Question

Aqueous sodium hydroxide is produced commercially by the electrolysis of aqueous sodium chloride. Hydrogen and chlorine gases are also produced. Write the balanced chemical equation for the production of sodium hydroxide. Include the physical states of the reactants and products.

Short answer

2 NaCl(aq) + 2 H₂O(l) → 2 NaOH(aq) + H₂(g) + Cl₂(g)

Step-by-step solution

- Identify the Reactants

The reactants for this process are aqueous sodium chloride (NaCl) and water (H₂O). These are involved in the electrolysis process.

- Identify the Products

The products of the reaction are aqueous sodium hydroxide (NaOH), hydrogen gas (H₂), and chlorine gas (Cl₂).

- Write the Unbalanced Equation

Write the unbalanced chemical equation for the electrolysis process: NaCl(aq) + H₂O(l) → NaOH(aq) + H₂(g) + Cl₂(g)

- Balance the Equation

Balance the chemical equation by ensuring that you have equal numbers of each type of atom on both sides of the equation. The balanced equation is: 2 NaCl(aq) + 2 H₂O(l) → 2 NaOH(aq) + H₂(g) + Cl₂(g)

- Confirm Physical States

Ensure that the physical states of all reactants and products are correctly labeled: Aqueous (aq) for sodium chloride and sodium hydroxide, liquid (l) for water, and gas (g) for hydrogen and chlorine.

Key concepts

Chemical Equations

A chemical equation represents a chemical reaction. It shows the reactants (starting materials) and the products (ending materials). The formula for each substance is included, and they are separated by an arrow. For instance, in the electrolysis of sodium chloride, the unbalanced equation is:
NaCl(aq) + H₂O(l) → NaOH(aq) + H₂(g) + Cl₂(g).
This equation indicates that sodium chloride and water react to form sodium hydroxide, hydrogen gas, and chlorine gas.

Balancing Equations

Balancing a chemical equation is critical. It ensures that the law of conservation of mass is followed. This means the number of each type of atom must be the same on both sides of the equation.
Start by writing the unbalanced equation:
NaCl(aq) + H₂O(l) → NaOH(aq) + H₂(g) + Cl₂(g).
Next, count the number of atoms for each element on both sides. Adjust the coefficients (numbers in front of formulas) to balance the atoms. The balanced equation for our example is:
2 NaCl(aq) + 2 H₂O(l) → 2 NaOH(aq) + H₂(g) + Cl₂(g).

Electrolysis Process

Electrolysis is a technique that uses electricity to cause a chemical reaction. In the case of sodium chloride, it splits the compound into sodium hydroxide, hydrogen gas, and chlorine gas. This process requires an electrolytic cell, which includes electrodes and an external power source.
Applied electricity breaks down the chemical bonds in reactants.
As a result, new substances are formed at the electrodes.

Aqueous Solutions

An aqueous solution is when a substance is dissolved in water. This is represented in chemical equations with the symbol (aq).
In our process, sodium chloride and sodium hydroxide exist as aqueous solutions.
This means they are dissolved in water, making the ions available for the electrolysis process.

Reactants and Products

Reactants are the starting substances in a chemical reaction. Products are the substances formed as a result of the reaction.
In the electrolysis of sodium chloride:

• Reactants are sodium chloride (NaCl) and water (H₂O).
• Products are sodium hydroxide (NaOH), hydrogen gas (H₂), and chlorine gas (Cl₂).

Identifying reactants and products helps us understand the chemical changes that occur during the reaction.