Redox Titration Calculations

2S₂O₃^2– (aq) + I₂(aq) ==> S₄O₆^2– (aq) + 2I^– (aq)

25.0 cm³ of a solution of iodine in potassium iodide solution required 26.5 cm³ of 0.0950 mol dm^–3 sodium thiosulphate solution to titrate the iodine.

What is the concentration of iodine to 3s.f?

Tags

NGSS.HS-PS1-7

1.51 g of the wire was dissolved in excess of dilute sulphuric acid and the solution made up to 250 cm³ in a standard graduated flask.

A 25.0cm³ sample of this solution was pipetted into a conical flask and needed 25.45 cm³ of 0.0200 mol dm^–3 KMnO₄ for complete oxidation.

MnO₄^- : 5Fe²⁺

Calculate the percentage of iron in a sample of steel wire to 3s.f.

8.25g of an iron(II) salt was dissolved in 250 cm³ of pure water. 25.0 cm³ samples were pipetted from this stock solution and titrated with 0.0200 mol dm^–3 potassium manganate(VII) solution. The titration value obtained was 23.87 cm³ . Remember MnO₄^- : 5Fe²⁺

Guided steps:

Calculate the moles of manganate(VII) used in the titration.

Calculate the moles of iron(II) ion titrated

Calculate the mass of iron(II) titrated

Calculate the total mass of iron in the original sample of the iron(II) salt.

Calculate the % iron in the salt and enter the numbers to 3s.f below

2.83 g of a sample of haematite iron ore [iron (III) oxide, Fe₂O₃] were dissolved in concentrated hydrochloric acid and the solution diluted to 250 cm³. 25.0 cm³ of this solution was reduced with tin(II) chloride (which is oxidised to Sn⁴⁺ in the process) to form a solution of iron(II) ions. This solution of iron(II) ions required 26.4 cm³ of a 0.0200 mol dm^–3 potassium dichromate(VI) solution for complete oxidation back to iron(III) ions.

Sn²⁺ + 2Fe³⁺ ==> Sn⁴⁺ + 2Fe²⁺

Cr₂O₇^2– + 14H⁺ + 6Fe²⁺ ==> 2Cr³⁺ + 6Fe³⁺ + 7H₂O

Calculate the percentage of iron(III) oxide in the ore to 3s.f.

10.0 g of iron(II) ammonium sulphate crystals were made up to 250 cm³ of acidified aqueous solution. 25.0 cm³ of this solution required 21.25 cm³ of 0.0200 mol dm^–3 potassium dichromate(VI) for oxidation.

Calculate x in the formula FeSO₄.(NH₄)₂SO₄.xH₂O

Ratio 6Fe²⁺: Cr₂O₇^2–

Step 1: calculate moles of potassium dichromate(VI) (Cr₂O₇^2–)

Step 2: calculate moles of Fe²⁺ in 25cm³ using the above ratio

Step 3: calculate moles of Fe²⁺ in 250cm³

Step 4: Moles of Fe²⁺ = moles of FeSO₄.(NH₄)₂SO₄.xH₂O. Therefore use the moles of Fe²⁺ and the mass of crystals given to you at the start to work out the Mr of FeSO₄.(NH₄)₂SO₄.xH₂O

Step 5: subtract the Mr of all the known atoms, leaving you with xH₂O. Divide this by 18 to find x!

Tags

NGSS.HS-PS1-2