Difference Between Calcium Sulfate and Plaster of Paris

The key difference between calcium sulfate and plaster of Paris is that calcium sulfate is an inorganic compound having a calcium cation and sulfate anion, whereas plaster of Paris is a material containing calcium sulfate hemihydrates.

The term calcium sulfate is common in chemistry laboratories, while the term plaster of Paris is common in medical laboratories and artistry. It is because the plaster of Paris is a material that can be used for moulding.

CONTENTS

1. Overview and Key Difference
2. What is Calcium Sulfate 
3. What is Plaster of Paris
4. Side by Side Comparison – Calcium Sulfate vs Plaster of Paris in Tabular Form
6. Summary

What is Calcium Sulfate?

Calcium sulfate is an inorganic compound having the chemical formula CaSO₄. It occurs commonly in its hydrated forms. Also, the molar mass of the anhydrous calcium sulfate is 136.14 g/mol. It appears as a white solid in room temperature. Furthermore, this white solid is odourless.

The major source of calcium sulfate is gypsum, a naturally occurring mineral. Another important source is anhydrite. These two deposits occur as evaporates. Also, we can obtain the mineral via two pathways: via open-cast quarrying or via deep mining. In addition to that, we can obtain calcium sulfate as a byproduct of many different processes, such as flue-gas desulfurization, production of phosphoric acid from phosphate rock, production of hydrogen fluoride, etc. Furthermore, when calcium sulfate is produced, we can observe it in three different stages: anhydrous form, dihydrated form, and hemihydrate form.

Moreover, there are different uses of calcium sulfate. It is useful in the production of plaster of Paris, production of stucco, in the food industry as coagulants, etc. It is also used as a firming agent, a leavening agent, and as a desiccant in different applications.

What is Plaster of Paris?

We can produce plaster of Paris from gypsum. People have used this material from ancient times. People living in areas near Paris used this material widely, to make plaster and cement. They also used it to do ornamental work on ceilings and cornices. So, this is how the name plaster of Paris came into being. Plaster of Paris contains the calcium sulfate hemihydrates (CaSO₄·0.5H₂O).

Moreover, we can prepare this compound by heating the gypsum, which contains calcium sulfate dihydrate (CaSO₄·2H₂O), to a temperature of about 150°C (120-180°C). Above this, we should add certain additives when heating.

Besides, Plaster of Paris is a fine, white powder. When it becomes hydrated, we can use it to mould things, and if we allow it to dry, it hardens and retains whatever the shape is set before drying.

What is the Difference Between Calcium Sulfate and Plaster of Paris?

Calcium sulfate is an inorganic compound having the chemical formula CaSO₄, but plaster of Paris contains calcium sulfate. The key difference between calcium sulfate and plaster of Paris is that calcium sulfate is an inorganic compound having a calcium cation and sulfate anion, whereas plaster of Paris is a material containing calcium sulfate hemihydrates.

Below infographic provides a detailed description of the difference between calcium sulfate and plaster of Paris.

Summary – Calcium Sulfate vs Plaster of Paris

Plaster of Paris contains calcium sulfate. The key difference between calcium sulfate and plaster of Paris is that calcium sulfate is an inorganic compound having a calcium cation and sulfate anion, whereas plaster of Paris is a material containing calcium sulfate hemihydrates.

Reference:

1. Alden, Andrew. “Get to Know the 7 Delicate Sulfate Minerals.” ThoughtCo, Feb. 11, 2020, Available here.
2. “Calcium Sulfate.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.

Image Courtesy:

1. “CaSO4” By Smokefoot – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Calcium sulfate hemihydrate” (Public Domain) via Commons Wikimedia