Alkaline earth metals Group hydroxides

All oxides (O2 ) and hydroxides (OH-) are insoluble except those of allkali metals and certain alkaline earth metals (Group DA Ca, Sr, Ba, Ra). Ca(OH)2 is moderately soluble. 

Like a strong acid, a strong base dissociates completely into ions in water. All oxides and hydroxides of the alkali metals—Group 1 (IA)—are strong bases. The oxides and hydroxides of the alkaline earth metals—Group 2 (IIA)—below beryllium are also strong bases. 

Classically, a base is a substance capable of liberating hydroxide ions, OH , in water solution. Hydroxides of the alkali metals (Group lA) and alkaline earth metals (Group 2A),suchasLiOH, NaOH, KOH, Ca(OH)2,and Ba(OH)2,are the most common inorganic bases. Water solutions of bases are cdlled alkaline solutions or basic solutions. Some of the characteristic properties commonly associated with bases include the following ... 

There are relahvely few common strong bases. The most common soluble strong bases are the ionic hydroxides of the alkali metals (group lA) and the heavier alkaline earth metals (group 2A), such as NaOH, KOH, and C a(OH)2. These compounds completely dissociate into ions in aqueous solution. Thus, a solution labeled 030 M NaOH consists of 0.30 M Na iaq) and 0.30 M OH aq) there is essentially no undisstKiated NaOH. 

The list of strong bases is also fairly short. It consists of the hydroxides of alkali metals (Group lA) and the hydroxides of the heaviest alkaline earth metals (Group 2A). The dissociation of a strong base is, for practical purposes, complete. Equations representing dissociations of die strong bases are as follows ... 

Strontium [7440-24-6] Sr, is in Group 2 (IIA) of the Periodic Table, between calcium and barium. These three elements are called alkaline-earth metals because the chemical properties of the oxides fall between the hydroxides of alkaU metals, ie, sodium and potassium, and the oxides of earth metals, ie, magnesium, aluminum, and iron. Strontium was identified in the 1790s (1). The metal was first produced in 1808 in the form of a mercury amalgam. A few grams of the metal was produced in 1860—1861 by electrolysis of strontium chloride [10476-85-4]. 

Hydrogen can be prepared by the reaction of water or dilute acids on electropositive metals such as the alkali metals, alkaline earth metals, the metals of Groups 3, 4 and the lanthanoids. The reaction can be explosively violent. Convenient laboratory methods employ sodium amalgam or calcium with water, or zinc with hydrochloric acid. The reaction of aluminium or ferrosilicon with aqueous sodium hydroxide has also been used. For small-scale preparations the hydrolysis of metal hydrides is convenient, and this generates twice the amount of hydrogen as contained in the hydride, e.g. ... 

The free alkaloid occurs as Icvorotatory. odorless, while, needle-like crystals pos es.sing a bitter taste. It is almost insoluble in water (1 5.000. 1 1.100 at the boiling point), etha (1 6,250). or chloroform (1 1.220). It is somewhat more soluble in ethyl alcohol (1 210. 1 98 at boiling point). (Note that in this chapter, a solubility of 1 5.000 indicates that I g is soluble in 5.000 mL of the solvent at 2S°C. Soliibilitieca other tcmperatuies are so indicated.) Because of the phenolic hydroxyl group, it is readily soluble in solutions of alkali a alkaline earth metal hydroxides. 

Fig. 6. Mean OH stretching frequencies vOH (average of the various unit-cell group modes) of hydroxide ions which do not donate OH- X hydrogen bonds of alkali and alkaline earth metal hydroxides ( ), and on surfaces of solid oxides as A1203 etc. (O) vs mean M-O distances rM Q of the first OMx coordination sphere [22,86] (3556 cm"l, free ion value [1])...

The most commonly used strong base in the laboratory is sodium hydroxide. It is cheap and soluble. (In fact, all of the alkali metal hydroxides are soluble.) The most commonly used weak base is aqueous ammonia solution, which is sometimes erroneously called ammonium hydroxide there is no evidence that the species NH4OH actually exists. All of the Group 2A elements form hydroxides of the type M(OH)2, where M denotes an alkaline earth metal. Of these hydroxides, only Ba(OH)2 is soluble. Magnesium and calcium hydroxides are used in medicine and industry. Hydroxides of other metals, such as Al(OH)3 and Zn(OH)2 are insoluble and are less commonly used. 

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. 

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