Problem 99 - A Complete Resource Book in Chemistry for JEE Main

Question

Carius method can be used to find \(\%\) of halogen sulphur in organic compounds. Here the compound is heated with fuming \(\mathrm{HNO}_{3}\) to get \(\mathrm{HX}\) or \(\mathrm{H}_{2} \mathrm{SO}_{4}\) followed by addition of \(\mathrm{AgNO}_{3}\) or \(\mathrm{BaCl}_{2}\) to get \(\mathrm{pt}\) of \(\mathrm{AgX}\) or \(\mathrm{BaSO}_{4}\) In Carius method sodium extract is boiled with \(\mathrm{HNO}_{3}\) it is for (a) To decompose \(\mathrm{NaCN}\) into \(\mathrm{HCN}(\mathrm{g})\) (b) To decompose \(\mathrm{Na}_{2} \mathrm{~S}\) into \(\mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})\) (c) To neutralise free alkali (d) all of these

Step-by-Step Solution

Answer

The correct answer is (d) all of these.

Step 1: Understanding the Carius Method

The Carius method is a laboratory technique used to quantify the content of halogens (like fluorine, chlorine, bromine, and iodine) and sulfur in organic compounds. During this process, the organic compound is heated with fuming nitric acid, which helps in the conversion of the compound into different acids or salts that can be precipitated out and weighed.

Step 2: Processing of Organic Compound Extracts

When a sodium extract from an organic compound is boiled with nitric acid (HNO_3), various reactions can take place, depending on the impurities in the sample. This can include the decomposition of sodium salts, such as NaCN or Na_2S, as well as the neutralization of free alkali present.

Step 3: Analyzing Potential Reactions

- NaCN with HNO_3 decomposes forming HCN(g). - Na_2S with HNO_3 decomposes forming H_2S(g). - Nitric acid also helps in neutralizing any free alkali (such as NaOH) that may be present.

Step 4: Conclusion on Reaction Functions

Based on the reactions identified, boiling the sodium extract with fuming HNO_3 addresses all of the mentioned chemical needs: decomposing NaCN, decomposing Na_2S, and neutralizing free alkali. Hence, the correct option is 'd) all of these'.

Key Concepts

Halogen Analysis

In the realm of organic chemistry, halogen analysis is a method used to determine the presence and quantity of halogens, such as fluorine, chlorine, bromine, and iodine, in organic compounds. These elements often appear in compounds as part of carbon-halogen bonds. During halogen analysis, the Carius method is frequently used.

This process involves heating the organic sample with fuming nitric acid ( HNO_3 ), causing the organic molecules to break down and form acids or salts that can be isolated. For instance, an organic compound containing a halogen can be converted into a hydrogen halide (HX) using nitric acid.

When silver nitrate ( AgNO_3 ) is added to the solution, the halide reacts to form a precipitate of silver halide ( AgX ), which can be weighed. The mass of this precipitate allows chemists to calculate the percentage of the specific halogen in the original compound.

Sulfur Quantification

Quantifying sulfur in organic compounds is critical for understanding their properties and chemical behavior. In the Carius method, sulfur quantification relies on converting sulfur in the compound to a sulfate salt.

During the process, sulfur is oxidized to produce sulfuric acid ( H_2SO_4 ) using fuming nitric acid ( HNO_3 ). This acid is subsequently treated with barium chloride ( BaCl_2 ) to form barium sulfate ( BaSO_4 ), a white precipitate. The precipitate is carefully isolated and weighed.

The weight of the barium sulfate allows for the determination of the sulfur content in the original organic compound. Since the reaction steps are well-defined, any measured precipitation can be directly translated into sulfur quantity through calculations based on stoichiometry.

Organic Chemistry Laboratory Techniques

Organic chemistry laboratory techniques encompass a wide range of procedures aimed at understanding and analyzing organic compounds. Among these, the Carius method stands out for its precision in analyzing halogen and sulfur content.

This technique exemplifies several essential lab skills:

• Careful heating and control of reaction conditions to ensure complete conversion of the compound.
• Handling of hazardous chemicals like fuming nitric acid with appropriate safety measures.
• Precipitation reactions where compounds are converted into insoluble forms for quantification.
• Meticulous weighing and recording of precipitates to determine the exact elemental content.

Mastering these techniques requires practice and attention to detail, making them critical for students in organic chemistry laboratories. They form the backbone of analytical techniques, ensuring accuracy and reliability in experimental results.