16 WATER 



Washing soda: 



Ca(HC03)2 + NaoCOa = CaCOg + 2NaHC03 

 CaS04 + NagCOs = CaCOg + Na2S04 



Phosphates : 



3Ca(HC03)2 + 2Na3P04 = Ca3(P04)2 + GNaHCOa 

 3CaS04 + 2Na3P04 = Ca3(P04)2 + 3Na2S04 



The use of various water-softening materials in the kitchen and laundry 

 of the average household is not a very satisfactory procedure. In most 

 cases little or no softening of the water, and consequent saving of soap, 

 is effected. At best it is a temporary expedient and to a large extent means 

 waste of money. A satisfactory method of softening water is by means 

 of a zeolite. Silicates of this character are sold under such trade names 

 as Permutit, Refinite, and Bormite. Water treated in this way is soft. 

 In fact, it requires less soap than distilled water because of the presence 

 of a small amount of sodium bicarbonate. The softening of water by 

 means of a silicate may be represented by the following equation: 



Ca(HC03)2 + NaoO-Alo03-2Si02-6H20 = 

 CaO-Al203-2Si02-6H20 + 2NaHC03 



After a time the silicate will have taken up all the calcium or magnesium 

 that it will hold and must then be regenerated if the water is to be softened. 

 This is done by means of a strong solution of salt that displaces the 

 absorbed calcium or magnesium and again forms the sodium silicate. 

 This operation is called the regeneration of the silicate and is indicated 

 by the following equation: 



CaO'Al203-2Si02-6H20 + 2NaCl = Na20-Alo03-2Si02-6H20 + CaClg 



A more recent method for softening water is by means of cation exchange 

 resins. Such resins are extremely insoluble, high polymer organic com- 

 pounds that contain many acidic groups, e.g., sulfonic, — SO3H; carboxyl, 

 — COOH; etc. A phenol sulfonic acid resin is made by polymerizing 

 m-phenol sulfonic acid, C6H4 (OH) SO3H, and formaldehyde. Commercial 

 products of this type are Amberlite IR-100 and Dowex-50. The removal 

 of a cation such as Ca + + from water by the resin may be represented 

 by the following equation: 



Ca(HC03)o or CaS04 + 2NaR = CaRs + 2NaHC03 or Na2S04 



In the above equation NaR represents the sodium form of the ion exchange 

 resin. Similar equations can be set up to show the removal of magnesium, 

 iron, and other cations. When the resin becomes loaded with cations, it 

 is regenerated by washing with sodium chloride brine. The reaction is 

 illustrated by the equation 



CaR. + 2NaCl = 2NaR + CaCIg 



