168 SMITH'S INTERMEDIATE CHEMISTRY 



erties. (1) The solution has an acrid taste, like soap or borax. 

 (2) It changes the color of litmus, reddened by a trace of an acid, 

 back again from red to blue. (3) It is a conductor of electricity, 

 and is decomposed by the current, oxygen being liberated at the 

 positive wire. 



In the following chapter we shall see that these three proper- 

 ties of sodium hydroxide in aqueous solution are properties com- 

 mon to all substances called alkalies. The reader should at this 

 point refer back to p. 131, and contrast these properties with 

 those exhibited by acids. 



Sodium hydroxide in solution enters into double decomposition 

 with many substances. Frequently one of the products is in- 

 soluble, and appears as a precipitate. For example, with a solu- 

 tion of cupric chloride, sodium hydroxide gives a precipitate of 

 cupric hydroxide. 



Skeleton: NaOH + CuCl 2 - Cu(OH) 2 J, + NaCl. 



Balanced: 2NaOH + CuCl 2 -> Cu(OH) 2 J, + 2NaCL 



As this equation shows, sodium hydroxide behaves in such actions 

 as if composed of two parts, namely (Na) and (OH) (compare p. 

 132). The reaction consists, essentially, of a transfer of (OH) 

 groups from (Na) to (Cu). 



Alkalies and Bases. It will be seen that the chemical proper- 

 ties of sodium hydroxide solution may be summed up by saying 

 that it is an alkali. 



Solutions of the alkalies also act upon animal matter, e.g. wool 

 (p. 1), especially when hot, converting it largely into soluble 

 substances. For this reason they are called caustic alkalies. 

 They likewise act slowly upon the components of glass. For 

 this reason a precipitate is often visible in the caustic soda reagent 

 bottle, and the inner surface of the glass is always etched. 



A very delicate lest for an alkali is given by phenolphthakin, 

 a colorless organic substance. One drop of phenolphthalein 



