Answer to Question #312920 in General Chemistry for Ibrahim

Question

5.92(g) of hydrated Feso4 when heated to a constant mass gave 3.24(g) of anhydrous salt. Calculate the number if moles off water crystallization in the hydrated salt (H=1, O=16, S=32, Fe=52)

Answer 1

Solution:

hydrated FeSO₄ = FeSO₄⋅nH₂O

anhydrous salt = FeSO₄

The molar mass of anhydrous FeSO₄ is (56 + 32 + 16×4) = 152 g/mol

Therefore,

Moles of FeSO₄ = (3.24 g FeSO₄) × (1 mol FeSO₄ / 152 g FeSO₄) = 0.0213 mol FeSO₄

Schematic chemical equation:

FeSO₄⋅nH₂O ⟶ FeSO₄ + nH₂O

According to the principle of mass conservation:

Mass of FeSO₄⋅nH₂O = Mass of FeSO₄ + Mass of H₂O

Therefore,

Mass of H₂O = Mass of FeSO₄⋅nH₂O − Mass of FeSO₄ = 5.92 g − 3.24 g = 2.68 g

The molar mass of water (H₂O) is (1×2 + 16) = 18 g/mol

Therefore,

Moles of H₂O = (2.68 g H₂O) × (1 mol H₂O / 18 g H₂O) = 0.1489 mol H₂O

The mole ratio between FeSO₄ and H₂O in the hydrated salt:

Moles of FeSO₄ : Moles of H₂O = 0.0213 : 0.1489= 1 : 6.99 = 1 : 7

Thus, the formula of the hydrated salt is FeSO₄⋅7H₂O

The number of moles of water crystallization in the hydrated salt is '7'

Answer: The number of moles of water crystallization in the hydrated salt is '7'