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Using an ion-selective electrode, a student measures the concentration of chloride ions in a solution as 0.20 M. The solution also contains either nitrate or sulfate ions. How can the student determine which ion(s) is present in the solution and calculate their concentration?

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ago by (650 points)
The student can use a series of precipitation reactions to determine which ion s  is present in the solution and calculate their concentration. Here's a step-by-step procedure:1. First, the student should prepare a solution of silver nitrate  AgNO3 , which can react with both chloride  Cl-  and sulfate  SO4 2-  ions to form precipitates. The silver nitrate solution should have a known concentration, for example, 0.20 M.2. Take two separate samples of the original solution containing chloride ions and the unknown ion s . Label them as Sample A and Sample B.3. Add a small volume of the 0.20 M AgNO3 solution to Sample A and observe if a precipitate forms. The possible reactions are:   a  AgNO3 + Cl-  AgCl s  + NO3-   b  2AgNO3 + SO4 2-  Ag2SO4 s  + 2NO3-If a white precipitate forms, it indicates the presence of either chloride or sulfate ions. Since we already know that chloride ions are present, this result is expected.4. Filter the precipitate in Sample A and collect the filtrate. The filtrate should now contain the nitrate ions from the AgNO3 and possibly the sulfate ions if they were present in the original solution.5. Add a small volume of the 0.20 M AgNO3 solution to Sample B and then add a few drops of 6 M nitric acid  HNO3  to dissolve any AgCl precipitate that may form. The nitric acid will react with AgCl to form soluble AgNO3:   AgCl s  + HNO3  AgNO3 aq  + HCl aq 6. Observe if a precipitate forms in Sample B after adding the nitric acid. If a white precipitate forms, it indicates the presence of sulfate ions in the original solution. If no precipitate forms, it indicates the presence of nitrate ions.7. To calculate the concentration of the sulfate or nitrate ions, the student can perform a titration using the 0.20 M AgNO3 solution as the titrant. Record the volume of AgNO3 solution required to reach the endpoint  formation of a precipitate .8. Use the stoichiometry of the reaction and the volume of AgNO3 solution used in the titration to calculate the concentration of the sulfate or nitrate ions in the original solution.For sulfate ions:   2AgNO3 + SO4 2-  Ag2SO4 s  + 2NO3-   moles of AgNO3 = 2 * moles of SO4 2-For nitrate ions:   AgNO3 + Cl-  AgCl s  + NO3-   moles of AgNO3 = moles of Cl- + moles of NO3-By following these steps, the student can determine which ion s  is present in the solution and calculate their concentration.

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