What is the formula of gypsum?

Question

Accepted Answer

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate. This comprehensive reference provides all essential formulas related to gypsum and its various forms, designed for students studying chemistry, geology, and materials science.

Gypsum Formulas

Formula Type	Chemical Formula	Common Name	Molecular Weight	Water Content	Description
Primary Gypsum Formula	CaSO₄·2H₂O	Gypsum (Dihydrate)	172.17 g/mol	2 water molecules	Natural hydrated calcium sulfate mineral
Anhydrous Gypsum Formula	CaSO₄	Anhydrite	136.14 g/mol	0 water molecules	Completely dehydrated form of gypsum
Hemihydrate Formula	CaSO₄·½H₂O	Plaster of Paris (β-form)	145.15 g/mol	0.5 water molecules	Partially dehydrated gypsum used in construction
Alpha Hemihydrate Formula	CaSO₄·½H₂O	Dental Plaster (α-form)	145.15 g/mol	0.5 water molecules	High-strength hemihydrate with different crystal structure
Bassanite Formula	CaSO₄·½H₂O	Bassanite	145.15 g/mol	0.5 water molecules	Natural hemihydrate mineral
Selenite Formula	CaSO₄·2H₂O	Selenite	172.17 g/mol	2 water molecules	Transparent crystalline form of gypsum
Alabaster Formula	CaSO₄·2H₂O	Alabaster	172.17 g/mol	2 water molecules	Fine-grained, massive form of gypsum

Chemical Reaction Formulas

Dehydration Reactions

Reaction Type	Chemical Equation	Temperature Range	Application
Partial Dehydration	CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O	120-180°C	Production of Plaster of Paris
Complete Dehydration	CaSO₄·2H₂O → CaSO₄ + 2H₂O	300-400°C	Production of anhydrite
Two-Step Dehydration	CaSO₄·½H₂O → CaSO₄ + ½H₂O	180-300°C	Complete water removal

Hydration Reactions

Reaction Type	Chemical Equation	Process	Time Required
Plaster Setting	CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O	Hardening of plaster	10-30 minutes
Anhydrite Hydration	CaSO₄ + 2H₂O → CaSO₄·2H₂O	Slow natural process	Days to weeks

Solubility Formulas

Parameter	Formula/Value	Conditions	Units
Solubility Product (Ksp)	Ksp = [Ca²⁺][SO₄²⁻]	At 25°C	2.4 × 10⁻⁵
Solubility in Water	2.6 g/L	At 25°C	grams per liter
Solubility Equation	CaSO₄·2H₂O ⇌ Ca²⁺ + SO₄²⁻ + 2H₂O	Equilibrium	-

Percentage Composition Formulas

Component	Formula for % Calculation	Percentage in Gypsum
Calcium (Ca)	(40.08/172.17) × 100	23.28%
Sulfur (S)	(32.07/172.17) × 100	18.62%
Oxygen (O)	(112.00/172.17) × 100	65.07%
Hydrogen (H)	(4.03/172.17) × 100	2.34%
Water Content	(36.03/172.17) × 100	20.93%

Industrial Application Formulas

Application	Formula/Calculation	Purpose	Industry
Cement Retarder	2-5% CaSO₄·2H₂O by weight	Controls setting time	Construction
Soil Amendment	pH = 6.5-7.5 (target range)	Improves soil structure	Agriculture
Paper Filler	10-25% CaSO₄·2H₂O by weight	Increases opacity	Paper Manufacturing

Crystal System and Properties

Property	Formula/Value	Description
Crystal System	Monoclinic	a ≠ b ≠ c, α = γ = 90°, β ≠ 90°
Density Formula	ρ = m/V	2.31-2.33 g/cm³ for gypsum
Hardness (Mohs)	1.5-2.0	Very soft mineral

What is the formula of gypsum?

Best Courses for You

Detailed Solution

courses

Get Expert Academic Guidance – Connect with a Counselor Today!

best study material, now at your finger tips!

download the app

Download the App