Answer the questions based on the passage given below:

Adsorption is a surface phenomenon and it differs from absorption which occurs throughout the body of the substance that absorbs. In physisorption the attractive forces are mainly van der Waals forces while in chemisorption ionic / covalent bonds are formed between particles of adsorbent and adsorbate. The catalytic activity of finely divided iron in Haber's process of ammonia manufacture can be explained by adsorption theory. Adsorption being an exothermic process, the heat of adsorption is utilized in enhancing the rate of the reaction. Adsorption has many applications being used in gas masks, control of humidity, chromatograph separation, curing diseases etc.

Chromatography is based on:

Physical adsorption

The correct answer is option 1. Physical adsorption.

Chromatography is a separation technique used to analyze and separate the components of a mixture based on their interactions with two phases: a stationary phase and a mobile phase.

Stationary Phase: This is the phase that remains fixed in place within the chromatographic system. It can be a solid or a liquid supported on a solid.

Mobile Phase: This is the phase that moves through or over the stationary phase, carrying the sample components with it. It can be a liquid or a gas.

Separation Mechanisms in Chromatography:

1. Physical Adsorption:

Physical adsorption (or physisorption) refers to the attachment of molecules to a surface through weak, non-covalent interactions like van der Waals forces and hydrogen bonding.

Adsorption Chromatography: In this type of chromatography, the stationary phase is a solid or a liquid-coated solid. Sample components are separated based on their different affinities (adsorption strengths) to the stationary phase.

Example: In normal-phase chromatography, the stationary phase is typically a polar solid (like silica gel), and the mobile phase is a non-polar solvent. Polar components of the sample adsorb more strongly to the stationary phase and move more slowly, while non-polar components travel faster with the mobile phase.

Significance: Physical adsorption is crucial because it determines how components of a mixture interact with the stationary phase and therefore how they are separated. The differential adsorption leads to different retention times for the components.

2. Chemical Adsorption:

Chemical adsorption (or chemisorption) involves the formation of strong, covalent bonds between the adsorbate and the surface.

Affinity Chromatography: In some chromatography methods, such as affinity chromatography, chemical adsorption is employed. Here, specific interactions between the sample components and the stationary phase occur, often involving biochemical or functional groups.

Example: In affinity chromatography, the stationary phase is coated with ligands that specifically bind to certain biomolecules (like antibodies binding to antigens). This selective binding is based on chemical interactions, but the separation still involves differential retention.

Significance: While chemical adsorption can enhance specificity, most chromatography techniques primarily rely on physical adsorption for separation.

3. Homogeneous Catalysis:

Homogeneous catalysis involves a catalyst that is in the same phase (usually liquid) as the reactants. The catalyst speeds up a reaction without being consumed and is distributed uniformly throughout the solution.

Role in Chromatography: Chromatography is not a catalytic process. It’s a separation technique, so homogeneous catalysis is not relevant to chromatography. Chromatography does not involve the use of catalysts to alter the reaction rate but rather focuses on the separation of mixtures.

4. Heterogeneous Catalysis:

Heterogeneous catalysis involves a catalyst that is in a different phase (usually solid) from the reactants, which are typically in a liquid or gas phase. The reaction occurs at the surface of the solid catalyst.

Role in Chromatography: Similar to homogeneous catalysis, heterogeneous catalysis is not relevant to chromatography. Chromatography does not involve catalytic reactions but instead involves separating components based on their interactions with the stationary and mobile phases.

Chromatography is primarily based on physical adsorption, where the interaction between the sample components and the stationary phase is governed by weak physical forces. This is the fundamental mechanism in most chromatographic techniques, such as normal-phase and reversed-phase chromatography. Chemical adsorption can play a role in specialized chromatography methods, like affinity chromatography, where specific chemical interactions are utilized. However, it is not the primary mechanism for most chromatography techniques. Catalysis (both homogeneous and heterogeneous) is not involved in the fundamental separation process of chromatography.

Thus, the separation in chromatography largely hinges on physical adsorption, where components of the mixture adhere differently to the stationary phase, leading to their separation as they move with the mobile phase.