Calculations with equations involving solutions
4 marks · NormalPotassium permanganate reacts with iron(II) sulfate as shown:
Calculate the number of moles of FeSO₄ in 50 cm³ of 0.20 mol/dm³ solution.
Use the equation to find the number of moles of KMnO₄ needed to react with this amount of FeSO₄.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 0.010 mol
(b) 0.002 mol
Common mistakes: Wrong conversion; not using correct ratio 2:10
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Converts volume to dm³ and uses formula.
A1 (a) · 1 mark · 0.01 mol of FeSO₄. (follow-through)
M2 (b) · 1 mark · Uses equation ratio (10 FeSO₄ : 2 KMnO₄ or 5:1). (follow-through)
A2 (b) · 1 mark · 0.002 mol of KMnO₄ correctly calculated. (follow-through)
Worked solution
a) 50 cm³ = 0.05 dm³, so moles FeSO₄ = 0.05 × 0.20 = 0.01 mol.
b) Ratio FeSO₄ : KMnO₄ is 10:2 or 5:1, so moles KMnO₄ = 0.01 ÷ 5 = 0.002 mol.