have already noted that beryUium differs in its lack of reactivity compared with the other Group IIA metals. Another notable diffoence is in the properties of the hydroxides. Whereas those of the elements magnesium to barium are basic, beryllium hydroxide is amphoteric, reacting with both acids and bases. 

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