Question

Brine solution on electrolysis will not give: (a) \(\mathrm{O}_{2}\) (b) \(\mathrm{H}_{2}\) (c) \(\mathrm{Cl}_{2}\) (d) \(\mathrm{NaOH}\)

Short answer

The answer is (a) \(\mathrm{O}_{2}\) will not be given during brine electrolysis.

Step-by-step solution

Understanding the Electrolysis of Brine

Brine is a concentrated solution of sodium chloride (\(\text{NaCl}\)) in water. During electrolysis, the brine solution is electrolyzed to form different products.

Identifying Possible Products

In the electrolysis of brine, the major products formed are chlorine gas (\(\mathrm{Cl}_{2}\)) at the anode, hydrogen gas (\(\mathrm{H}_{2}\)) at the cathode, and sodium hydroxide (\(\mathrm{NaOH}\)) in solution. Oxygen gas (\(\mathrm{O}_{2}\)) is not typically produced in this process.

Analyzing Each Option

To determine what will not be given during electrolysis: - Chlorine (\(\mathrm{Cl}_{2}\)) is produced at the anode, so option (c) is incorrect.- Hydrogen (\(\mathrm{H}_{2}\)) is produced at the cathode, so option (b) is incorrect.- Sodium hydroxide (\(\mathrm{NaOH}\)) forms in solution, so option (d) is incorrect.- Oxygen (\(\mathrm{O}_{2}\)) is not typically produced during the standard electrolysis of brine, so option (a) is correct.

Key concepts

Anode Reactions

In electrolysis, the anode is the positively charged electrode where oxidation occurs. During the electrolysis of brine, chloride ions (\( ext{Cl}^-\) from the dissolved \( ext{NaCl}\) are attracted to the anode. They lose electrons and form chlorine gas. This is an oxidation reaction because the chloride ions are losing electrons:

• At the anode: \(2\text{Cl}^- ightarrow \text{Cl}_2 + 2\text{e}^-\)

Chlorine gas (\(\text{Cl}_2\)) bubbles are formed at the anode, which is why it's crucial that the anode material does not react with chlorine. Suitable anode materials should be resistant to halogen attack to avoid corrosion.

Cathode Reactions

At the cathode, which is negatively charged, reduction reactions take place. In brine electrolysis, water molecules are reduced to form hydrogen gas. Sodium ions (\(\text{Na}^+\)) are also present in the solution but have a higher reduction potential compared to water. As a result, water is reduced instead of sodium ions. The reaction at the cathode is:

• At the cathode: \(2\text{H}_2\text{O} + 2\text{e}^- \rightarrow \text{H}_2 + 2\text{OH}^-\)

Hydrogen gas (\(\text{H}_2\)) emerges at the cathode. The formation of hydroxide ions (\(\text{OH}^-\)) in this process is crucial for producing sodium hydroxide in the solution. This reduction reaction exemplifies how electrons are gained, allowing the conversion of water to gaseous hydrogen.

Chlorine Production

Chlorine production is a fundamental outcome of brine electrolysis. As the chloride ions are oxidized at the anode, they are converted into chlorine gas. Chlorine, a vital industrial chemical, is commonly collected and used in many applications. These include:

• Disinfecting and cleaning water supplies, making them safe to drink.
• Production of plastics, such as polyvinyl chloride (PVC).
• Fabrication of bleaches and various solvents.

The process of generating chlorine is energy-intensive. It requires careful monitoring to ensure maximum efficiency and safety due to the toxic and reactive nature of chlorine.

Sodium Hydroxide Formation

Sodium hydroxide, also known as lye, is another significant product formed during the electrolysis of brine. When chloride ions are oxidized to form chlorine, and water is reduced to generate hydrogen, the resulting \(\text{OH}^-\) ions pair with \(\text{Na}^+\) ions present in the solution. This combination forms sodium hydroxide. The chemical reaction can be summarized as follows:

• \(\text{Na}^+ + \text{OH}^- \rightarrow \text{NaOH}\)

Sodium hydroxide is widely used in various industries, such as paper manufacturing, soap making, and chemical synthesis. Its strong alkalinity makes it valuable as a reagent for neutralization and other chemical processes. Massive industrial applications of sodium hydroxide derive directly from its production in the chlor-alkali process, which involves brine electrolysis.