Question

1.567 g of an unknown Mohr’s salt was dissolved in 80 mL of the sulfuric acid / phosphoric acid mixture solution. This iron solution was then titrated with a potassium permanganate solution (0.02M), what will be the volume at the equivalence point for the titration? Show all your calculations including formulas.

Answer 1

The balanced equation is :

2KMnO₄ + 8H₂SO₄ + 10 FeSO₄.(NH₄)₂SO₄.6H₂O K₂SO₄ + 2MnSO₄ + 5Fe₂(SO₄)₃ + 10 (NH₄)₂SO₄ + 48H₂O

Molar mass of Mohr's salt is 284 g/mol

Number of moles of Mohr's salt , n = mass / molar mass

                                                  = 1.567 g / 284(g/mol)

                                                  = 5.52x10^-3 mol

According to the balanced chemical equation ,

10 moles of Mohr's salt reacts with 2 moles of KMnO₄

5.52x10^-3 mol of Mohr's salt reacts with M moles of KMnO₄

M = (2x5.52x10^-3 ) / 10

    = 1.10 x10^-3 mol

Volume of KMnO4 at Equilvalence point , V = number of moles / Molarity

                                                               = (1.10 x10^-3 mol) / 0.02 M

                                                               = 0.055 L

                                                               = 0.0552 x10³ mL                 Since 1 L = 10 ³ mL

                                                               = 55.2 mL