CHAP, vi THE AMPHOTERIC PRINCIPLE 209 



equation (C n H 2n+1 0) - H + Na = C n H 2n+1 ONa + H, when the alcohol 

 remainder [C^H^+jO]' plays the part of an acid, the feeble kat-ion H 

 being replaced by the strong kat-ion sodium, Na. On the other hand, 

 the hydroxyl-group OH may be replaced by a stronger an-ionic radical, 

 such as a chlorine-ion ; thus [CJ^+^OH' + HC1' = CJS^ +1 C\. + H 2 0. 

 This behaviour of alcohols depends on the presence of the OH radical, 

 and it will readily be seen that other compounds which contain this OH 

 radical will behave analogously. Such OH-compounds are, for example, 

 serin (see p. 33) and all phenols, y yOH (p. 49). Alcohols differ, 

 however, from ordinary hydroxyl-compounds, as they only form alcohol- 

 salts in the absence of water. These alcohol -salts on coming into 

 contact with water dissociate hydrolytically, because water is hydro- 

 "lysed by alcohol-salts. Hydrolysis is explained on p. 256. 



The hydroxyl-compounds of most elements belonging to the middle 

 regions of the periodic system may also play the part of either weak 

 acids or weak bases (Winkelblech). 



Thus, compounds having the constitution R'OH or H'R'OH may 

 react in the following manner : 



1. Form simple kat-ions and an-ions. R'OH interacts with acids 

 according to the scheme 



ROH + H ( + C1') ^ R ( + C1') +H 2 0, 

 and with bases according to the equation 



ROH + OH'( + Na) 2 R0'( + Na) + H 2 0. 



An amphoteric electrolyte of this type will give off either a pre- 

 ponderating amount of OH' or H ions, according as to whether the 

 remainder of the molecule has more basic or more acid properties ; 

 thus 



ROH ^ R + OH' or ROH ^ RO' + H. 



Pluribasic acids such as aluminium hydroxide possess the following 

 anions : 



A1(OH) 3 + !Na + 10H' ^ A1(OH) 2 0' + !Na + 1H 2 

 A1(OH) 3 + 2Na + 20H' ^ A1(OH)0 2 " + 2Na + 2H 2 

 A1(OH) 3 + 3Na + 30H' ^ A1O 3 '" + 3Na + 3H 2 0. 



Salt -formation, in water, is most complete in all pluribasic acids if 

 one equivalent of base is present. With each additional basic radical 

 the salt tends to hydrolyse more and more. The normal hydrate 

 readily passes into the metahydrate AlO'OH. 



2. Split off H and OH' ions, and then change into a non-electrolyte 

 instead of becoming a real salt. This happens, for example, in the 



P 



