102 SMITH'S INTERMEDIATE CHEMISTRY 



Equations for Actions Already Studied. In the prepa- 

 ration of oxygen (p. 15) we used mercuric oxide and got mercury 

 and oxygen: 



Skeleton: HgO - Hg + O 2 . 



Balanced: 2HgO -> 2Hg + O 2 . 



Potassium chlorate has a composition shown by the formula 



KC1O 3 . It gives (p. 29) potassium chloride (KC1) and oxygen 



(0 2 ). 



Skeleton: KC1O 3 -+ KC1 + 2 . 



Balanced: 2KC1O 3 -> 2KC1 + 3O 2 . 



The variety of chemical change, where one substance gives two 

 (or more) substances, decomposition (p. 16), is readily recognized 

 in these equations. 



Substances, like the manganese dioxide (catalytic agent) used 

 here, and the water so often employed as a solvent, when they 

 undergo no chemical change, are omitted from the equation. 



When the water takes part in the action, however, it must, of 

 course, be included. Thus sodium peroxide (Na 2 2 ) and water 

 (H 2 0) interact (p. 31) to give sodium hydroxide and oxygen: 



2Na20 2 + 2H 2 - 4NaOH + O 2 . 



The Preparation of Hydrogen (p. 50) from sodium (Na) and 

 water gives sodium hydroxide (NaOH) and hydrogen (H 2 ) : 



2Na + 2H 2 -* 2NaOH + H 2 . 



When steam is passed over iron (p. 51), we get hydrogen and 

 magnetic oxide of iron (Fe 3 4 ) : 



3Fe + 4H 2 <= Fe 3 4 + 4H 2 . 



The liberation of hydrogen by the action of zinc (Zn) upon 

 sulphuric acid (H 2 S04), where the products (p. 52) are hydrogen 

 and zinc sulphate, is shown thus: 



Zn + H 2 S0 4 -> H 2 + ZnSO 4 . 



