Chemical Formula of Plaster of Paris is:

1. CaSO₄·2H₂O
2. CaSO₄·½H₂O
3. CaSO₄·H₂O
4. CaSO₄·3H₂O

Correct Answer: 2. CaSO₄·½H₂O

Plaster of Paris, with the formula CaSO₄·½H₂O, is a partially dehydrated form of gypsum that hardens when mixed with water. It’s widely used in construction, art, and medicine due to its quick-setting nature. While safe when handled properly, its production has some environmental impacts, and understanding its formula is key to appreciating its unique properties.

What is Plaster of Paris?

Plaster of Paris, or calcium sulfate hemihydrate (CaSO₄·½H₂O), is a powdery substance that hardens when mixed with water. It’s made by heating gypsum (CaSO₄·2H₂O) to remove some of its water content, leaving behind this half-hydrate form. The name comes from the large gypsum deposits near Paris, where it was first widely used. It’s super popular for making casts, sculptures, and even medical bandages.

When you add water to Plaster of Paris, it rehydrates and turns back into gypsum, forming a solid, durable structure. This quick-setting property is why it’s a favorite in creative and practical applications. Whether you’re crafting a statue or fixing a broken bone, this compound’s ability to mold and harden makes it a game-changer.

Quick Facts on Formula of Plaster of Paris

• Formula: CaSO₄·½H₂O (calcium sulfate hemihydrate).
• Common Name: Plaster of Paris.
• Production: Made by heating gypsum (CaSO₄·2H₂O) to 150–200°C.
• Uses: Construction, art, medical casts, dentistry.
• Safety: Avoid inhaling powder, handle wet mixture carefully.
• Environmental Note: Gypsum mining impacts ecosystems, but recycling is possible.

How Do You Make Plaster of Paris?

Making Plaster of Paris is all about transforming gypsum through controlled heating. Gypsum, which is CaSO₄·2H₂O, is heated to around 150–200°C to drive off three-quarters of its water molecules. This leaves you with CaSO₄·½H₂O, where the “½” indicates one water molecule shared between two calcium sulfate units. It’s a precise process that requires just the right temperature to avoid overcooking it into a different compound.

The resulting powder is fine and white, ready to be mixed with water for use. Industries produce it on a large scale, but the science behind it is simple enough to understand in a chemistry lab. The transformation from gypsum to Plaster of Paris is a great example of how heat can change a compound’s properties without altering its core elements.

Why CaSO₄·½H₂O and Not the Others?

The formula CaSO₄·½H₂O is unique because it reflects the specific water content that gives Plaster of Paris its properties. The other options—CaSO₄·2H₂O (gypsum), CaSO₄·H₂O, and CaSO₄·3H₂O—either have too much or too little water, which changes how they behave. For example, gypsum (CaSO₄·2H₂O) is already hydrated and doesn’t set like Plaster of Paris when mixed with water.

That “½H₂O” part is key because it shows the compound is partially dehydrated, making it eager to grab water and harden. This is why it’s used for molding and casting, unlike the other forms that don’t have the same reactivity. Knowing the exact formula helps you understand why Plaster of Paris works the way it does in both art and science.

Where Do We Use Plaster of Paris?

Plaster of Paris is everywhere once you start looking! In construction, it’s used to create smooth wall finishes, decorative moldings, and fire-resistant coatings. Artists love it for sculpting and casting detailed designs because it sets quickly and captures fine details. In medicine, it’s the go-to material for casts that keep broken bones in place while they heal.

It’s also used in dentistry for making dental molds and even in agriculture to improve soil structure. The fact that it’s cheap, easy to work with, and sets fast makes it a favorite across industries. Next time you see a beautifully carved ceiling or a perfectly set cast, you can thank Plaster of Paris for making it happen.

Handling Plaster of Paris Safely

While Plaster of Paris is generally safe, it’s not something you want to play around with carelessly. When mixing it with water, it can generate heat, so you need to be cautious to avoid burns, especially in large batches. Inhaling the dry powder can also irritate your lungs, so wearing a mask is a smart move when handling it in a classroom or workshop.

Always mix it in a well-ventilated area and follow the instructions for the right water-to-powder ratio to get the best results. Once it sets, it’s safe to handle, but during the mixing process, take care to avoid skin contact with the wet mixture, as it can cause irritation for some people.

Environmental and Industrial Considerations

Producing Plaster of Paris involves mining gypsum, which can have environmental impacts like habitat disruption. The heating process also uses energy, contributing to carbon emissions, though it’s less intensive than some other industrial processes. On the plus side, Plaster of Paris is recyclable in some cases, and gypsum waste can sometimes be reused in agriculture or construction.

Industries are exploring ways to make production more sustainable, like using renewable energy or recycling gypsum from construction waste. Its versatility and low cost keep it in high demand, but balancing its use with environmental responsibility is something chemists and engineers are working on for the future.

Summary

Question: Chemical Formula of Plaster of Paris is:
Answer: Chemical Formula of Plaster of Paris is CaSO₄·½H₂O.
Plaster of Paris is a fantastic example of how a simple chemical change can create a material with endless applications. Its formula, CaSO₄·½H₂O, is your ticket to understanding why it’s so useful in everything from art to medicine. For students, mastering this topic is a great way to connect chemistry to real-world uses.

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