COMPOUNDS MIXTURES VALENCE, ETC. 23 



Calcium phosphate, Ca 3 "(P04) 2 "', is used as a source 

 of fertilizer. As it is very insoluble in water, in order to 

 make it soluble and thereby quickly available as a plant 

 food, it is treated with sulphuric acid, which changes the 

 phosphate into a more soluble form. The following reac- 

 tions may take place: 



II. Ca 3 (P04) 2 +2H 2 SO4 = CaH 4 (PO 4 )2+2CaSO 4 , 

 III. Ca 3 (P0 4 ) 2 + H 2 SO 4 = 2CaH (PO 4 ) + CaSO 4 . 



These equations should be read and the balancing of them 

 checked. 



