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