Problem 96 - General Chemistry

Question

Aluminum metal reacts with perchloric acid to produce hydrogen gas and a solution of aluminum perchlorate. Write the molecular equation for this reaction. Then write the corresponding net ionic equation.

Step-by-Step Solution

Answer

The net ionic equation is: \[ 2Al(s) + 6H^+(aq) \rightarrow 3H_2(g) + 2Al^{3+}(aq) \]

Step 1: Identify Reactants and Products

The reactants in this chemical reaction are aluminum metal (Al) and perchloric acid (HClO₄). The products are hydrogen gas (H₂) and aluminum perchlorate (Al(ClO₄)₃) in aqueous solution.

Step 2: Write the Balanced Molecular Equation

The balanced chemical reaction for the reaction between aluminum metal and perchloric acid is written as:\[ 2Al(s) + 6HClO₄(aq) \rightarrow 3H_2(g) + 2Al(ClO₄)_3(aq) \]

Step 3: Identify the States and Strong Electrolytes

Aluminum metal is a solid (s), perchloric acid is aqueous (aq), hydrogen gas is gaseous (g), and aluminum perchlorate is aqueous (aq). Perchloric acid is a strong acid, and aluminum perchlorate is a soluble ionic compound, which fully dissociates in water.

Step 4: Write the Complete Ionic Equation

Represent the strong electrolytes (aqueous substances) as ions in the reaction:\[ 2Al(s) + 6H^+(aq) + 6ClO_4^-(aq) \rightarrow 3H_2(g) + 2Al^{3+}(aq) + 6ClO_4^-(aq) \]

Step 5: Cancel Spectator Ions to Find Net Ionic Equation

Identify and cancel the spectator ions, which do not change during the reaction. In this reaction, \(ClO_4^-\) appears on both sides:\[ 2Al(s) + 6H^+(aq) \rightarrow 3H_2(g) + 2Al^{3+}(aq) \]

Step 6: Write the Net Ionic Equation

The net ionic equation, simplified, for the reaction is:\[ 2Al(s) + 6H^+(aq) \rightarrow 3H_2(g) + 2Al^{3+}(aq) \]

Key Concepts

Chemical Reaction

A chemical reaction occurs when substances interact, resulting in the formation of new products. In this scenario, aluminum metal reacts with perchloric acid. This is a simple exchange of atoms or ions where new bonds are formed, leading to the creation of hydrogen gas and aluminum perchlorate.
In most chemical reactions:

• The reactants are the substances present at the beginning.
• The products are the substances formed after the reaction.

Understanding the nature of the reactants and products helps predict the reaction outcome.

Molecular Equation

The molecular equation provides a detailed view of a chemical reaction by showing all the reactants and products in their original form. For the reaction between aluminum metal and perchloric acid, the molecular equation is:
\[ 2Al(s) + 6HClO_4(aq) \rightarrow 3H_2(g) + 2Al(ClO_4)_3(aq) \]
This equation shows:

• 2 aluminum atoms reacting.
• 6 perchloric acid molecules participating.
• The formation of hydrogen gas and aluminum perchlorate.

A molecular equation offers a clear view of the stoichiometry of the reaction.

Balanced Equation

Balancing an equation is essential in ensuring the conservation of mass, as atoms cannot be created or destroyed. Each type of atom present in the reactants must also be accounted for in the products.
In the balanced equation \( 2Al(s) + 6HClO_4(aq) \rightarrow 3H_2(g) + 2Al(ClO_4)_3(aq) \), the quantities reflect that:

• 2 moles of aluminum react with 6 moles of perchloric acid.
• The reaction produces 3 moles of hydrogen gas.
• 2 moles of aluminum perchlorate are formed.

Balancing is crucial as it provides the correct proportions, ensuring no atoms are lost or gained.

Aluminum Metal

Aluminum metal, denoted as \(Al\), is a lightweight, silvery-white metal known for its high conductivity and resistance to corrosion. In the given reaction:

• Aluminum acts as a reducing agent, donating electrons.
• It forms aluminum ions \((Al^{3+})\) upon reacting with the acid.

Aluminum's ability to lose electrons and form positive ions is a key aspect of its reactivity, especially in acidic conditions.

Perchloric Acid

Perchloric acid, \(HClO_4\), is a strong mineral acid known for its high reactivity. It fully dissociates in water, meaning it splits into hydrogen ions \((H^+)\) and perchlorate ions \((ClO_4^-)\). In this reaction:

• The hydrogen ions react with aluminum metal, facilitating the release of hydrogen gas.
• The perchlorate ions remain unchanged as spectator ions.

Understanding the properties of perchloric acid, including its ability to fully dissociate, is crucial for predicting its behavior in reactions.