18 



PRACTICE 8. 



DETERMINATION OF NITROGEN IN REAGENTS. 



Measure out exactly 10 cc. of the concentrated alkali in a beaker and 

 dilute to 200 cc. with distilled water. Stir and add slowly (finally drop by 

 drop) concentrated sulfuric acid until the alkali is neutralized, as shown 

 by the change of color. 



10 cc. alkali are equivalent to cc. H 2 SO 4 



How many cc. of alkali are necessary to neutralize 20 cc. H 8 SO 4 ? 



Place approximately 2 grams of pure sugar in a Kjeldahl flask, add by 

 measure approximately .650 gm. metallic mercury and 20 cc. sulfuric acid. 

 Digest in a ventilated hood over a low flame till colorless, add carefully, 

 while still boiling hot, powdered potassium permanganate until the solution 

 is green. Allow to cool. Transfer with 200 cc. of ammonia-free water to 

 a copper flask by means of a large funnel supported on an iron ring. Add 

 carefully sufficient concentrated alkali to neutralize 20 cc. of concentrated 

 sulfuric acid, connect with the condenser, shake until thoroughly mixed, 

 and distill as usual. 



Titrations (1) cc. NH 3 



(2) cc. NHa 



Average cc. NH 8 



Check up the standard ammonia solution by titrating against the stand- 

 ard hydrochloric acid solution. 



Correction for nitrogen in reagents in terms of standard ammonia so- 

 lution cc. 



Explain the use of the sugar. Give the reaction between the sugar and 

 the sulfuric acid. Why is the mercury used? the potassium permanganate? 

 the potassium sulfid? 



