Question

The reaction between ammonium perchlorate and aluminum is discussed in the "Chemistry in Focus" segment Oxidation-Reduction Reactions Launch the Space Shuttle. The reaction is labeled as an oxidation-reduction reaction. Explain why this is an oxidationreduction reaction and defend your answer.

Short answer

The reaction between ammonium perchlorate (NH4ClO4) and aluminum (Al) is an oxidation-reduction (redox) reaction because there is a transfer of electrons between the reactants and products. Aluminum undergoes oxidation, as its oxidation state changes from 0 to +3, while chloride undergoes reduction, as its oxidation state changes from +7 to -1. The balanced chemical equation for this reaction is: 6 NH4ClO4 + 10 Al → 10 Al2O3 + 6 NH4Cl + 3 N2 + 9 H2O

Step-by-step solution

Understand oxidation-reduction reactions

An oxidation-reduction reaction (or redox reaction) is a type of chemical reaction that involves the transfer of electrons between two species. In a redox reaction, one species loses electrons (undergoes oxidation) while another species gains electrons (undergoes reduction). The species that loses electrons is called the reducing agent, and the species that gains electrons is called the oxidizing agent.

Write down the chemical formula for both reactants

Before analyzing the reaction between ammonium perchlorate and aluminum, we need to write down their chemical formulas. Ammonium perchlorate is NH4ClO4, and aluminum is represented by the symbol Al.

Identify the oxidation states of the elements in the reactants

To determine if the reaction between ammonium perchlorate and aluminum is a redox reaction, we need to identify the initial oxidation states of all the elements involved. In NH4ClO4, the oxidation state of N is -3, H is +1, Cl is +7, and O is -2. In aluminum, the oxidation state of Al is 0 (as it is an uncombined elemental form).

Write the balanced chemical equation for the reaction

The balanced chemical equation for the reaction between ammonium perchlorate (NH4ClO4) and aluminum (Al) is: 6 NH4ClO4 + 10 Al → 10 Al2O3 + 6 NH4Cl + 3 N2 + 9 H2O

Identify the oxidation states of the elements in the products

Now, we need to identify the oxidation states of the elements in the products of the reaction. In Al2O3, the oxidation state of Al is +3, and O is -2. In NH4Cl, the oxidation state of N is -3, H is +1, and Cl is -1. In N2, the oxidation state of N is 0. In H2O, the oxidation state of H is +1, and O is -2.

Determine if the reaction is a redox reaction

In order to confirm if the reaction between ammonium perchlorate and aluminum is a redox reaction, we will check if there is a transfer of electrons (change in oxidation states) between the reactants and products. From the analysis in steps 3 and 5, we can observe: - The oxidation state of Al changes from 0 (reactant) to +3 (product). This indicates that aluminum has lost electrons and undergoes oxidation. - The oxidation state of Cl changes from +7 (reactant) to -1 (product). This indicates that chloride has gained electrons and undergoes reduction. Since there is a transfer of electrons between the reactants and products, the reaction between ammonium perchlorate and aluminum is indeed an oxidation-reduction reaction.

Key concepts

Oxidation States

Oxidation states, also known as oxidation numbers, are a way to keep track of electron distribution in atoms or ions during a chemical reaction. They are represented by integers that can be positive, negative, or zero depending on the element's situation.
Assigning oxidation states helps identify how electrons are transferred in a chemical reaction.

• Elements in their elemental form have an oxidation state of 0.
• For monoatomic ions, the oxidation state is equal to the charge of the ion.
• Common rules apply, such as hydrogen usually having an oxidation state of +1 and oxygen having -2, except in peroxides.

In the reaction between ammonium perchlorate and aluminum, each element's oxidation state is used to identify which elements undergo oxidation and reduction. Before the reaction, for example, aluminum has an oxidation state of 0 as it is in its elemental form, while chlorine in NH4ClO4 has an oxidation state of +7. After the reaction, changes in these values indicate a transfer of electrons between the reactants.

Electron Transfer

Electron transfer is the movement of electrons from one species to another and is the central process in redox reactions. In these reactions, oxidation involves losing electrons, while reduction involves gaining electrons. This is often remembered with the acronym "OIL RIG":

• Oxidation Is Loss.
• Reduction Is Gain.

Electrons do not float freely but are transferred between specific atoms or ions within reactants and products. In the reaction discussed, aluminum atoms lose electrons, while chlorine atoms gain them.

• The oxidation state change from 0 to +3 in aluminum indicates it loses three electrons per atom, thus being oxidized.
• In chloride, the oxidation state decreases from +7 to -1, indicating a gain of electrons, marking it as the reduced species.

Understanding electron transfer is crucial for correctly balancing redox reactions and predicting the outcomes of chemical processes.

Chemical Equations

Chemical equations represent the reactants and products in a chemical reaction and must be balanced to reflect the law of conservation of mass. This means the number of atoms of each element must be the same on both sides of the equation.
In redox reactions like the one between ammonium perchlorate and aluminum, it's also important to balance charges, making sure the total charge is equal on both sides.
This involves sometimes adding coefficients in front of reactants and products to ensure both mass and charge balance is achieved.

• For example, in the chemical equation: \[ 6 \text{NH}_4\text{ClO}_4 + 10 \text{Al} \rightarrow 10 \text{Al}_2\text{O}_3 + 6 \text{NH}_4\text{Cl} + 3 \text{N}_2 + 9 \text{H}_2\text{O} \],

Balanced with respect to both atoms and charge, it shows that electrons lost by aluminum are gained by chlorine.

This balancing is key to confirming that redox reactions have occurred as expected, showing electron transfer from the reactants to the products, and ensuring the reliability of the results.