DECOMPOSITION OF COMPOUNDS. 59 



the characteristic properties of both classes, acids and bases ; of neither 

 class, however, to a very great extent. 



Salts. Salts are acids in which hydrogen has been replaced by 

 metals or by basic radicals; a salt may be formed by the union of an 

 acid and a base (usually with the simultaneous formation of water), 

 or by the action of an acid on a metal (usually with the liberation of 

 hydrogen). 



For instance : 



NaOH -f HNO 3 = NaNO 3 + H 2 O. 

 Sodium Nitric Sodium Water. 



hydroxide. acid. nitrate. 



Fe + H 2 SO 4 = FeSO 4 + H 2 . 



Iron. Sulphuric Ferrous Hydrogen. 



acid. - sulphate. 



The process of combining an acid with a base in such a proportion 

 that the acid and alkaline reactions disappear, and a neutral salt is 

 formed, is known as neutralization. 



According to the number of hydrogen atoms replaced in an acid, 

 we distinguish normal and acid salts. [A normal salt is one formed by 

 the replacement of all the replaceable hydrogen atoms of an acidA 

 For instance: Potassium chloride, KC1, potassium sulphate, K 2 SO 4 , / 

 potassium phosphate, K 3 PO 4 . (As monobasic acids have but one atom 

 of hydrogen which can be replaced, they form normal salts only.) 



Normal salts often have a neutral reaction to litmus, but they may 



have an acid, or even an alkaline reaction. 



7 



Acid salts are acids in which there has been replaced only a portion 

 of their replaceable hydrogen atoms. / For instance: KHSO 4 , 

 K 2 HP0 4 , KH 2 P0 4 



Basic salts are salts containing a higher proportion of a base than 

 is necessary for the formation of a normal salt/ Instances are basic 

 mercuric sulphate, HgSO 4 .(HgO) 2 , basic lead nitrate, Pb(NO 3 ) 2 . 

 Pb(OH) 2 . According to modern views basic salts are looked upon 

 as derived from bases by replacement of part of their hydrogen by acid 

 radicals. In the base lead hydroxide, Pb(OH) 2 , one of the hydrogen 

 atoms may be replaced by the radical of nitric acid, when basic lead 



NO 

 nitrate, Pb rr 3 ' is formed. 



In bismuth hydroxide, Bi(OH) 3 , one, two, or three hydrogen atoms 

 may be replaced by nitric acid, when the salts Bi(^ /QTT\ -^^\OH 



and Bi(NO 3 ) 3 are formed. The first two compounds are basic salts, 

 while the third one is the normal salt. 



