Question

$CaS{{O}_{4}}\cdot 2{{H}_{2}}O$ is also known as:
A. Gypsum
B. Anhydrite
C. Alabaster
D. Plaster of paris

Answer 1

Hint: Think about the common name for each of the given compounds, and what their water of hydration is. This will give you a clue as to what the given chemical formula is commonly known as.

Complete step by step answer:
We will look at the properties and the formulae for each of the given options one by one and then determine which is the correct option.
- Gypsum
Gypsum is a soft mineral that is composed of calcium sulphate dihydrate crystals. The chemical formula for gypsum is $CaS{{O}_{4}}\cdot 2{{H}_{2}}O$. It is mined as a mineral and is used as a fertilizer; it is also the main component of many types of plaster. Thus, this is a correct answer.

- Anhydrite
The name itself indicates that this chemical compound does not possess the water of hydration. The chemical formula for anhydrite or anhydrous calcium sulphate is $CaS{{O}_{4}}$. It is used as a drying agent and also in plasters along with gypsum. So, this is not the correct answer.

- Alabaster
This is known to be a variety of gypsum. It is lightly-tinted and ornamentally used as is referenced in many different forms of literature. The chemical formula for alabaster is $CaS{{O}_{4}}\cdot 2{{H}_{2}}O$. Thus, this is a correct answer.

- Plaster of paris
This plaster is made using gypsum as its main component and anhydrite as a drying agent. Plaster of paris is also known as calcium sulphate hemihydrate and has the chemical formula $CaS{{O}_{4}}\cdot {{H}_{2}}O$. It is used for many purposes but the major one of them is preparing casts, either for ornamental pieces or in medicine. Thus, this is not the correct answer.
So, the correct answer is “Option A and C”.

Note: Remember that if such a question is seen, and it is not mentioned that the question has multiple correct options then mark your answer as ‘A. Gypsum’ since it is the abundant and naturally found mineral rather than alabaster.