Problem 6 - Chemistry in 30 days

Question

Which one of the following acts as an antichlor ? (a) \(\mathrm{MnO}_{2}\) (b) \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (d) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\)

Step-by-Step Solution

Answer

(b) \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) acts as an antichlor.

Step 1: Understanding the concept of an antichlor

Antichlor is a chemical compound used to remove the excess chlorine in a bleaching process. It chemically neutralizes or decomposes chlorine.

Step 2: Identifying the common antichlor

The most commonly used antichlor is sodium thiosulfate (n11 1S2O3), as it effectively neutralizes chlorine without causing damage to fabrics or other materials.

Step 3: Analyzing the options

Given the options: (a) M1O2, (b) a11 1S2O3, (c) 1K1C11O21, and (d) a11SO4, option (b) sodium thiosulfate matches the compound known to specifically act as an antichlor.

Step 4: Verifying the function of sodium thiosulfate

Sodium thiosulfate (n11 1S2O3) reacts with chlorine to neutralize it: \( 11 0S2O3^{2-} + Cl0_{2} 1 1\rightarrow 1Cl^{-} + 1SO4^{2-} \). This confirms it acts effectively as an antichlor.

Key Concepts

Sodium Thiosulfate

Sodium thiosulfate is a versatile chemical compound widely used in various applications. It is particularly known for its role as an antichlor. As an antichlor, sodium thiosulfate neutralizes residual chlorine left behind after bleaching processes.
Sodium thiosulfate has the chemical formula \(\mathrm{Na}_2\mathrm{S}_2\mathrm{O}_3\). It works effectively by transforming chlorine, which could otherwise be destructive or harmful, into less harmful substances.

• This reaction ensures that fabrics and other materials maintain their integrity and avoid potential damage from leftover chlorine.
• This property makes it a common choice for industries requiring safe and effective chlorine neutralization.

Chlorine Neutralization

Chlorine neutralization is a crucial step in processes where chlorine's reactive nature could lead to undesirable outcomes. In the context of bleaching and other chemical processes, any unreacted chlorine must be neutralized to protect materials from damage.
The primary purpose of chlorine neutralization is to convert chlorine gas or aqueous chlorine into chloride ions and less reactive substances. Sodium thiosulfate plays a significant role in this procedure by reacting with the chlorine to neutralize its harmful effects.

• The reaction transforms chlorine into chloride ions \(\mathrm{Cl}^−\) and thiosulfate into sulfate ions \(\mathrm{SO}_4^{2-}\).
• This reaction is effective because it removes the active chlorine species, thus preventing further oxidation reactions which could cause damage to materials.

Chemical Reactions in Bleaching

In the bleaching process, chemical reactions play a vital role as they are used to remove color from materials. Bleaching agents, such as chlorine, are used for their powerful oxidizing capabilities. However, the leftover chlorine after the initial bleaching process must be neutralized, often using antichlors.
This is essential because excess chlorine can continue to react undesirably with materials, potentially causing degradation or weakening their structure. Sodium thiosulfate, used as an antichlor, helps avert these undesirable reactions.

• In the reaction, sodium thiosulfate interacts with chlorine to produce neutral and less harmful substances.
• This is essential for maintaining the quality and longevity of bleached materials, as unchecked chlorine could cause oxidative damage over time.