Chemical Reactions Between Copper Sulfate and Ammonium Hydroxide

Introduction

When copper sulfate (CuSO?) and ammonium hydroxide (NH?OH) solutions are mixed, a series of complex chemical reactions take place. These reactions involve the formation and dissolution of precipitates, leading to the production of various copper complexes. This article delves into the details of these reactions and the resulting solutions.

Formation of Copper Hydroxide Precipitate

The first noticeable reaction occurs when a small amount of ammonia is added to a copper sulfate solution. In this scenario, a blue precipitate of copper(II) hydroxide (Cu(OH)?) forms.

Chemical Reaction:
CuSO?(aq) 2NH?OH(aq) → Cu(OH)?(s) (NH?)?SO?(aq)

The ammonia in the solution reacts with the copper ions, causing the formation of the insoluble copper(II) hydroxide precipitate. However, when excess ammonia is added, the precipitate dissolves to form a deep blue complex solution.

Formation of the Copper-Ammonia Complex

As more ammonia is added, the copper(II) hydroxide (Cu(OH)?) precipitate dissolves. This dissolution is a result of the formation of a deep blue complex called tetraamminecopper(II) ion [Cu(NH?)?]2?.

Chemical Reaction:
Cu(OH)?(s) 4NH?OH(aq) → [Cu(NH?)?]2?(aq) 2H?O(l)

Role of Ammonia in the Reaction

The presence of ammonia plays a crucial role in this reaction. Initially, a small amount of ammonia causes a blue precipitate of copper(II) hydroxide to form. As more ammonia is added, the medium becomes more alkaline, causing the copper(II) hydroxide to dissolve and the solution turns deep blue due to the formation of the complex ion [Cu(NH?)?]2?.

Acidity of Copper(II) Sulfate Solution

Copper(II) sulfate solution is slightly acidic. When ammonium hydroxide is added, the solution initially becomes alkaline due to the presence of OH? ions. The pH change is responsible for the formation and dissolution of the precipitates and the complexation of copper(II) ions.

Equations of the Reactions

Reactions can be represented by the following equations:

Unbalanced Equation:
CuSO?(aq) NH?OH(aq) → Cu(OH)?(s) NH??(aq) SO?2?(aq)

Balanced Equation:
CuSO?(aq) 2NH?OH(aq) → Cu(OH)?(s) (NH?)?SO?(aq)

Observations During the Reaction

When a few drops of ammonium hydroxide are added to a copper sulfate solution, a deep blue solution is initially observed. Shaking the mixture converts the copper(II) sulfate into a light blue copper(II) hydroxide precipitate. Further addition of ammonia dissolves the precipitate and forms a dark blue complex solution.

Conclusion: The reactions between copper sulfate and ammonium hydroxide demonstrate the dynamic nature of chemical complexes. The pH of the solution and the amount of ammonia added significantly influence the formation and dissolution of precipitates, leading to the formation of various copper complexes.