Question

Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.

Short answer

\( \text{Cl}_2 + \text{SO}_2 + 2\text{H}_2\text{O} \rightarrow 2\text{HCl} + \text{H}_2\text{SO}_4 \)

Step-by-step solution

Identify the Chemical Reaction

The problem states that chlorine is used and excess chlorine is treated with sulfur dioxide. The reaction in water involves chlorine (Cl₂) and sulfur dioxide (SO₂). The goal is to find the balanced chemical equation for this redox reaction.

Determine the Products

In the presence of water, chlorine and sulfur dioxide react to form hydrochloric acid (HCl) and sulfuric acid (H₂SO₄). Thus, the products of the reaction are HCl and H₂SO₄.

Write the Unbalanced Equation

With the reactants and products identified, the unbalanced chemical equation is: \[ \text{Cl}_2 + \text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{HCl} + \text{H}_2\text{SO}_4 \]

Balance the Equation

To balance the equation, ensure that there is the same number of each type of atom on both sides of the equation. The balanced chemical equation is: \[ \text{Cl}_2 + \text{SO}_2 + 2\text{H}_2\text{O} \rightarrow 2\text{HCl} + \text{H}_2\text{SO}_4 \]

Verify the Balanced Equation

Check each element to ensure balancing: there are 2 chlorine atoms, 1 sulfur atom, 4 hydrogen atoms, and 4 oxygen atoms on both sides of the equation. Therefore, the equation is correctly balanced.

Key concepts

Chlorine Purification in Water Treatment

Chlorine is commonly used in water treatment to purify drinking water. This process effectively disinfects water by killing bacteria and other pathogens. However, an excess of chlorine in drinking water can be harmful to humans, leading to health issues. To avoid this, it's essential to regulate the chlorine levels carefully.

Excess chlorine can be removed by a redox reaction with sulfur dioxide. This method ensures the leftover chlorine is neutralized safely, making the water fit for consumption. It's an important balance to maintain for effective water purification. In practice, enough sulfur dioxide is introduced to react with and remove the excess chlorine, highlighting the critical role of sulfur dioxide in this purification process.

Balancing Chemical Equations

Balancing chemical equations involves making sure that the number of atoms for each element is the same on both the reactant and product sides of the equation. This is necessary because the law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction.

When balancing the equation involving chlorine and sulfur dioxide, first identify each component:

• Reactants: chlorine (\( ext{Cl}_2 \)), sulfur dioxide (\( ext{SO}_2 \)), and water (\( ext{H}_2 ext{O} \))
• Products: hydrochloric acid (\( ext{HCl} \)) and sulfuric acid (\( ext{H}_2 ext{SO}_4 \))

The unbalanced chemical equation is: \[ ext{Cl}_2 + ext{SO}_2 + ext{H}_2 ext{O} ightarrow ext{HCl} + ext{H}_2 ext{SO}_4 \]

When balancing, start by balancing the atom count for elements like chlorine and sulfur, and then proceed to balance hydrogen and oxygen. Adjust coefficients to achieve equal atom counts on both sides. The final balanced equation is: \[ ext{Cl}_2 + ext{SO}_2 + 2 ext{H}_2 ext{O} ightarrow 2 ext{HCl} + ext{H}_2 ext{SO}_4 \] This illustrates a properly balanced equation, confirming that all elements respect the conservation of mass.

Reaction Between Sulfur Dioxide and Chlorine

The chemical reaction taking place when sulfur dioxide interacts with chlorine during water treatment is a redox reaction. A redox reaction involves the transfer of electrons between two species. In this particular reaction, chlorine undergoes reduction, gaining electrons, while sulfur dioxide is oxidized, losing electrons.

This redox process is crucial for reducing the excess chlorine in water. The molecular interaction helps in the conversion of chlorine into less harmful compounds, such as hydrochloric acid and sulfuric acid, ensuring that water purity is maintained without harmful chlorine levels.

• Chlorine, as a strong oxidizing agent, is effectively neutralized by sulfur dioxide.
• Sulfur dioxide is oxidized to form sulfuric acid.

Through this balanced chemical equation:\[ ext{Cl}_2 + ext{SO}_2 + 2 ext{H}_2 ext{O} ightarrow 2 ext{HCl} + ext{H}_2 ext{SO}_4 \], the neutralization process can be understood clearly. This equation underscores the transformation of excess chlorine into harmless byproducts, a crucial step in maintaining safe drinking water standards.