Redox Titrations (OCR)

24.3 cm³ of 0.0200 mol dm^-3 KMnO₄ reacted with 20.0 cm³ of an iron(II) solution in the presence of sulfuric acid. Calculate the concentration of the iron(II) ion.

Ratio MnO₄^-:Fe²⁺ is 1:5

• 0.122 mol dm^-3

• 0.0243 mol dm^-3

3.00 g of a lawn sand containing an iron(II) salt was shaken with dilute H₂SO₄. The resulting solution required 25.00 cm³ of 0.0200 mol dm^-3 potassium manganate(VII) to oxidise the Fe²⁺ ions in the solution to Fe³⁺ ions. Use this to calculate the percentage by mass of Fe²⁺ ions in this sample of lawn sand.

Ratio MnO₄^-: Fe²⁺ is 1:5

• 4.65%

• 0.93%

Calculate x in the formula FeSO₄.xH₂O from the following data: 12.18 g of iron(II) sulfate crystals were made up to 500 cm³ acidified with sulfuric acid in a volumetric flask. 25.0 cm³ of this solution required 43.85 cm³ of 0.0100 mol dm^-3 KMnO₄ for complete oxidation.

Ratio MnO₄^- : Fe²⁺ is 1:5

• 7

• 69

• 300

• 6.5

A tablet with mass 0.940 g was dissolved in dilute sulfuric acid made up to 250 cm³ with water. 25.0 cm³ of this solution was titrated with 0.00133 mol dm^-3 KMnO₄ requiring 32.5 cm³ of the KMnO₄. Calculate the percentage by mass of Fe²⁺ in the tablet.

Ratio MnO₄^- : Fe²⁺ is 1:5

• 12.8%

• 2.57%

• 1.28%

• 25.7%

13.2 g of iron(III) alum were dissolved in water and reduced to an iron(II) ion solution by zinc and dilute sulfuric acid. The mixture was filtered and the filtrate and washings made up to 500 cm³ in a standard volumetric flask. 20.0 cm³ of this solution required 26.5 cm³ of 0.0100 mol dm^-3 KMnO₄ for oxidation. Calculate the percentage by mass of iron in iron alum.

Ratio MnO₄^- : Fe²⁺ is 1:5

• 14.0%

• 2.8%

• 0.56%