Question

Which of the following is an example of absorption? (a) Oxygen on metal surface (b) Hydrogen on finely divided nickel (c) Water on calcium chloride (d) Water on silica gel

Short answer

(c) Water on calcium chloride

Step-by-step solution

Understanding the Question

The question asks to identify a process of absorption among the given options. Absorption involves a substance being taken into the interior of a material, unlike adsorption, where it accumulates on the surface.

Analyzing Option A

Option (a) states "Oxygen on metal surface," which is a classic example of adsorption, where oxygen molecules adhere to the surface of metal. Thus, it is not absorption.

Analyzing Option B

Option (b) states "Hydrogen on finely divided nickel," which is another example of adsorption, as the hydrogen gas adheres to the surface of nickel particles. Therefore, it is not absorption.

Analyzing Option C

Option (c) states "Water on calcium chloride," where calcium chloride absorbs water and transforms, such as forming a hydrated compound. This is indicative of absorption, where water is taken into the structure of calcium chloride.

Analyzing Option D

Option (d) states "Water on silica gel," which is an example of adsorption since water molecules adhere to the surface of silica gel, rather than being absorbed into it.

Conclusion and Answer Selection

Considering the explanations and analysis above, option (c) "Water on calcium chloride" is the correct answer as it represents absorption.

Key concepts

Absorption Process

Absorption is a process where a substance is taken into the interior of another material. It is like a sponge soaking up water. This means the absorbate permeates into the entire volume of the material. Unlike adsorption, which only occurs on the surface, absorption ensures that the absorbed particle becomes fully integrated within the absorbing material. This process is commonly encountered in various applications like conditioning air, where moisture is absorbed by salts or other hygroscopic substances.
To put it simply, an example of absorption is when water is absorbed by a paper towel. The water doesn't just sit on the surface; it permeates into the towel's fibers. This is crucial in distinguishing between absorption and adsorption because absorption involves the diffusion of molecules throughout the material rather than just accumulating on the surface.

Adsorption Examples

Adsorption is when molecules bind to the surface of a solid or liquid. Unlike absorption, adsorption does not involve any internal diffusion. Instead, it is often characterized by the adhesion of molecules, atoms, or ions from a gas, liquid, or dissolved solid onto a surface. Common examples of adsorption include:

• Activated carbon filters purifying water by adsorbing impurities onto carbon surfaces.
• Silica gel packets in shoe boxes which adsorb moisture to prevent mold.
• Adsorption of gas molecules on surfaces like metal or nickel catalysts.

These examples help illustrate how adsorption is critical in numerous industrial and environmental applications. This process plays a significant role in catalytic reactions, separation processes, and even in daily-use products to maintain freshness and prevent moisture damage.

Chemical Interactions with Water

Water's interactions with other substances highlight both absorption and adsorption processes. Since water is a polar molecule, it has a unique ability to interact with different materials. These interactions depend on the chemical properties of the materials involved.
When water comes into contact with calcium chloride, for example, absorption occurs. This is due to calcium chloride's hygroscopic nature, meaning it naturally absorbs moisture from the air. The water participates in a chemical reaction, forming a hydrated compound, thereby being completely integrated within the calcium chloride structure.
In contrast, when water encounters silica gel, adsorption occurs. Silica gel has a large surface area which traps water molecules on the surface, rather than absorbing them. Hence, water's versatility plays an essential role in the efficiency of these two distinct processes and their applications in various industries.

Calcium Chloride Properties

Calcium chloride is a chemical compound with a variety of useful properties. It is highly soluble in water and is known for its ability to absorb moisture, making it an excellent drying agent in many situations. This is especially useful in environments where moisture control is essential. For example, it's often used in de-icing roads because of its ability to lower the freezing point of water.
At a molecular level, calcium chloride consists of one calcium ion and two chloride ions. This ionic nature contributes to its hygroscopic properties, allowing it to readily attract and absorb water. When it absorbs water, it forms various hydrates, which can be used in different industrial applications ranging from refrigeration to concrete mixing.
In summary, the defining characteristics of calcium chloride underscore its effectiveness as an absorbent material, particularly in processes that heavily rely on moisture regulation.