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.

Short answer

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

Step-by-step solution

Identify the Reactants and Products

First, let's identify the reactants and the products in the reaction. The reactants are aluminum metal \((Al)\) and perchloric acid \((HClO_4)\). The products of the reaction are hydrogen gas \((H_2)\) and aluminum perchlorate \((Al(ClO_4)_3)\).

Write the Balanced Molecular Equation

The balanced molecular equation can be written by placing the correct coefficients that balance each element on both sides. \[2Al(s) + 6HClO_4(aq) \rightarrow 3H_2(g) + 2Al(ClO_4)_3(aq)\] This equation shows two aluminum atoms reacting with six perchloric acid molecules to produce three hydrogen gas molecules and two aluminum perchlorate molecules.

Dissociate Strong Electrolytes

In aqueous solutions, strong acids and salts dissociate into ions. Perchloric acid \((HClO_4)\) and aluminum perchlorate \((Al(ClO_4)_3)\) can dissociate as follows: - \(HClO_4(aq)\) dissociates to \(H^+(aq)\) and \(ClO_4^-(aq)\). - \(Al(ClO_4)_3(aq)\) dissociates to \(Al^{3+}(aq)\) and \(ClO_4^-(aq)\) ions.

Write the Full Ionic Equation

Replace the dissociated species in the balanced molecular equation to form the full ionic equation. Strong electrolytes are expressed as their ions:\[2Al(s) + 6H^+(aq) + 6ClO_4^-(aq) \rightarrow 3H_2(g) + 2Al^{3+}(aq) + 6ClO_4^-(aq)\]

Cancel Spectator Ions to Write the Net Ionic Equation

The ions that appear on both sides of the equation and do not participate in the reaction are called spectator ions. In this case, \(ClO_4^-(aq)\) is the spectator ion. By canceling it out, we obtain the net ionic equation:\[2Al(s) + 6H^+(aq) \rightarrow 3H_2(g) + 2Al^{3+}(aq)\]

Key concepts

Balanced Molecular Equation

A balanced molecular equation is essential for understanding the stoichiometry of a chemical reaction. In our exercise, we deal with the reaction between aluminum metal and perchloric acid. The main task is to ensure that the number of atoms for each element is the same on both sides of the equation. This equation not only tells us what the reactants and products are but also the proportions in which they react.### Steps to Balance:- **Identify Reactants and Products:** The reaction involves aluminum \( Al \) and perchloric acid \( HClO_4 \) as the reactants. The products are hydrogen gas \( H_2 \) and aluminum perchlorate \( Al(ClO_4)_3 \).- **Balance Atoms:** We balance by counting atoms. Aluminum and hydrogen should be balanced by adjusting their coefficients as needed.- **Final Balanced Molecular Equation:** \[2Al(s) + 6HClO_4(aq) \rightarrow 3H_2(g) + 2Al(ClO_4)_3(aq)\] This equation tells us that 2 moles of aluminum react with 6 moles of perchloric acid to produce 3 moles of hydrogen gas and 2 moles of aluminum perchlorate.This step-by-step approach helps in visualizing how each molecule participates in the reaction and ensures the law of conservation of mass is upheld.

Net Ionic Equation

In chemical reactions occurring in aqueous solutions, ions often provide a clearer picture of the actual species that undergo change. The net ionic equation focuses specifically on the species that are involved in the chemical change, ignoring the spectator ions.### Writing the Net Ionic Equation:1. **Dissociation of Strong Electrolytes:** When dissociating components like perchloric acid \( HClO_4 \), it gives \( H^+ \) and \( ClO_4^- \) ions. Aluminum perchlorate \( Al(ClO_4)_3 \) dissociates into \( Al^{3+} \) and \( ClO_4^- \) ions.2. **Develop the Full Ionic Equation:** With these ions, the balanced molecular equation becomes: \[2Al(s) + 6H^+(aq) + 6ClO_4^-(aq) \rightarrow 3H_2(g) + 2Al^{3+}(aq) + 6ClO_4^-(aq)\]3. **Cancel Out Spectator Ions:** The \( ClO_4^- \) ions do not change during the reaction and are thus not part of the net ionic equation.### Resulting Net Ionic Equation:- The resulting simplified equation is: \[2Al(s) + 6H^+(aq) \rightarrow 3H_2(g) + 2Al^{3+}(aq)\]This equation highlights the reaction's core changes, omitting distractions from species that do not participate directly in the reaction.

Spectator Ions

Spectator ions are ions present in the reaction mixture that do not participate in the actual chemical transformation. Instead, they remain unchanged and appear on both sides of the ionic equation.### Identifying Spectator Ions:- **Role Understanding:** These ions are simply "bystanders," watching the reaction proceed without getting involved.- **Spotting Them in Equations:** In our reaction, perchlorate ions \( ClO_4^- \) are the spectator ions. They appear in the reactant side as part of perchloric acid \( HClO_4 \) and remain in the product side in aluminum perchlorate \( Al(ClO_4)_3 \).- **Equation Reduction:** By identifying and removing these ions from the full ionic equation, we focus on the species undergoing chemical change.Spectator ions help maintain charge balance within the solution, but they do not affect the stoichiometry of the net ionic equation. Understanding their role is crucial for writing accurate net ionic equations.