Plaster of Paris should be stored in moisture proof containers. Explain why?

Plaster of Paris (PoP) is a hydrous calcium sulfate. When it comes into contact with moisture, it undergoes a chemical reaction known as hydration. This reaction transforms the dry powder form of PoP into a hard solid.

Here are the steps explaining why PoP should be stored in moisture-proof containers:

1. Chemical Composition: Plaster of Paris is chemically known as Calcium Sulphate hemihydrate. It is obtained by heating gypsum or calcium sulphate dihydrate to about 140-180 degree Celsius. When gypsum is heated to such a temperature, it loses three-quarters of its water content leading to the formation of Plaster of Paris.

2. Hydration Reaction: The Plaster of Paris that we get is a dry powder. When this powder is mixed with water, it rehydrates, meaning it gains back the water molecules it had lost. This process is called hydration. During hydration, the mixture of PoP and water sets into a hard solid mass due to the heat generated in the exothermic reaction.

3. Premature Setting: If Plaster of Paris is not stored in a moisture-proof container, it can absorb moisture from the air. This can lead to a premature hydration reaction, causing the Plaster of Paris to harden without it being used.

4. Loss of Properties: Once the Plaster of Paris has set, it cannot be converted back into the powder form. This means that any PoP that has hardened due to exposure to moisture cannot be used and is wasted.

5. Prevention of Wastage: To prevent wastage and to maintain the usability of the Plaster of Paris, it is important to store it in moisture-proof containers. This prevents any moisture from the air from reaching the PoP and triggering the hydration reaction.

In conclusion, Plaster of Paris should be stored in moisture-proof containers to prevent it from hardening due to a premature hydration reaction, which would render it unusable.

Plaster of Paris (PoP) is a hydrous calcium sulfate. When it comes into contact with moisture, it undergoes a chemical reaction known as hydration. This reaction transforms the PoP into a hard solid.

Here are the steps explaining why PoP should be stored in moisture-proof containers:

1. Chemical Composition: Plaster of Paris is chemically known as Calcium Sulphate hemihydrate. It is obtained by heating gypsum or calcium sulphate dihydrate to about 140°C - 180°C. When water is added to the Plaster of Paris, it re-forms into gypsum.

2. Hydration Process: The process of hardening is actually hydration where water molecules are added to the plaster. When Plaster of Paris is mixed with water it is chemically changed into gypsum again, and this new gypsum forms a matrix that traps the water molecules. This is what causes the plaster to harden and set.

3. Moisture Absorption: If Plaster of Paris is left exposed to the air, it can absorb moisture from the surrounding environment. This can trigger the hydration process, causing the plaster to harden even without adding water.

4. Preventing Premature Hardening: To prevent the Plaster of Paris from hardening prematurely, it should be stored in a moisture-proof container. This will prevent any moisture from the air from being absorbed by the plaster and triggering the hydration process.

5. Maintaining Usability: Keeping Plaster of Paris in a moisture-proof container also helps to maintain its usability. If it hardens prematurely, it can't be used for its intended purposes, such as making casts or molds.

In conclusion, Plaster of Paris should be stored in moisture-proof containers to prevent it from absorbing moisture from the environment, which would trigger the hydration process and cause the plaster to harden prematurely. This ensures that the Plaster of Paris remains usable for as long as possible.