vity/Student Guide Big Idea Assessments A certain brand of zinc cold medicine is marketed as containing 5.0 mg of zinc in every lozenge. A student team decides to test this claim with a complexometric titration. Xylenol orange forms a red complex with zinc ions, but is yellow when it is free. EDTA is able to form much stronger complexes with zinc ions. For their analysis, the students dissolve one colorless lozenge in a small amount of buffer. They add a few drops of the xylenol orange indicator, then titrate with EDTA. The end point is achieved with 19.36 mL of EDTA. 1. How do the students know when the end point is achieved? Describe what happens to the substances involved in the reaction when the end point is achieved. Explain any observations that may be noted by the students. 2. What concentration of EDTA should the students use so that approximately 25 mL of titrant would be needed to reach the end point if the lozenge contained the 5.0 mg of zinc claimed by the manufacturer? 3. After performing the titration, the students realize that they did not first standardize their EDTA. They perform a standardization of the EDTA titrant solution against 10.00 mL of a 0.500-g/L zinc standard. A total volume of 26.23 mL of EDTA is required to reach the end point. According to the team's data, what is the concentration of zinc in the lozenge? List the equipment the students would need to perform this experiment.

Fundamentals Of Analytical Chemistry

9th Edition

ISBN:9781285640686

Author:Skoog

Publisher:Skoog

Chapter21: Potentiometry

Section: Chapter Questions

Problem 21.25QAP

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Transcribed Image Text:vity/Student Guide Big Idea Assessments A certain brand of zinc cold medicine is marketed as containing 5.0 mg of zinc in every lozenge. A student team decides to test this claim with a complexometric titration. Xylenol orange forms a red complex with zinc ions, but is yellow when it is free. EDTA is able to form much stronger complexes with zinc ions. For their analysis, the students dissolve one colorless lozenge in a small amount of buffer. They add a few drops of the xylenol orange indicator, then titrate with EDTA. The end point is achieved with 19.36 mL of EDTA. 1. How do the students know when the end point is achieved? Describe what happens to the substances involved in the reaction when the end point is achieved. Explain any observations that may be noted by the students. 2. What concentration of EDTA should the students use so that approximately 25 mL of titrant would be needed to reach the end point if the lozenge contained the 5.0 mg of zinc claimed by the manufacturer? 3. After performing the titration, the students realize that they did not first standardize their EDTA. They perform a standardization of the EDTA titrant solution against 10.00 mL of a 0.500-g/L zinc standard. A total volume of 26.23 mL of EDTA is required to reach the end point. According to the team's data, what is the concentration of zinc in the lozenge? List the equipment the students would need to perform this experiment.

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