202 NON-METALS AND THEIR COMBINATIONS. 



The ionic equation for sodium carbonate which shows marked alkaline reac- 



Na 2 C0 3 ; 2Na' + CO/ 1 _^ HCQ , 

 H 2 ; (OH)' + H ; . /."* 



Here a small quantity of (OH) 7 ions are produced, which give the solution an 

 alkaline reaction. This action of water on salts is called hydrolysis. The 

 changes are usually represented by the simpler reactions : 



CuS0 4 + 2H 2 = Cu(OH), + H 2 S0 4 

 Na 2 C0 3 + H 2 = NaOH + NaHCO. 



Soap always shows an alkaline reaction, which is due to hydrolysis. Salts 

 containing bivalent or trivalent radicals, metallic or acid, are more prone to 

 undergo hydrolysis than those containing univalent radicals only. 



Neutralization. Broadly speaking, the replacement of hydrogen of an acid 

 by metal is neutralization, but, as shown in the preceding paragraph, certain 

 salts have an acid or alkaline reaction in solution, and consequently it is 

 impossible in such instances to produce an exactly neutral solution by bring- 

 ing the acid and base together in the proportions to form the salt. A great 

 many salts, however, are neutral, and in these cases it is possible to bring 

 together the corresponding acids and bases, and have complete reactions and 

 neutral solutions. In the more restricted sense neutralization refers to such 

 complete reactions. They can be employed for quantitative determinations 

 of the acids or bases in solutions. This subject is treated under Acidimetry 

 and Alkalimetry in the section on Volumetric Analysis. 



Neutralization is an example of double decomposition and of a complete 

 reaction. The interpretation of this is found in the ionic theory. In the 

 beginning before mixing, there are H* ions which have an acid reaction, and 

 (OH)' ions which are alkaline. When they are brought together by mixing 

 the acid and base and the neutral point is established, both H* and (OH)' ions 

 disappear, as is proved experimentally by conductivity tests. This disappear- 

 ance results from the fact that water is practically undissociated. and, there- 

 fore, these ions cannot exist in the same solution, but unite to form molecules 

 of water. Of course, the metal ions and acid radical ions also unite to some 

 extent to form molecules, but if the solutions are quite dilute the proportion 

 of undissociated molecules is negligible. 



The ionic equation for the neutralization of sodium hydroxide and nitric 

 acid serves as a type for all instances : 



NaOH ^ Na' + (OH)') 

 HN0 3 ; NO./ + H- / " 



It' 

 NaNO 3 



As fast as H' and (OH)' unite more. NaOH and HNO 3 dissociate, until finally 

 all is dissociated, and only ions of sodium nitrate and some undissociated mole- 

 cules of the same are left in the solution at the point of neutrality. 

 The essential reaction may be shown in the simplified equation : 



Na- + (OH)' + H- + N0 3 ' = Na' + NO 3 ' -f H 2 O, 



or by the following still simpler equation, which expresses the fact that neu- 

 tralization is a reaction between H- and (OH)' ions : 



