Problem 10 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

An organic compound ' \(A\) ' is oxidized with \(\mathrm{Na}_{2} \mathrm{O}_{2}\) followed by boiling with \(\mathrm{HNO}_{3}\). The resultant solution is then treated with ammonium molybdate to yield a yellow precipitate. Based on above observation, the element present in the given compound is: (a) Nitrogen (b) Phosphorus (c) Fluorine (d) Sulphur

Step-by-Step Solution

Answer

The element present in the compound is phosphorus.

Step 1: Understand the Reaction

Given that compound 'A' is oxidized with \(\mathrm{Na}_{2}\mathrm{O}_{2}\), this is an indicator that a weak base or oxygen donor is used to oxidize the compound. After this, boiling with \(\mathrm{HNO}_{3}\) is applied, which is a strong oxidizing agent, likely breaking down organic components to more stable ions or acids.

Step 2: Identify Result of Oxidation

The process with \(\mathrm{HNO}_{3}\) likely yields an oxidized version of any present element. In many classic reactions, \(\mathrm{HNO}_{3}\) oxidizes phosphorus to phosphoric acid, fluorine to fluorides, and sulfur to sulfates.

Step 3: Examine the Role of Ammonium Molybdate

Ammonium molybdate is used as a reagent to test for phosphates, where it reacts with phosphates under acidic conditions to form a yellow precipitate known as ammonium phosphomolybdate.

Step 4: Conclusion from Observations

The formation of a yellow precipitate when the resultant solution is treated with ammonium molybdate is indicative of the presence of phosphates. Since ammonium molybdate is specifically used to test for phosphorus, element 'A' contains phosphorus.

Key Concepts

Oxidation reactions

Oxidation reactions involve the transfer of electrons between molecules, which typically results in the increase of oxygen content in a substance or the loss of hydrogen. Understanding this process is essential in organic chemistry as it helps in determining the composition and properties of organic compounds.

In the context of the original exercise, the oxidation of compound 'A' is facilitated using sodium peroxide (\(\mathrm{Na}_{2} \mathrm{O}_{2}\)). This reagent acts as a weak base or oxygen donor. Following this, nitric acid (\( \mathrm{HNO}_{3} \)) is used, which is a strong oxidizing agent. This compound is capable of breaking down organic materials due to its ability to donate oxygen and introduce changes in the structural composition of molecules.

This two-step oxidation results in the transformation of potential elements within the organic compound to their oxidized forms. Each element reacts to form specific products: nitrogen can form nitrates, phosphorus transforms into phosphoric acid, and sulfur changes into sulfates. Recognizing these reactions allows chemists to deduce the element by examining what the oxidation products are.

Ammonium molybdate test

The Ammonium molybdate test is a highly specific chemical test used to detect phosphorus or phosphate ions in a solution. It is commonly used in chemical analysis due to its sensitivity and specificity.

During the test, ammonium molybdate reacts with phosphate ions under acidic conditions, such as those resulting from nitric acid. This reaction leads to the formation of a yellow precipitate known as ammonium phosphomolybdate. The appearance of this yellow precipitate is a clear indicator of the presence of phosphorus in the sample being analyzed.

In many organic compound analyses, this test is crucial because it provides unambiguous evidence of phosphorus, distinguishing it from other elements that may not produce a visible reaction with ammonium molybdate. It's a definitive method often used in laboratories to confirm phosphorus presence and is a critical step in various chemical examination processes.

Organic compounds analysis

Analyzing organic compounds involves understanding the composition and structure of a substance to determine its chemical properties. This typically includes identifying the functional groups present and the elements that make up the compound.

The steps in compound analysis often involve:

• Oxidation reactions: To break down the compound into its constituent elements or simpler molecules for easier identification.
• Specific chemical tests: Like the ammonium molybdate test, to confirm the presence of elements such as phosphorus.
• Observations and results analysis: Interpreting the changes that occur during the reactions to draw conclusions about the compound's composition.

In the exercise, the analysis process starts with oxidizing the unknown organic compound 'A'. This serves to potentially convert all elemental parts into their oxidized forms, allowing for easier detection using chemical tests.

Such thorough analysis helps in identifying the presence of specific elements like phosphorus, which is detected through the yellow precipitate formed with ammonium molybdate. This approach is standard in organic compound analysis for constructing a comprehensive understanding of the material's chemical behavior.