The sulfur content of insoluble sulfides that do not readily dissolve in acid can be measured by oxidation with Br2 to SO2-4.25 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 20°C and 2h at 50°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 0.01463 M BaCl2 were added to precipitate all sulfate as BaSO4. After the addition of 1.000 mL of 0.01000 M ZnCl2 and 3 mL of ammonia buffer, pH 10, the excess Ba2+ and Zn2+ required 2.39 mL of 0.00963 M EDTA to reach the Calmagite end point. Find the weight percent of sulfur in the sphalerite. What is the theoretical value?