Which of the following is an example of hydrolysis?
A. because of a reaction with acid rain, sandstone, develops black surface deposits
B. Because of a reaction with oxygen, iron changes into rust
C. Because of a reaction with water, feldspar is changed into clay minerals
D. Because of a reaction with carbon acid, limestone is dissolved
The Correct Answer and Explanation is:
The correct answer is C. Because of a reaction with water, feldspar is changed into clay minerals.
Explanation of Hydrolysis
Hydrolysis is a chemical process where water molecules interact with a substance, leading to the breakdown of that substance. In the context of minerals and geological processes, hydrolysis is a key weathering mechanism.
Feldspar, which is a common silicate mineral found in many igneous rocks, undergoes hydrolysis when it reacts with water. This reaction involves the breaking of the chemical bonds within feldspar. Feldspar is typically composed of aluminosilicate, containing silicon (Si), aluminum (Al), potassium (K), sodium (Na), and calcium (Ca). When feldspar comes into contact with water, it reacts chemically, leading to the transformation of feldspar into clay minerals, primarily kaolinite.
The general reaction can be summarized as follows:
[
\text{Feldspar} + \text{Water} \rightarrow \text{Clay minerals} + \text{Soluble ions}
]
In this process, water molecules contribute hydroxyl ions (OH⁻) and hydrogen ions (H⁺), which interact with the feldspar’s crystalline structure. The aluminum and silicon within the feldspar become soluble, leading to the formation of clay minerals, which are more stable in the weathering environment. This transformation is significant in soil formation, as clay minerals contribute to the physical and chemical properties of soils.
The other options presented do not involve hydrolysis:
- A describes a reaction of sandstone with acid rain, which is more of a chemical weathering reaction but not specifically hydrolysis.
- B is the oxidation of iron, resulting in rust, which is a different process known as oxidation rather than hydrolysis.
- D refers to the dissolution of limestone in carbonic acid, a process of carbonation rather than hydrolysis.
In summary, hydrolysis is specifically exemplified by the transformation of feldspar into clay minerals through its reaction with water, highlighting the crucial role of water in geological weathering processes.