66 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Detection of Water in Absolute Alcohol. 



(a) If the alcohol contains a considerable quantity of water its 

 presence will be shown by adding some anhydrous copper sulphate 

 which turns blue. 1 



(ff) 0-5 per cent, of water may be detected by adding a crystal of 

 potassium permanganate ; the liquid will assume a pink colour. 



(r) Traces of water in absolute alcohol according to Yvon may be 

 detected by means of calcium carbide. If water be present, bubbles 

 of acetylene are given off and the liquid becomes milky, due to the 

 formation of calcium hydroxide. 



Reactions. 



1. Action of Sodium. 



On adding about I gm. of sodium to 20 c.c. of absolute alcohol in 

 a small flask there is an evolution of hydrogen just as with water, but 

 the reaction is by no means so violent. The gas which is evolved may 

 be collected in an inverted test tube and shown to be hydrogen by 

 burning. 



When the sodium has dissolved the solution is evaporated to dry- 

 ness on the water-bath. A white solid sodium ethoxide remains, 

 which is very hygroscopic and is decomposed by water, yielding 

 alcohol which can be recognised by its smell and by the iodoform 

 test : 



C 2 H 5 OH + Na = C 2 H 5 ONa + H 

 C 2 H 5 ONa + H 2 O = C 2 H 5 OH + NaOH. 



This reaction shows that one of the hydrogen atoms in alcohol is 

 replaceable by sodium. 



2. Action of Phosphorus Pentachloride. 



On adding a little phosphorus pentachloride to a small quantity 

 of alcohol, a vigorous action occurs and hydrochloric acid fumes are 

 evolved. Ethyl chloride and phosphorus oxychloride are the other 

 products. The smell of ethyl chloride will be noticed when the 

 hydrochloric acid fumes cease to be given off. This reaction shows 

 the presence of an hydroxyl or OH group : 



C 2 H B OH + PC1 5 = C 2 H 5 C1 + POC1 3 + HC1. 



1 Prepared by gently heating a crystal of copper sulphate in a crucible until it falls to 

 powder. 



