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Chapter 12: Q37P (page 285)

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-鈫�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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Most popular questions from this chapter

Spreadsheet equation for formation of the complexes ML and ML2.Consider the titration of metal M (initial concentration = CM, initial volume = VM) with ligand L (concentration = CL, volume added = VL), which can form 1:1 and 2 : 1 complexes:

M+L饾啅ML尾1=[ML][M][L]M+2L饾啅ML2尾2=[ML2][M][L]2

Let 伪M be the fraction of metal in the form M, 伪ML be the fraction in the form ML, and 伪ML2be the fraction in the form ML2. Following the derivation in Section 12-5, you could show that these fractions are given by

role="math" localid="1667801924683" 伪M1=11+尾1[L]+尾2[L]2伪ML=尾1[L]1+尾1[L]+尾2[L]2伪ML2=尾2[L]21+尾1[L]+尾2[L]2

The concentrations of ML and ML2are

[ML]=伪MLCMVMVM+VL[ML2]=伪ML2CMVMVM+VL

because CMVMVM+VLis the total concentration of all metal in the solution. The mass balance for ligand is

[L]+[ML]+2[ML2]=CMVMVM+VL

By substituting expressions for [ML] and [ML2] into the mass balance, show that the master equation for a titration of metal by ligand is

蠒=CLVLVM+VM=伪ML+2伪ML2+LCM1-LCL

Calculate pCu2+ at each of the following points in the titration of 50.00 mL of 0.001 00 M Cu2+ with 0.00100 M EDTA at pH 11.00 in a solution with [NH3] fixed at 1.00 M:

(a) 0 mL(b) 1.00 mL (c) 45.00 mL (d) 50.00 mL (e) 55.00 mL

Give three circumstances in which an EDTA back titration might be necessary

If back titration required 13.00 mL Zn2+, what was the original concentration of Ni2+?

The sulfur content of insoluble sulfides that do not readily dissolve in acid can be measured by oxidation with Br2 to .25 Metal ions are then replaced with H+ by an ion-exchange column, and sulfate is precipitated as BaSO4 with a known excess of BaCl2. The excess Ba2+ is then titrated with EDTA to determine how much was present. (To make the indicator end point clearer, a small, known quantity of Zn2+ also is added. The EDTA titrates both the Ba2+ and the Zn2+.) Knowing the excess Ba2+, we can calculate how much sulfur was in the original material. To analyze the mineral sphalerite (ZnS, FM 97.46), 5.89 mg of powdered solid were suspended in a mixture of CCl4 and H2O containing 1.5 mmol Br2. After 1 h at 200 C and 2 h at 500 C, the powder dissolved and the solvent and excess Br2 were removed by heating. The residue was dissolved in 3 mL of water and passed through an ion-exchange column to replace Zn2+ with H+. Then 5.000 mL of 0.014 63 M BaCl2 were added to precipitate all sulfate as BaSO4. After the addition of 1.000 mL of 0.010 00 M ZnCl2 and 3 mL of ammonia buffer, pH 10, the excess Ba2+ and Zn2+ required 2.39 mL of 0.009 63 M EDTA to reach the Calmagite end point. Find the weight percent of sulfur in the sphalerite. What is the theoretical value?
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