HESI General Chairside Assisting Practice Exam

How can gypsum be described in its unrefined state?

1. As a monohydrate

2. As a trihydrate

3. As a dihydrate

4. As a hemihydrate

The correct answer is: As a dihydrate

Gypsum, in its unrefined state, is primarily composed of calcium sulfate dihydrate. This means that each molecule consists of two water molecules for every molecule of calcium sulfate. The term "dihydrate" refers to the chemical structure and hydration level of gypsum, which is significant in understanding its properties and uses in various applications, especially in dentistry and construction. In contrast, the other terms refer to different forms or states of calcium sulfate which occur when gypsum undergoes changes in its water content. A monohydrate would imply only one water molecule is present, whereas a hemihydrate indicates partial dehydration, containing only half a water molecule for each formula unit of calcium sulfate. A trihydrate would suggest an entirely different composition with three water molecules, which does not occur in the context of gypsum. Recognizing gypsum as a dihydrate is essential for applying its characteristics accurately within dental and material science contexts.