ACIDS, ALKALIES, AND SALTS 139 



part of the hydrogen only part of the hydrogen is replaced 

 by the metal. 



To illustrate: When sulphuric acid and sodium hydrate (NaOH) 

 are mixed, the first action is as follows: 



H 2 S0 4 + NaOH HNaS0 4 + H 2 



Sulphuric Sodium Acid Sodium Water 



Acid Hydrate Sulphate 



The second step in the change is: 



HNaS0 4 + NaOH = Na 2 SO 4 + H 2 



If excess sulphuric acid is used, NaOH may be formed immediately. 

 The salt formed at first is called an add salt. If all the hydrogen 

 were replaced it would be called a normal salt. Normal salts have 

 no effect on blue or red litmus paper. 



One of the principal sodium salts is sodium carbonate, 

 often caned soda ash, and is represented by the formula 

 Na 2 C0 3 . 



Soda crystals, or sal soda, are made by dissolving soda ash in 

 hot water, and allowing the clear liquid to cool. Crystals then form, 

 having the composition of Na 2 C0 3 .10H 2 0. Soda crystals contain 

 over 60% of water, do not dissolve as readily as does soda ash, and 

 are, therefore, not economical to buy. 



149. The Formation of Alkalies. Alkali is the commer- 

 cial arid industrial name for a strong base, such as caustic soda 

 (NaOH), caustic potash (KOH), and ammonium hydroxide 

 (NH 4 OH). An alkali is opposite to an acid in character 

 and turns red litmus paper blue. When a limited amount 

 of acid is added to an excess of alkali, only part of the OH 

 (hydroxide radical) is replaced by a negative element or 

 radical, and a basic salt is formed. 



