What is the chemical name and formula for Plaster of Paris?
Did you know Plaster of Paris has been known since ancient times, and its name comes from the abundant gypsum deposits found near Paris, France? That's the Paris connection. But what is Plaster of Paris called in chemistry? Let's find out in this article.
Did you know Plaster of Paris has been known since ancient times, and its name comes from the abundant gypsum deposits found near Paris, France? That's the Paris connection.
Gypsum plaster was used in ancient Egypt for building pyramids. Plaster of Paris is commonly referred to as PoP. Yes, the smooth wall finishes, decorative mouldings, and surgical casts you see are Plaster of Paris.
What is Plaster of Paris? It is a quick-setting gypsum plaster consisting of a fine white powder (the name we will learn further in this article). The white powder hardens when moistened and allowed to dry.
Plaster of Paris is a favourite of sculptors, as the speed at which the plaster sets helps them to cast their idea quickly.
Now back to the chemistry angle. Plaster of Paris (POP) is a chemical compound, and so it has a chemical name and formula also.
In this article, we will learn the IUPAC name for Plaster of Paris, just as we did for salt, vinegar, diamond, CNG, and many more.
What is the chemical name and formula for Plaster of Paris?
The chemical name for Plaster of Paris, or gypsum plaster, is calcium sulphate hemihydrate.
The chemical formula is CaSO₄.1/2 H₂O, indicating that a half molecule of water of crystallisation is bound to each calcium sulphate unit.
It is to be noted that though PoP is made out of gypsum, which is calcium sulphate dihydrate rather than hemihydrate.
So, in simple words, Plaster of Paris is formed by dehydration or heating of gypsum (calcium sulphate dihydrate) to about 120 to 180 degrees Celsius to form calcium sulphate hemihydrate.
Properties of Plaster of Paris
Appearance: Fine, white powder
Setting: Sets quickly and becomes a hard solid within minutes when mixed with water
Texture: Becomes hard, yet porous
Mouldability: Can be easily moulded
Adhesion: Sticks well to surfaces like wood, metal, and ceramics
Rehydration: Can absorb water to revert to gypsum
Composition: Calcium sulphate hemihydrate
Exothermic: Setting process releases a small amount of heat
Source: Wikipedia and Britannica
Uses of Plaster of Paris
Plaster of Paris (PoP) is used in medicine, construction, art & crafts, laboratories, dentistry, and firefighting. Below, let's have a quick look at the uses of Plaster of Paris:
Construction and Decoration
- Wall & Ceiling Finishes
- Moulding (pottery, ceramics, statues, architectural elements)
- Fireproofing (applied to wood and metal to prevent fire spread)
Medical and Dental
- Orthopaedic Casts (fractured bones)
- Dentistry (filling gaps, models of teeth, dental impressions)
- Radiotherapy
Art, Crafts and Industrial
- Sculpting
- Chalk
- Cosmetics
Laboratory and Other Uses
- Sealing air gaps in lab apparatus
- Funeral homes (tissue reconstruction or limb repair)
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Roopashree Sharma is an experienced broadcast journalist with over 7 years of experience, specialising in beats including geopolitics, defence, and general awareness. She has worked in the roles of correspondent and producer for leading media houses, including Zee, WION, and Economic Times. Currently serving as Deputy Manager – Editorial at Jagran New Media, she produces explainer articles and videos for the General Knowledge (GK) section of the Jagran Josh (English) portal. For inquiries, contact her at roopashree.sharma@jagrannewmedia.com.
