Ammonium iron(II) sulfate crystals have the following formula: (NH₄)₂SO₄·FeSO₄· n H₂O. In an experiment to find n, 8.492 g of the salt were dissolved and made up to 250 cm³ solution with distilled water and dilute sulfuric acid in a volumetric flask. A 25.0 cm³ portion of the solution was titrated against 0.0150 mol dm⁻³ KMnO₄, 22.65 cm³ being required. Calculate n.