Question

Chlorine gas was first prepared by Carl Wilhelm Scheele in 1774 by the reaction of sodium chloride, manganese(IV) oxide, and sulfuric acid. In addition to chlorine, the reaction produces water, sodium sulfate, and manganese(II) sulfate. Write the balanced equation for this reaction.

Short answer

The balanced equation is: \(2\text{NaCl} + \text{MnO}_2 + 2\text{H}_2\text{SO}_4 \rightarrow \text{Cl}_2 + 2\text{H}_2\text{O} + \text{Na}_2\text{SO}_4 + \text{MnSO}_4\).

Step-by-step solution

Write the Chemical Formula for Each Compound

First, list the chemical formulas for each compound and element involved in the reaction: \(\text{Sodium chloride} = \text{NaCl}\) \(\text{Manganese(IV) oxide} = \text{MnO}_2\) \(\text{Sulfuric acid} = \text{H}_2\text{SO}_4\) \(\text{Chlorine gas} = \text{Cl}_2\) \(\text{Water} = \text{H}_2\text{O}\) \(\text{Sodium sulfate} = \text{Na}_2\text{SO}_4\) \(\text{Manganese(II) sulfate} = \text{MnSO}_4\).This step sets the foundation to balance the chemical equation.

Write the Unbalanced Chemical Equation

Use the chemical formulas to write down the unbalanced equation: \[\text{NaCl} + \text{MnO}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{Cl}_2 + \text{H}_2\text{O} + \text{Na}_2\text{SO}_4 + \text{MnSO}_4\] This equation includes all reactants and products in the reaction but does not yet have the correct coefficients for balance.

Balance the Chlorine Atoms

Determine the number of chlorine atoms on both sides. You have one \(\text{NaCl}\) contributing one chlorine atom and \(\text{Cl}_2\) as a product. Set two \(\text{NaCl}\) molecules on the reactant side to balance with \(\text{Cl}_2\): \[ 2\text{NaCl} + \text{MnO}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{Cl}_2 + \text{H}_2\text{O} + \text{Na}_2\text{SO}_4 + \text{MnSO}_4 \]

Balance Sodium and Sulfate Ions

Balance sodium and sulfate by ensuring equal numbers across reactants and products. You need two sodium ions from \(\text{NaCl}\) for \(\text{Na}_2\text{SO}_4\), which is already present from the balance achieved in Step 3.

Balance Hydrogen and Oxygen Atoms

For sulfuric acid and water, match hydrogens and oxygens by balancing sulfuric acid and water molecules. Use one \(\text{H}_2\text{SO}_4\) to match one \(\text{H}_2\text{O}\) and complete the balancing: \[2\text{NaCl} + \text{MnO}_2 + 2\text{H}_2\text{SO}_4 \rightarrow \text{Cl}_2 + 2\text{H}_2\text{O} + \text{Na}_2\text{SO}_4 + \text{MnSO}_4\] This corrects hydrogen and oxygen unbalances.

Final Review and Conclude

Review each side of the equation to ensure all elements are balanced. Reassess the atom counts for each element to validate that no imbalances remain. The balanced chemical equation is:\[2\text{NaCl} + \text{MnO}_2 + 2\text{H}_2\text{SO}_4 \rightarrow \text{Cl}_2 + 2\text{H}_2\text{O} + \text{Na}_2\text{SO}_4 + \text{MnSO}_4\] Successfully balancing the equation confirms accuracy.

Key concepts

Chlorine Gas Preparation

Chlorine gas, known for its pale green color and distinctive sharp smell, was first isolated in 1774 by the Swedish chemist Carl Wilhelm Scheele. This was achieved through a chemical reaction involving sodium chloride, manganese(IV) oxide, and sulfuric acid. The process is crucial because it laid the foundation for chlorine production used in various applications such as water purification and industrial processes.
In Scheele's reaction, chlorine gas is one of the products formed. The reaction can be represented as follows:

• Sodium chloride (NaCl) and sulfuric acid (H₂SO₄) react to form sodium sulfate (Na₂SO₄), releasing hydrogen chloride gas (HCl) in the process.
• Hydrogen chloride gas then reacts with manganese(IV) oxide (MnO₂) to produce chlorine gas (Cl₂), water (H₂O), and manganese(II) sulfate (MnSO₄).

The correct balancing of these chemical equations ensures that all atoms are accounted for properly on either side of the reaction, maintaining the principle of conservation of mass.

Sodium Chloride

Sodium chloride, commonly known as table salt, is an essential compound not just in daily life but also in chemical reactions. It consists of sodium (Na) and chlorine (Cl) atoms. In the preparation of chlorine gas, sodium chloride serves as a crucial reactant.
When sodium chloride reacts with sulfuric acid, it initially forms sodium sulfate and hydrogen chloride. This transformation is significant in driving the reaction forward as the hydrogen chloride contributes to chlorine gas formation when further reacted with manganese(IV) oxide.
It's important to recognize the role of sodium ions here. They pair with sulfate ions from sulfuric acid to create sodium sulfate, a stable salt that contributes to the balance of the overall chemical equation.

Manganese(IV) Oxide

Manganese(IV) oxide, with the chemical formula MnO₂, plays a pivotal role as an oxidizing agent in the preparation of chlorine gas. This compound effectively increases the oxidation state of specific elements involved in the reaction.
In Scheele's discovery, manganese(IV) oxide facilitates the conversion of hydrogen chloride into chlorine gas. It does so by accepting electrons during the reaction, thereby being reduced to manganese(II) sulfate (MnSO₄).
This change in oxidation states is a key aspect of redox reactions where one species is reduced while another is oxidized. Understanding the function of MnO₂ is vital for mastering the prediction and balance of similar chemical reactions.

Sulfuric Acid

Sulfuric acid, one of the most potent acids, is known for its strong dehydrating properties and is widely used in industry. In the reaction for chlorine gas preparation, sulfuric acid acts as a reactant and plays multiple roles.
As a primary component, it facilitates the separation of sodium ions, leading to the formation of sodium sulfate. This interaction underscores its property of being a strong electrolyte and its ability to donate protons.
Additionally, sulfuric acid contributes to the generation of hydrogen chloride gas. When heated, hydrogen chloride is capable of reacting with manganese(IV) oxide to yield chlorine gas.
Grasping these functions of sulfuric acid is crucial for understanding many industrial and laboratory processes that involve acids in chemical synthesis and reactions.