A 7.13 g sample of an ant-control preparation was decomposed by wet-ashing with H₂SO and HNO₂. The As in the residue was reduced to the trivalent state with hydrazine. After removal of the excess reducing agent, the As(III) required 31.46 mL titration with 0.03142 M 1₂ in a faintly alkaline medium. What is the % As in the original sample? Select one: 1.20% 2.08% 1.04% 0.519%

A 7.13 g sample of an ant-control preparation was decomposed by wet-ashing with H₂SO and HNO₂. The As in the residue was reduced to the trivalent state with hydrazine. After removal of the excess reducing agent, the As(III) required 31.46 mL titration with 0.03142 M 1₂ in a faintly alkaline medium. What is the % As in the original sample? Select one: 1.20% 2.08% 1.04% 0.519%

Fundamentals Of Analytical Chemistry

9th Edition

ISBN:9781285640686

Author:Skoog

Publisher:Skoog

Chapter13: Titrations In Analytical Chemistry

Section: Chapter Questions

Problem 13.27QAP

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A 0.9352g sample of ore containing Fe³+, Al³+ and Sr²+ was dissolved and made up to 500.00 mL. The analysis of metals was performed using complexation volumetry. Initially, an aliquot of 50.00 mL had its pH adjusted to 1.0 and titrated with a standard 0.03145 mol/L EDTA solution, requiring 6.95 mL to reach the end point. Subsequently, another 25.00 mL aliquot was buffered at pH=5 and titrated with the same EDTA solution, requiring 6.24 mL to reach the end point. Finally, a third aliquot of 25.00 mL was titrated at pH=11, requiring 11.10 mL of the same EDTA solution to complete the titration. Given the molar masses: Fe=55.845 g/mol; Al-26.982 g/mol and Sr-87.620 g/mol. a) Determine the percentage of each of the metals in the sample. b) Explain why the change in pH allows the determination of the three ions in this sample.
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