Question

Write a balanced equation for the reaction of ammonia with (a) \(\mathrm{Cu}^{2+}\) (b) \(\mathrm{H}^{+}\) (c) \(\mathrm{Al}^{3+}\)

Short answer

Question: Write balanced equations for the reactions of ammonia with Cu²⁺, H⁺, and Al³⁺ ions. Answer: 1. Reaction with Copper (II) ion (Cu²⁺): \(\mathrm{Cu}^{2+} + 4\mathrm{NH}_3 \to [\mathrm{Cu}(\mathrm{NH}_3)_4]^{2+}\) 2. Reaction with the Hydrogen ion (H⁺): \(\mathrm{NH}_3 + \mathrm{H}^{+} \to \mathrm{NH}_4^+\) 3. Reaction with Aluminum ion (Al³⁺): \(\mathrm{Al}^{3+} + 6\mathrm{NH}_3 \to [\mathrm{Al}(\mathrm{NH}_3)_6]^{3+}\)

Step-by-step solution

Reaction with Copper (II) ion (Cu²⁺)

Ammonia forms complexes with copper, turning light blue in the presence of ammonia. The general equation is: \(\mathrm{Cu}^{2+} + n\mathrm{NH}_3 \to (\mathrm{Cu}(\mathrm{NH}_3)_n)^{2+}\), where n = 4 (for the tetraammine complex) Balanced Equation: \(\mathrm{Cu}^{2+} + 4\mathrm{NH}_3 \to [\mathrm{Cu}(\mathrm{NH}_3)_4]^{2+}\).

Reaction with the Hydrogen ion (H⁺)

Ammonia is a base and will react with acids to form ammonium salts. The balanced equation for the reaction is: \(\mathrm{NH}_3 + \mathrm{H}^{+} \to \mathrm{NH}_4^+\)

Reaction with Aluminum ion (Al³⁺)

Ammonia forms complexes with aluminum ions, just like in the case of copper ions. The balanced equation for the reaction is: \(\mathrm{Al}^{3+} + 6\mathrm{NH}_3 \to [\mathrm{Al}(\mathrm{NH}_3)_6]^{3+}\)

Key concepts

Copper Ammonia Complex

The interaction between copper ions and ammonia is a classic example of complex ion formation. When ammonia, which acts as a ligand, encounters a copper(II) ion in solution, a copper ammonia complex is formed. The color change to light blue is indicative of the complexation. In chemical terms, the reaction can be represented by the balanced equation:
\[\begin{equation}\mathrm{Cu}^{2+} + 4\mathrm{NH}_3 \rightarrow [\mathrm{Cu}(\mathrm{NH}_3)_4]^{2+}\end{equation}\]
Each copper ion (\( \mathrm{Cu}^{2+} \)) coordinates with four ammonia (\( \mathrm{NH}_3 \)) molecules to form a tetraammine copper(II) complex. In this complex, ammonia serves as a Lewis base, donating its lone pair of electrons to the copper ion, a Lewis acid. This interaction illustrates the fundamental concepts of coordination chemistry and the dynamic behavior of transition metals like copper in aqueous solutions. Understanding this equilibrium is essential for students studying inorganic chemistry, as it demonstrates not only the stoichiometry but also the electron pairing and geometry around metal centers.

Ammonia as a Base

Chemically, ammonia (\( \mathrm{NH}_3 \)) is a weak base because it accepts a proton (\( \mathrm{H}^+ \)) in water to form the ammonium ion (\( \mathrm{NH}_4^+ \)). This proton transfer reaction is an application of the Brønsted-Lowry theory of acids and bases. The balanced chemical equation for this reaction is:
\[\begin{equation}\mathrm{NH}_3 + \mathrm{H}^{+} \rightarrow \mathrm{NH}_4^+\end{equation}\]
This also illustrates the basics of acid-base reactions in aqueous solutions. Ammonia's basicity is a key concept, especially when it comes to understanding its reactions with different species, whether they be metallic ions to form complexes or protons to form ammonium salts. The ability to donate a lone pair of electrons makes ammonia a versatile and widely studied compound in the field of inorganic chemistry.

Ammonium Salts

When ammonia acts as a base and accepts a hydrogen ion, the product is an ammonium ion, which can further react with anions to form various ammonium salts. A simple example is the reaction with hydrochloric acid to form ammonium chloride:
\[\begin{equation}\mathrm{NH}_3 + \mathrm{HCl} \rightarrow \mathrm{NH}_4Cl\end{equation}\]
These salts have a wide range of applications, including use in fertilizers, cleaning agents, and even in medications. The process of forming ammonium salts highlights the importance of understanding stoichiometry and the conservation of charge in chemical reactions. The production of ammonium salts from ammonia is a fundamental reaction that shows the dual role of ammonia as both a compound and a reactant, contributing to the understanding of acid-base chemistry and the practical applications of such reactions.

Aluminum Ammonia Complex

Similar to copper, aluminum ions also form complexes with ammonia. The aluminum ammonia complex forms when aluminum ions in solution (\( \mathrm{Al}^{3+} \)) interact with ammonia molecules. With six ammonia ligands attaching to the central aluminum ion, a hexaamminealuminum(III) complex is created:
\[\begin{equation}\mathrm{Al}^{3+} + 6\mathrm{NH}_3 \rightarrow [\mathrm{Al}(\mathrm{NH}_3)_6]^{3+}\end{equation}\]
This process demonstrates the octet rule and the preference for a central ion to complete its outermost electron shell, resulting in a stable configuration. Understanding the formation of aluminum ammonia complexes is vital in areas where aluminum ions are abundant, such as water treatment processes or the hydrolysis of aluminum-based compounds. The study of such complexes aids in grasping the concept of coordination number and the geometry of complex ions, which is a crucial aspect of coordination chemistry.