A Level Chemistry OCR Practice Exam

What does adsorption entail in chemical processes?

1. A liquid forming a new phase

2. A solute being dissolved in a solvent

3. A substance being held to the surface of another

4. A gas escaping into the atmosphere

The correct answer is: A substance being held to the surface of another

Adsorption is a process where molecules adhere to the surface of a solid or liquid, forming a layer of the adsorbate (the substance being adsorbed) on the adsorbent (the surface). This is a surface phenomenon, distinct from absorption, where a substance permeates or is incorporated into another phase. In adsorption, the interaction is primarily physical or sometimes chemical, involving forces such as van der Waals forces or chemical bonding, depending on the nature of the substances involved. The other options do not relate to the concept of adsorption. For instance, the formation of a new phase represents a different type of reaction, where substances undergo a transformation, completely different from mere adherence of particles to a surface. Similarly, a solute dissolving in a solvent describes a homogenous mixture or solution formation rather than surface interactions. Lastly, the escape of gas into the atmosphere involves phase transition, not surface interaction, and thus does not convey the meaning of adsorption.