Sulfide EDTA titration

T. Daijaa, K. Yamada. N. Sato. T. Fujino, and Y. Waseda, Determination of Sulfur in Metal Sulfides by Bromine Water-CCl4 Oxidative Dissolution and Modified EDTA Titration, Fresenius J. Anal. Chem. 1998,361, 442. 

Zn is determined by direct titration with EDTA with xelenol indicator after iron elimination with acetate ions and copper - with sulfide ions. 

Sulfide ion was determined by indirect titration with EDTA. 

To a solution containing 25.00 mL of 0.043 32 M Cu(C104)2 plus 15 mL of 1 M acetate buffer (pH 4.5) were added 25.00 mL of unknown sulfide solution with vigorous stirring. The CuS precipitate was filtered and washed with hot water. Then ammonia was added to the filtrate (which contained excess Cu2+) until the blue color of Cu(NH3) + was observed. Titration with 0.039 27 M EDTA required 12.11 mL to reach the murexide end point. Calculate the molarity of sulfide in the unknown. 

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