A-LevelChemistryAnalytical techniquesMay/June 2021Paper 5 Q216 Marks
A student is given 250.0 cm³ of solution containing a mixture of Fe2+ and Fe3+ ions. The student is asked to find the total mass of iron ions and the percentage by mass of Fe3+ in the solution by performing titrations with aqueous potassium manganate(VII), KMnO4. The student is told that the Fe3+(aq) ions can be reduced to Fe2+(aq) ions by reaction with zinc. The student is given the following instructions. : Calculate the mass of KMnO4 needed to make 500.0 cm³ of 0.0200 mol dm⁻³ KMnO4(aq). Record the mass of an empty plastic weighing boat (a small container used to hold solid samples). Add the calculated mass of KMnO4 to the weighing boat. Transfer the KMnO4 from the weighing boat into a 100 cm³ beaker. • Add 50 cm³ of distilled water to the beaker. • Transfer the mixture from the beaker into a 500.0 cm³ volumetric flask. • Make up to the graduation mark, dropwise, with distilled water.
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