Problem 31 - A Complete Resource Book in Chemistry for JEE Main

Question

Schiff's solution B is obtained when (a) sulphurous acid is passed through magenta dye (b) chlorine is passed through magenta dye (c) both (a) and (b) (d) none of the above

Step-by-Step Solution

Answer

(a) sulphurous acid is passed through magenta dye.

Step 1: Understanding Schiff's Solution B

Schiff's solution is a reagent used in the detection of aldehydes. Schiff's bases form when aldehydes react with an amine in the dye. It is typically formed by treating magenta dye with sulphurous acid.

Step 2: Analyzing the Options Given

We are given the options for producing Schiff's solution B: (a) passing sulphurous acid through magenta dye, (b) passing chlorine through magenta dye, (c) both (a) and (b), and (d) none of the above. We need to determine which process is the correct way to form Schiff's solution B.

Step 3: Matching the Process to the Correct Option

Known chemistry tells us that Schiff's reagent, or Schiff's solution, is known to specifically involve passing sulphurous acid through magenta dye to become decolorized in the presence of aldehydes. Chlorine does not have the same effect in forming Schiff's solution. Therefore, option (a) is the correct answer.

Key Concepts

Sulphurous Acid

Sulphurous acid is a key component in the formation of Schiff's reagent. It is actually derived from the dissolution of sulfur dioxide in water, where it forms a weak acid. Despite its name, it's not often found in its free form. Instead, it is usually encountered in solution.

When used in chemical reactions, sulphurous acid behaves as a reducing agent. This means it can donate electrons to another substance. When we pass sulphurous acid through magenta dye, an important transformation occurs. This transformation forms the basis for Schiff's reagent, crucial for aldehyde detection.

• Sulphurous acid acts to remove the intense color of the magenta dye.
• It converts the dye to a colorless form, which is essential for its role as a reagent.

This process is highly specific and is fundamental in the application of Schiff's reagent in chemistry labs.

Magenta Dye

Magenta dye, also known as fuchsine, is a synthetic dye and has an important role in the creation of Schiff's reagent. In its original state, this dye has a bright magenta color. This trait is useful in visualizing the chemical changes that occur when it interacts with sulphurous acid.

The interaction between magenta dye and sulphurous acid is a remarkable chemical reaction:

• The magenta dye turns colorless when treated with sulphurous acid.
• This reaction does not just alter the color; it prepares the dye to react specifically with aldehydes.

Once decolorized, the dye can effectively signify the presence of aldehydes by undergoing another change in color when aldehydes are present. This makes magenta dye not just a visual indicator but a critical component in detecting aldehydes within samples.

Aldehyde Detection

Aldehyde detection is an essential process in many chemical analyses, and Schiff's reagent is a key tool in this process. When a sample containing aldehydes is introduced to the colorless Schiff's reagent, a distinctive color change occurs.

Here's how the detection works:

• The presence of aldehydes causes the colorless Schiff's reagent to turn pink or magenta.
• This color change is a direct indicator that aldehydes are present in the sample.

This method is particularly useful because it provides both a qualitative and somewhat quantitative assessment of aldehydes, based on the intensity of the color change.
This technique is widely used in laboratories around the world due to its simplicity and effectiveness. By using Schiff's reagent, scientists can quickly determine the presence of aldehydes without the need for more complex instrumentation.