Sulfide ion was determined by indirect titration with EDTA. To a solution containing 25.00 mL of 0.04332 M Cu(ClO4)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. Ammonia was added to the filtrate (which contained excess Cu2+) until the blue color of Cu(NH3)42+ was observed. Titration of the filtrate with 0.039 27 M EDTA required 12.11 mL to reach the murexide end point. Calculate the molarity of sulfide in the unknown.

Short Answer

Expert verified

The molarity of sulfide in the unknown will be 0.0243M

Step by step solution

01

Given Information

Amount of unknown sulfide (S2- ) solution = 25 mL

Amount of Cu(CIO4)2 added = 25.0 mL of 0.04332 M Cu(CIO4)2

EDTA required for complete titration to reach murexide end point =12.11 mL of 0.03927 M EDTA

02

Determine the amount of S2- reacted

Precipitation reaction

Cu2++S2-CuS(s)

Total amount of Cu2+ used

=(25.00mL)(0.04332MCu(CIO4)2)=1.083mmol

Amount of EDTA reacted= Excess amount of Cu2+ present

Therefore, excess amount of Cu2+

=(12.11mL)(0.03927M)=0.4756mmol

Therefore, the amount of S2- reacted

=(1.083-0.4756)mmol=0.6074mmol

03

Determine the concentration of sulfide in the unknown solution

The number of S2- reacted =0.6074 mmol

Volume of unknown solution taken =25 mL

Therefore, the concentration of sulfide in the unknown will be

=0.6074mmol25.00mL=0.0243M

Therefore, the molarity of sulfide in the unknown will be 0.0243M

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