Chap. I] EXPLANATIONS AND DEFINITIONS 7 



cule of hydrochloric acid to give one molecule of water and one 

 molecule of sodium chloride. 



Oxide. — An oxide is a compound in which another element 

 is in combination with oxygen, as water (H2O), carbon dioxide 

 (CO2), sulphur dioxide (SO2), and iron oxide (Fe203). 



Acid oxide. — -An acid oxide (or acid anhydride) is an oxide 

 of a non-metal which in combination with water will form an 

 acid, as carbon dioxide and sulphur dioxide, as shown in the 

 following : — 



CO2 + H2O -> H2CO3 (carbonic acid), 

 SO3 + H2O -> H2SO4 (sulphuric acid). 



Basic oxide. — A basic oxide (or basic anhydride) is an oxide 

 of a metal which in combination with water will give a base, 

 as calcium oxide (CaO) and sodium oxide (Na20), shown in the 

 following : — . 



CaO + H2O -^ Ca(0H)2 (calcium hydroxide), 

 NaoO + H2O -> 2 NaOH (sodium hydroxide). 



Acid. — An acid is a substance which contains hydrogen and 

 an acid radical. The acid radical must contain a non-metal and 

 may contain ox;y'gen. Examples are hydrochloric acid (HCl), 

 sulphuric acid (H2SO4), carbonic acid (H2CO3), hydrobromic acid 

 (HBr), nitric acid (HNO3). 



Base. — A base is a substance which contains a metal and the 

 hydroxyl (OH) radical. Examples are sodium hydroxide (NaOH) 

 and calcium hydroxide (Ca(0H)2). One exception to this is 

 ammonium hydroxide (NH4OH), which contains the ammonium 

 radical (NH4) instead of a metal. 



The alkalies are the bases of sodium, potassium, and ammonium ; 

 they give very strong basic action. 



Both acids and bases give distinctive characteristic actions. 



Salt. — A salt is a substance containing the metal from a base 

 and the acid radical from an acid. Salts may be obtained by the 

 neutralization of an acid by a base, the characteristic hydrogen of 

 the acid combining with the characteristic hydroxyl of the base 

 to form water, leaving the salt as shown in the following : — 



Base + Acid —> Water + Salt 



NaOH +HC1 ^H20 + NaCl (sodium chloride), 



Ca(0H)2 + H2SO4 -^ 2 H2O + CaS04 (calcium sulphate). 



