ALUMINIUM 473 



Exercises. 1. Make equations for the following actions: (a) 

 aluminium on hydrochloric acid; (b) aluminium on mercuric 

 chloride HgCl 2 ; (c) displacement of manganese from manganese 

 dioxide by aluminium. 



2. How must aluminium hydroxide be ionized so as to behave 

 both as an acid and a base? 



3. Make the equation for heating calcium carbonate with: 

 (a) aluminium hydroxide; (b) aluminium oxide. 



4. Explain why the reaction of solutions of aluminates is alka- 

 line (p. 369) and that of alums is acid. 



5. Make the equation: (a) for the action of sulphuric acid on 

 bauxite, assummg the formula of the latter to be A1 2 O(OH) 4 ; (b) 

 for the formation of potash-alum. 



6. Why is the tarnish on aluminium the oxide, and not the 

 carbonate (as on Zn and Mg)? What qualities in a tarnish enable 

 it to protect the metal from further oxidation (p. 467)? 



7. Make equations for the action of bicarbonate of soda and 

 aluminium sulphate (alum baking powder) when heated. 

 Explain what raises the bread. 



