Molar Mass of CaSO4·2H2O (Calcium Sulfate Dihydrate)

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Chemical formula Write symbols with a capital letter: CoCl2 is cobalt chloride, COCl2 is phosgene. A hydrate takes a dot: CuSO4·5H2O or CuSO4.5H2O

What is the molar mass of CaSO4·2H2O?

Answer

M(CaSO4·2H2O) ≈
172.16 g/mol

Atomic weights: IUPAC standard values (CIAAW, 2024); the sum is rounded to the decimal places of the least precise one — S: 32.06.

2 H2O — water of crystallization, part of the molar mass: 2 × 18.015 = 36.030.

CaSO4·2H2O = CaSO4 + 2 H2O → Ca 1, S 1, O 6, H 4

Contribution of each element
Element Atoms, n Atomic weight, A n × A, g/mol Mass fraction, w
Cacalcium140.07840.078 w ≈ 23.28%
Ssulfur132.0632.06 w ≈ 18.62%
Ooxygen615.99995.994 w ≈ 55.76%
Hhydrogen41.00804.0320 w ≈ 2.34%
Σ = 172.164 ≈ 172.16 g/mol w = 100%

Atomic weights: CIAAW, Abridged Standard Atomic Weights (2024)

Mass fractions of the elements

Ca 23.28%S 18.62%H 2.34%

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Molar masses of substances nearby

FormulaM, g/mol
AgNO₃ (silver nitrate)169.87
Ba(OH)₂ (barium hydroxide)171.34
CeO₂ (cerium(IV) oxide)172.12
CaSO₄·2H₂O (calcium sulfate dihydrate)172.16
Yb (ytterbium)173.05
C₆H₇NO₃S (sulfanilic acid)173.19
K₂HPO₄ (dibasic potassium phosphate)174.174

FAQ

What is the molar mass of CaSO4·2H2O?

M(CaSO₄·2H₂O) ≈ 172.16 g/mol

Is the water counted in CaSO₄·2H₂O?

Yes: the water of crystallization is part of the formula and of the molar mass. 2 H₂O add 2 × 18.015 = 36.030 g/mol; M(CaSO₄·2H₂O) ≈ 172.16 g/mol, while anhydrous M(CaSO₄) ≈ 136.13 g/mol.

How many grams are in 2 moles of CaSO₄·2H₂O?

m = n × M = 2 mol × 172.16 g/mol = 344.32 g.

See Also