Determination of copper in water | | UPV

Summary

This practical lesson demonstrates how to identify the presence of copper in water using a geometric test. The experiment involves reacting copper salts with potassium iodide in an acidic medium, forming a white precipitate of copper iodide. The procedure includes using reagents like ammonium hydroxide, hydrochloric acid, and acetic acid, and titrating the solution with sodium disulphite. The copper concentration is calculated by measuring the free iodine and the titration endpoint, which appears as a milky white color. The final concentration is expressed in grams per liter.

Takeaways

• 🧪 The lesson aims to identify the presence of copper in water using a geometry test.
• 📘 Copper salts in an acidic medium react with potassium iodide to produce copper iodide and free iodine.
• ⚗️ The reaction forms a white precipitate of copper iodide, which is insoluble in acetic acid.
• 🌡️ The experiment uses sodium disulfite and starch as indicators to examine free iodine in the solution.
• 🔬 Materials required include a burette, test tubes, pipette, reagents like ammonium hydroxide, and glacial acetic acid.
• 💧 10 mL of water is transferred into a burette, with excess ammonium hydroxide added to produce a deep blue color.
• 🟢 Potassium iodide is added to the solution until it turns green, followed by glacial acetic acid to dilute the solution.
• 🟡 Sodium disulfite is titrated into the solution until it changes to a yellowish color, indicating the endpoint is near.
• 🔵 A starch solution is added, turning the solution dark blue, and the titration continues until a milky white color appears.
• 📊 Copper concentration in grams per liter is calculated based on the volume of titrant used, its factor, normality, and the sample volume.

Q & A

What is the main objective of the practical lesson?

The objective is to identify the presence of copper in water using a geometry test.

What materials and reactants are required for the experiment?

The materials include a bread stand and clamps, test tube, automatic pipette, distilled water, and samples of water. The reactants include sodium disulphite, ammonium hydroxide, hydrochloric acid, glacial acetic acid, potassium iodide solution, and starch solution.

What is the initial step in the experiment?

The initial step is to take 10 milliliters of water and transfer it to the test setup.

What happens when ammonium hydroxide is added to the solution?

The solution takes on a deep blue color.

Why is potassium iodide added to the solution?

Potassium iodide is added until a greenish color appears, which indicates the presence of copper salts.

What is the role of glacial acetic acid in the experiment?

Glacial acetic acid helps to adjust the medium and allow the reaction to proceed properly.

How is the endpoint of the titration identified?

The endpoint is reached when the solution turns dark blue with the addition of starch solution, and eventually a milky white color appears.

What is the final calculation in the experiment?

The copper concentration is calculated in grams per liter by multiplying the amount of spent disulphite by its factor and normality, then dividing by the sample volume and multiplying by 1000.

What color change signifies the presence of free iodine during titration?

The solution takes on a yellowish color when free iodine is present.

What is the significance of using starch solution in the experiment?

Starch solution is used as an indicator to identify the endpoint, where the solution becomes dark blue, marking the presence of iodine.