Question

Consider the following reaction: \(\mathrm{HCHO}+2\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}+3 \mathrm{OH}^{-} \rightarrow 2 \mathrm{Ag}+\mathrm{HCOO}^{-}\) \(+4 \mathrm{NH}_{3}+2 \mathrm{H}_{2} \mathrm{O}\)

Short answer

The reaction is already properly balanced as provided, with 1 molecule of formaldehyde reacting with 2 silver ammonia complexes and 3 hydroxide ions, producing 2 silver atoms, 1 formate ion, 4 ammonia molecules, and 2 water molecules.

Step-by-step solution

Identifying the Reaction

This is an organic oxidation reaction where formaldehyde (HCHO) is being oxidized to formate ion (HCOO-). The oxidizing agent is a silver ammonia complex \(\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}\), and hydroxide ions (OH-) are also involved in the reaction.

Balancing Silver (Ag)

Since there are 2 atoms of silver (Ag) on the product side, we need 2 moles of the silver ammonia complex \(\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}\) on the reactant side.

Balancing Hydroxide Ions (OH-)

There are 3 hydroxide ions (OH-) on the reactant side and none on the product side explicitly, but we know they will form water (H2O). Therefore, we account for them by adding 2 water molecules to the product side.

Balancing Ammonia (NH3)

Each silver ammonia complex contains 2 moles of ammonia. Since there are 2 silver ammonia complexes, there are a total of 4 moles of ammonia released on the product side.

Balancing Water (H2O)

Starting with 3 hydroxide ions on the reactant side and knowing they will combine with protons to form 2 water molecules, we verify that water is already balanced with 2 molecules on the product side.

Verifying Other Atoms and Charge Balance

Each component of the reactant side is now accounted for on the product side. There is 1 carbon and 1 oxygen from HCHO on the reactant side forming 1 formate ion on the product side, 2 silver ions forming 2 solid silver atoms, and the ammonia count is balanced. The overall charge is also balanced, with the reactants and products each having a net charge of -1.

Key concepts

Organic Oxidation Reaction

Oxidation in organic chemistry refers to the process where a molecule, atom or ion loses electrons. However, it can also involve the gain of oxygen or the loss of hydrogen.

For an easy-to-understand example, consider the oxidation of formaldehyde (\text{HCHO}). In the given reaction, \text{HCHO} is oxidized to a formate ion (\text{HCOO}^-), which involves the gain of oxygen. Such reactions are essential in organic chemistry, playing a crucial role in energy generation and biosynthesis in living organisms.

Oxidation reactions require an oxidizing agent. Here, the silver ammonia complex, \text{Ag(NH\(_3\))\(_2\)}^+, acts as the oxidizing agent. It's not immediately apparent, but this complex efficiently accepts electrons from the formaldehyde, thereby oxidizing it. Organic oxidations can range from simple process like this to more complicated ones involved in breaking down organic molecules for energy.

Silver Ammonia Complex

Auditing the role of the silver ammonia complex, \text{Ag(NH\(_3\))\(_2\)}^+, is central to understanding this reaction. This complex is formed when silver ions react with ammonia. The silver ion is normally +1 charged, and when it coordinates with two molecules of ammonia, it forms a stable complex.

The complex is an effective oxidizing agent due to its ability to accept electrons readily. In this exercise, it accepts electrons from formaldehyde leading to the reduction of silver ion to metallic silver \text{Ag}, which is observed as a silver mirror in some classic chemistry experiments. The entire process serves as a fantastic illustration of redox chemistry, where the transfer of electrons is key to the reaction.

Understanding how coordination complexes like the silver ammonia complex work can shed light on various reactions, including those used in catalysis, photography, and even silver plating.

Balancing Chemical Equations

The principle of balancing chemical equations is rooted in the law of conservation of mass, indicating that matter is neither created nor destroyed in a chemical reaction. Consequently, every atom that enters a reaction must be accounted for among the products.

Starting with the original exercise, the balancing act commences by ensuring that there are equal numbers of each type of atom on both sides of the equation. Following the steps laid out in the solution, we begin by equalizing the amounts of silver and ammonia from the complex, followed by hydroxide ions that later form water. Furthermore, we ensure that the number of nitrogen and hydrogen atoms from ammonia (\text{NH\(_3\)}) also balance out.

Finally, we confirm the charge balance. In the given equation, this means ensuring that the combined charges of the reactants equals the combined charges of the products, which in this case is -1 for both. Balancing equations is a fundamental skill in chemistry that reinforces the understanding of chemical reactions and stoichiometry. It might seem like a simple task, but it's the cornerstone of understanding how different substances react in precise proportions.