THEORY OF ELECTROLYTIC DISSOCIATION, ETC, 201 



(OH) ions dissolve to give a faint action on litmus, for example, magnesium 

 hydroxide. Just as in the case of acids, the activity of bases is proportional 

 to the degree of ionization. The most active common bases are potassium 

 and sodium hydroxides, called alkalies, and sometimes caustic alkalies. Their 

 solutions are called lyes. The hydroxides of barium, strontium, and calcium 

 are next in activity. Ammonium hydroxide is a rather weak base. The rest 

 are either sparingly soluble or insoluble. 



Salts. The relationship between salts and acids has already been discussed. 

 As a rule, salts ionize to a considerable degree, and do not show as wide a range in 

 the degree as do the acids. Non-metals are never found in the positive ion of salts, 

 except they occur in a composite radical, as NH 4 . Hence we have no such salts 

 as nitrogen carbonate, carbon sulphate, or sulphur phosphate. The ions of salts 

 do not affect litmus, it is only H' and (OH) 7 ions that have an effect. 



Acid salts. These may be acid, neutral, or alkaline to litmus, depending 

 on the mode of ionization. An acid salt of a highly ionizing acid shows an 

 acid reaction in solution, because of the presence of hydrogen ions. For ex- 

 ample, sodium bisulphate acts thus in solution : 



NaHSO 4 ? Na' + HSO/ 

 HSO/ ?H- 4- SO/ 



Acid salts of weak acids, like carbonic, phosphoric, boric, etc., may be neutral 

 or even alkaline, because the remaining hydrogen of the acid does not become 

 ionic. Sodium bicarbonate is neutral to litmus, because it ionizes thus : 



NaHCO 3 ^ Na- + HCO 3 '. 



The ion HCO/ does not furnish sufficient H' ions by further dissociation to 

 affect litmus. 



Basic salts, These are the reverse of acid salts. They are derived from 

 bases containing more than one (OH) group in the molecule, and the union 

 with acids is such that not all of the (OH) groups are replaced by acid radical. 



/Cl 



Thus Mg (OH) 2 can form Mg<f QTT which shows the plan of structure of all 



basic salts. They are, in nearly all cases, insoluble in water and show slight or 

 no action on litmus. 



Hydrolysis of salts. Some salts, which we would expect from their for- 

 mulas, such as normal salts, to have a neutral reaction in solution, show a 

 noticeable acid reaction, while others show an alkaline one. Such salts are 

 related to an acid or to a base of slight dissociating power, and the cause is 

 found in the slight ionization of water, which, though extremely minute, 

 makes itself felt in some cases. The acid reaction of copper sulphate is ex- 

 plained by the following ionic reaction : 



2H 2 :2H' + 2(OH)' 

 Copper hydroxide dissociates very slightly, being in this respect on a par 

 with water. As a consequence, some Cu" and (OH)' ions unite to form 

 molecules of Cu(OH) 2 . The removal of (OH)' ions of water allows more to 

 be formed, and more Cu(OH) 2 results. This process soon comes to a stop, but 

 not before enough H' ions have been produced to give the solution an acid re- 

 action. The molecules of Cu(OH) 2 are not precipitated, but remain in solu- 

 tion. The quantity is too small. 



