Sulfide ion was determined by indirect titration with EDTA. To a solution contai

ID: 788751 • Letter: S

Question

Sulfide ion was determined by indirect titration with EDTA.

To a solution containing 25.00 mL of 0.043 32 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. Then ammonia was added

to the filtrate (which contained excess Cu2) until the blue color of

Cu(NH3)4

2 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.

*****PLEASE SHOW WORK*****************

Alternate solution

Reactions are-

[Cu(ClO4)2](aq) + S2-(aq) = CuS(s)+2(ClO4)-

Cu+2(aq) + EDTA(aq) = Cu-EDTA(aq)

No. of moles of Cu2+that do not from precipitate= Number of moles of EDTA reacting

=C(edta)* V(edta) =(0.03927*12.11)=0.475moles

No. of moles of Cu2+ that do not from precipitate=0.475 milimoles

Total number of moles of Cu2+ ion that

are used in reaction with S-2=25.00*0.04332?=?1.083 moles

Number of moles that react with sulphide ion=?1.083-0.475 =0.608 milimoles

No. of Cu2+ ions=No. of sulphide ions=0.608 milimoles

Concentration os sulphide ion=0.608/25=0.02432 M

[S2-]=0.02430 M

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