Which substance chars when heated with conc. \(H_2SO_4\)?

Carbohydrate

The correct answer is option 4. carbogydrate. 

Let us delve into the process of charring with concentrated sulfuric acid (H₂SO₄) and understand why carbohydrates are the ones that char.

Charring Process

Concentrated Sulfuric Acid (H₂SO₄) Properties:

Strong Acid: Concentrated sulfuric acid is a powerful dehydrating agent. It removes water from substances it comes into contact with.

Hydration and Decomposition: When sulfuric acid reacts with organic materials, it often causes dehydration and decomposition.

Reaction with Carbohydrates

Carbohydrates:

Carbohydrates like glucose, sucrose, and starches are organic compounds that contain carbon, hydrogen, and oxygen atoms in specific ratios. When carbohydrates are heated with concentrated sulfuric acid, the acid acts as a strong dehydrating agent, removing water (H₂O) molecules from the carbohydrate.

Formation of Carbon: The removal of water leads to the formation of elemental carbon. The sugar or carbohydrate turns into a black, carbonaceous residue, known as charring.

Example Reaction: Glucose with H₂SO₄:

\(\text{C}_6\text{H}_{12}\text{O}_6 \text{ (glucose)} + \text{H}_2\text{SO}_4 \rightarrow \text{C} + \text{other products}\) In this reaction, glucose is dehydrated to form carbon and other products, resulting in charring.

 Reaction with Other Substances

1. Proteins:

Proteins are complex molecules made up of amino acids. When heated with concentrated sulfuric acid, proteins are hydrolyzed into their amino acids. Proteins do not typically char; instead, they dissolve or form a dark solution due to hydrolysis.

2. Hydrocarbons:

Hydrocarbons (alkanes, alkenes) may react with sulfuric acid, especially under certain conditions, but they do not usually char. Instead, sulfuric acid may act as a catalyst or lead to other types of chemical reactions.

3. Fats: Fats are triglycerides composed of glycerol and fatty acids. Concentrated sulfuric acid hydrolyzes fats into glycerol and fatty acids. While fats decompose, they do not typically char like carbohydrates do.

Summary

When carbohydrates are heated with concentrated sulfuric acid, the acid dehydrates the carbohydrate, removing water and leaving behind a black residue of carbon. This process of charring is specific to carbohydrates due to their structure and the dehydrating properties of sulfuric acid. Other substances, like proteins, hydrocarbons, and fats, interact differently with sulfuric acid and do not undergo the same charring reactio