Plaster of paris:
**Core Concept**
Plaster of Paris is a type of calcium sulfate hemihydrate (CaSO4·½H2O) used as a casting material in orthopedic and medical settings. It is derived from the natural mineral gypsum (CaSO4·2H2O) and undergoes a hydration reaction when mixed with water.
**Why the Correct Answer is Right**
When Plaster of Paris comes into contact with water, it undergoes a rapid exothermic reaction to form calcium sulfate dihydrate (CaSO4·2H2O), also known as gypsum. This process releases heat and forms a rigid, yet porous, solid that can be molded and shaped. The hydration reaction is characterized by the absorption of 1.5 molecules of water per molecule of Plaster of Paris, resulting in the formation of a stable, insoluble crystal lattice.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the chemical composition of Plaster of Paris.
**Option B:** This option is incorrect as it does not mention the hydration reaction that occurs when Plaster of Paris is mixed with water.
**Option C:** This option is incorrect as it does not provide a clear description of the properties or uses of Plaster of Paris.
**Clinical Pearl / High-Yield Fact**
It's essential to note that Plaster of Paris is not suitable for use in wet environments, as it can absorb moisture and lose its rigidity. Additionally, it is not recommended for use on broken skin or in areas with poor circulation, as it can cause tissue necrosis.
**Correct Answer:** D.