Test of Cu2+ | Chemistry for JAMB PDF Download

Introduction

The test for Cu²⁺ ions involves several chemical reactions that help to identify the presence of copper(II) ions in a given solution. Copper is a transition metal with various applications, and its detection is important in various fields, including analytical chemistry, environmental science, and metallurgy.

Materials

• Test solution (unknown solution containing Cu²⁺ ions)
• Sodium hydroxide (NaOH) solution
• Ammonium hydroxide (NH₄OH) solution
• Hydrochloric acid (HCl) solution
• Dilute sulfuric acid (H₂SO₄) solution
• Sodium carbonate (Na₂CO₃) solution
• Filter paper
• Bunsen burner or heating source
• Glass rod
• Test tubes
• Dropper

Procedure

• Take the test solution (unknown solution containing Cu²⁺ ions) in a test tube.
• Add a few drops of sodium hydroxide (NaOH) solution to the test solution.
  Observation: A light blue precipitate of copper(II) hydroxide (Cu(OH)₂) indicates the presence of Cu²⁺ ions.
• To confirm the presence of Cu²⁺ ions, add excess ammonium hydroxide (NH₄OH) solution dropwise to the mixture.
  Observation: The light blue precipitate dissolves in excess NH₄OH, forming a deep blue solution of tetraamminecopper(II) complex [Cu(NH₃)₄]²⁺.
• To further confirm the presence of Cu²⁺ ions, carefully add dilute sulfuric acid (H₂SO₄) to the solution obtained in step 3.
  Observation: A pale blue precipitate of copper(II) sulfate (CuSO₄) confirms the presence of Cu²⁺ ions.
• To differentiate Cu²⁺ ions from other metal ions, perform a flame test.
• Procedure: Dip a clean nichrome wire loop into the Cu²⁺ solution and heat it in the hottest part of a Bunsen burner flame.
  Observation: The flame turns green due to the characteristic green color produced by copper(II) ions.
• Optional confirmation test: To further validate the presence of Cu²⁺ ions, add sodium carbonate (Na₂CO₃) solution to the test solution.
  Observation: A blue precipitate of copper(II) carbonate (CuCO₃) confirms the presence of Cu²⁺ ions.

Conclusion

The test for Cu²⁺ ions involves the formation of a light blue precipitate with sodium hydroxide, its dissolution with excess ammonium hydroxide, and the subsequent precipitation of copper(II) sulfate with dilute sulfuric acid. The flame test further confirms the presence of Cu²⁺ ions by producing a characteristic green color. Adding sodium carbonate solution can be used as an optional confirmation test, yielding a blue precipitate of copper(II) carbonate. These reactions collectively allow for the identification of copper(II) ions in a given solution.