Problem 43 - Chemistry Matter and Change

Question

What is the reducing agent in this balanced equation? \(8 \mathrm{H}^{+}+\mathrm{Sn}+6 \mathrm{Cl}^{-}+4 \mathrm{NO}_{3}^{-1} \rightarrow\) \(\mathrm{SnCl}_{6}^{-2}+4 \mathrm{NO}_{2}+4 \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The reducing agent in this reaction is \(\mathrm{Sn}\), as its oxidation state increases from 0 to +4, indicating that it gets oxidized.

Step 1: Identify the oxidation state of each element

In this step, we will assign oxidation numbers to every element in each compound of the reaction. This will help us to track the changes in oxidation state. 8\(\ \mathrm{H}^{+}\) => Oxidation state of H: +1 \(\ \mathrm{Sn}\) => Oxidation state of Sn: 0 6\(\ \mathrm{Cl}^{-}\) => Oxidation state of Cl: -1 4\(\ \mathrm{NO}_{3}^{-}\) => Oxidation state of N: +5 and of O: -2 \(\mathrm{SnCl}_{6}^{-2}\) => Oxidation state of Sn: +4 and Cl: -1 4\(\ \mathrm{NO}_{2}\) => Oxidation state of N: +4 and O: -2 4\(\ \mathrm{H}_{2} \mathrm{O}\) => Oxidation state of H: +1 and O: -2

Step 2: Identify the change in oxidation states

Now we will look for the elements whose oxidation states change during the reaction. This will help us figure out which species is being reduced or oxidized. Sn: 0 => +4 (oxidation state increases, meaning it gets oxidized) N: +5 => +4 (oxidation state decreases, meaning it gets reduced)

Step 3: Identify the reducing agent

The reducing agent in a redox reaction is the species that gets oxidized, which means its oxidation state increases. In this reaction, the oxidation state of Sn increases from 0 to +4, indicating it gets oxidized. Therefore, the reducing agent is: \(\mathrm{Sn}\)

Key Concepts

Oxidation States

To grasp the concept of oxidation states, think of them as a bookkeeping method in chemistry that helps chemists keep track of electrons during reactions. An oxidation state, simply put, indicates the number of electrons an atom gains, loses, or shares when it forms bonds. To determine the oxidation state of an atom within a compound, certain rules are followed:

• In elemental form, the oxidation state is always zero. For example, in \(\mathrm{Sn}\), which is elemental tin, the oxidation state is 0.
• For ions composed of only one atom, the oxidation state is equal to the charge of the ion. Hence, \( \mathrm{H}^+ \) has an oxidation state of +1.
• In most compounds, oxygen has an oxidation state of -2, and hydrogen is +1, unless there are exceptions like in peroxides or hydrides.

Understanding oxidation states helps in identifying which elements gain or lose electrons, thereby giving insight into the redox reactions they undergo.

Redox Reaction

Redox reactions are a class of chemical reactions that involve the transfer of electrons between two species. The term "redox" is derived from two words: "reduction" and "oxidation". These reactions are fundamental to many processes in chemistry and biology.In a redox reaction:

• Reduction refers to the gain of electrons by a molecule, atom, or ion.
• Oxidation is the loss of electrons from a molecule, atom, or ion.

These reactions can be easily identified through changes in oxidation states of the substances involved. If an element's oxidation number decreases, it is reduced; if it increases, the element is oxidized. In the exercise, tin (\( \mathrm{Sn} \)) is oxidized as its oxidation number increases, and nitrogen in nitrate (\( \mathrm{NO}_3^- \)) is reduced as its number decreases.

Electron Transfer

Electron transfer is at the heart of redox reactions. It involves the movement of electrons from one element to another, which changes the oxidation state and is essentially what makes a redox reaction occur. During a redox reaction:

• Electrons are transferred from the species being oxidized to the species being reduced.
• The substance that donates electrons and becomes oxidized is called the reducing agent.
• The substance that accepts electrons and becomes reduced is called the oxidizing agent.

In our given reaction, tin (\ \( \mathrm{Sn} \ \)) loses electrons as it is oxidized from an oxidation state of 0 to +4. These electrons are gained by nitrate ions, reducing them.

Oxidation and Reduction

Oxidation and reduction are like two sides of the same coin. They describe two types of chemical processes that are always paired together in redox reactions. Let's dissect these processes:

• Oxidation means an increase in oxidation state due to a loss of electrons. Oxygen adds to a compound or hydrogen is removed. Example: Sn in \( \mathrm{Sn} \ \) to \( \mathrm{SnCl}_6^{-2} \). Sn goes from 0 to +4 by losing electrons.
• Reduction is a decrease in oxidation state due to a gain of electrons. It often involves the gain of hydrogen or loss of oxygen from a substance. Example: Nitrogen in \( \mathrm{NO}_3^- \) is reduced to \( \mathrm{NO}_2 \) as its oxidation state decreases from +5 to +4.

These complementary processes are fundamental to numerous chemical reactions, including combustion, metal extraction, and cellular respiration.