Aims and background
Here is another opportunity to practise some of the skills that you may need for your practical skills assessment. In this practical you analyse iron tablets using iron (II)’s ability to lose electrons when titrated with an oxidising agent such as potassium manganate(vii) (potassium permanganate).
The aim is to carry out an ‘assay’ – a testing of the composition of commercially bought iron tablets. Assaying is used extensively in the chemical industry as part of the quality control procedures needed to ensure that high standards are maintained.
■ Eye protection will need to be worn with this experiment as the iron sulfate is harmful.
■ Sulfuric acid is classed as irritant at this concentration.
Equipment and materials
■ Sulfuric acid, 1 mol dm−3, IRRITANT
■ Potassium manganate(vii) solution 0.01 mol dm−3
■ 5 iron tablets
■ Two-place decimal balance
■ Burette (with white markings if possible), clamp and stand
■ Pipette (25 cm3)
■ Pipette filler
■ Teat pipettes
■ White tile
■ Conical flasks (250 cm3)
■ Volumetric flask (250 cm3)
■ Stirring rods
■ Mortar and pestle
■ Weighing boat or bottle
1. Set up the apparatus as shown in the diagram in Figure 1.
2. Rinse out all glassware with distilled water.
3. Rinse out the burette with a small sample of potassium manganate(vii) solution.
4. Using the funnel, fill the burette with potassium manganate(vii) solution, to the 0 cm3 mark, ensuring that no air bubbles are left in the tap and that any spillage is wiped from the sides of the burette.
5. Remove the funnel from the burette before you start titrating.
6. Place the five iron tablets in the mortar and pestle and crush to a fine powder.
7. Weigh the powder and record its mass to two decimal places.
8. Dissolve the powder in about 100 cm3 of sulfuric acid, using gentle heat and stirring.
9. When the solution is fully dissolved (i.e. clear with...