Test for Sulphur : the sodium fusion extract is acidified with acetic acid and lead acetate is added to it . A black precipitate of lead sulphide indicates the presence of sulphur . S 2- + Pb 2 + PbS Black
Test for halogens : The sodium fusion extract is acidified with nitric acid and then treated with silver nitrate . A white precipitate , soluble in ammonium hydroxide shows the presence of chlorine , a yellowish ppt . sparingly soluble in ammonium hydroxide shows the presence of bromine , a yellowish ppt . insoluble in ammonium hydroxide shows the presence of iodine .
X - + Ag +
AgX QUANTITIVE ANALYSIS ( Carbon and Hydrogen )
Let the mass of organic compound be mg . Mass of water and carbon dioxide produced be m1 and m2 g respectively ;
Nitrogen
% of carbon = 12 x m2 x 100 44 x m
% of hydrogen = 2 x m 1 x 100 18 x m
DUMAS METHOD : A known mass of organic compound is heated with excess of CuO in an atmosphere of CO2 , when nitrogen of the organic compound is converted into N2 gas . The volume of N2 thus obtained is converted into STP and the percentage of nitrogen determined by applying the equation :
Volume of Nitrogen at STP = P1V1 x 273
760 x T1 % N = 28 x vol of N2 at STP x 100
22400 x mass of the substance taken