Design an experiment to determine the concentration of a specific metal ion in a water sample using a combination of gravimetric and titrimetric methods.
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Title: Determination of the Concentration of Metal Ion in a Water Sample through Gravimetric and Titrimetric Analysis
Objective:
To quantitatively determine the concentration of a specific metal ion (e.g., copper ion, Cu2+) present in a water sample using a combination of gravimetric and titrimetric methods.
Materials:
1. Water sample containing the metal ion
2. Appropriate indicator
3. Standard solution of known concentration (e.g., 0.1 M sodium hydroxide, NaOH)
4. Dilute acid (e.g., hydrochloric acid, HCl or sulfuric acid, H2SO4)
5. Analytical balance
6. Burette
7. Pipettes
8. Filtering apparatus
9. Glass container and stirring rod
10. Safety goggles and gloves
Procedure:
Gravimetric Analysis:
1. Start by preparing a known mass of an appropriate precipitating agent for the specific metal ion in the water sample. For instance, for copper ions, you can use sodium carbonate (Na2CO3).
2. Take a known volume of the water sample (e.g., 100 mL) in a glass container and stir it gently.
3. Slowly add the prepared precipitating agent to the water sample while continuously stirring until a white precipitate forms.
4. Once the precipitate has settled, filter the solution using a filtering apparatus.
5. Wash the precipitate with distilled water to remove any impurities and then transfer it to a pre-weighed crucible.
6. Dry the precipitate at a controlled temperature (e.g., 100°C) until a constant mass is achieved.
7. Record the mass of the dried precipitate.
Titrimetric Analysis:
8. Transfer a known volume of the water sample (e.g., 10 mL) to a conical flask, ensuring proper labeling to distinguish it from the gravimetric sample.
9. Add a few drops of an appropriate indicator to the flask. For example, for copper ions, use potassium iodide (KI), and for the endpoint detection, the solution will turn brownish.
10. Titrate the sample with the standard titrant solution (e.g., 0.1 M NaOH) until a color change indicates the endpoint.
11. Record the volume of the titrant used.
Calculations:
12. Calculate the number of moles of the metal ion in the dried precipitate using the mass recorded from the gravimetric analysis.
13. Determine the molar ratio between the metal ion and the precipitating agent used.
14. Use the volume of the titrant solution and its known concentration to calculate the number of moles of the metal ion in the titrimetric sample.
15. Combine the results from steps 12 and 14 to determine the concentration of the metal ion in the original water sample.
Note: Ensure to follow appropriate safety protocols and practices throughout the experiment, such as wearing safety goggles and gloves, working in a well-ventilated area, and properly disposing of chemical waste.
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