Molar Mass of FeSO4·7H2O (Ferrous Sulfate Heptahydrate)

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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 FeSO4·7H2O?

Answer

M(FeSO4·7H2O) ≈
278.01 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.

7 H2O — water of crystallization, part of the molar mass: 7 × 18.015 = 126.105.

FeSO4·7H2O = FeSO4 + 7 H2O → Fe 1, S 1, O 11, H 14

Contribution of each element
Element Atoms, n Atomic weight, A n × A, g/mol Mass fraction, w
Feiron155.84555.845 w ≈ 20.09%
Ssulfur132.0632.06 w ≈ 11.53%
Ooxygen1115.999175.989 w ≈ 63.30%
Hhydrogen141.008014.1120 w ≈ 5.08%
Σ = 278.006 ≈ 278.01 g/mol w = 100%

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

Mass fractions of the elements

Fe 20.09%S 11.53%H 5.08%

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Molar masses of substances nearby

FormulaM, g/mol
PbCO₃ (lead carbonate)267.2
HgCl₂ (mercuric chloride)271.49
Ag₂CO₃ (silver carbonate)275.75
FeSO₄·7H₂O (ferrous sulfate heptahydrate)278.01
PbCl₂ (lead chloride)278.1
MgI₂ (magnesium iodide)278.11
C₁₈H₃₄O₂ (oleic acid)282.468

FAQ

What is the molar mass of FeSO4·7H2O?

M(FeSO₄·7H₂O) ≈ 278.01 g/mol

Is the water counted in FeSO₄·7H₂O?

Yes: the water of crystallization is part of the formula and of the molar mass. 7 H₂O add 7 × 18.015 = 126.105 g/mol; M(FeSO₄·7H₂O) ≈ 278.01 g/mol, while anhydrous M(FeSO₄) ≈ 151.90 g/mol.

How many grams are in 2 moles of FeSO₄·7H₂O?

m = n × M = 2 mol × 278.01 g/mol = 556.02 g.

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