How to Balance the Chemical Equation for Aluminum and Hydrochloric Acid

Aluminum reacts with hydrochloric acid to produce aluminum chloride and hydrogen gas. This reaction is a classic example of an acid-base reaction and also a redox reaction. Here, we will demonstrate how to balance the chemical equation for this process step by step.

Skeletal Equation

The skeletal equation for the reaction between aluminum (Al) and hydrochloric acid (HCl) is:

Skeletal equation: Al HCl -> AlCl3 H2

Balancing the Equation

Let's start by balancing the left-hand side (LHS) and the right-hand side (RHS) of the equation.

Left-Hand Side (LHS)

On the LHS, we have:

Aluminum (Al): 1 Hydrogen (H): 1 Chlorine (Cl): 1

Right-Hand Side (RHS)

On the RHS, we have:

Aluminum (Al): 1 Chlorine (Cl): 3 Hydrogen (H): 2

Clearly, the equation is not balanced. We need to add coefficients to balance it.

Balanced Equation

To balance the equation, we need to multiply the number of HCl molecules by 6:

Balanced equation: 2Al 6HCl -> 2AlCl3 3H2

Let's verify:

Left-Hand Side (LHS)

Aluminum (Al): 2 Hydrogen (H): 6 Chlorine (Cl): 6

Right-Hand Side (RHS)

Aluminum (Al): 2 Chlorine (Cl): 6 Hydrogen (H): 6

Now the equation is balanced.

Redox Formalism

The reaction can also be analyzed using redox formalism. Let's break it down step-by-step:

Reduction Half-Reaction

Hydrogen ions (H ) are reduced to form hydrogen gas (H2):

H e- -> 1/2 H2

This half-reaction can be multiplied by 3 to balance the number of electrons:

3H 3e- -> 3/2 H2

Oxidation Half-Reaction

Aluminum (Al) is oxidized to aluminum ions (Al3 ):

Al -> Al3 3e-

Adding the two half-reactions together, we get:

Al 3H 3e- -> Al3 3e- 3/2 H2

The electrons cancel out:

Al 3H -> Al3 3/2 H2

To form aluminum chloride (AlCl3), we add chloride ions (Cl-).

Al 3HCl -> AlCl3 3/2 H2

Multiplying both sides by 2 to balance the equation:

2Al 6HCl -> 2AlCl3 3H2

This confirms the balanced chemical equation.