Certified Fire Investigator Practice Exam

What is the process called that occurs in gypsum when it is exposed to heat?

1. Dehydration

2. Calcination

3. Crystallization

4. Combustion

The correct answer is: Calcination

The process that occurs in gypsum when it is exposed to heat is known as calcination. During calcination, gypsum (which is calcium sulfate dihydrate, CaSO4·2H2O) loses water molecules and transforms into calcium sulfate hemihydrate (CaSO4·0.5H2O), commonly known as plaster of Paris. This transformation not only involves the removal of water but also changes the physical and chemical properties of the material, making it useful for a range of applications, particularly in construction and art. Dehydration refers specifically to the loss of water from a substance but does not explicitly indicate the thermal transformation related to gypsum. While it describes an aspect of what occurs during calcination, it lacks the specificity of relating directly to the thermal reaction that gypsum undergoes. Crystallization is a different process involving the solidification of a substance from a solution or melt, creating crystal structures, which doesn’t accurately describe the profound physical change that gypsum experiences under heat. Combustion describes a high-energy chemical reaction, typically involving oxygen, that results in fire, which is not relevant to the thermal treatment of gypsum. Thus, understanding the specific chemical transformation that occurs upon heating gypsum is essential to grasping why calcination