1. Learning objective:
WALT: perform titrations using acidified potassium manganate (VII)
WILF: the mass of iron in an iron tablet
15/06/2018
Iron is an essential mineral in the human body – most conspicuously its role in haemoglobin
Most people gain sufficient iron from their diet but some need supplements in the form of iron (II) sulfate (ferrous sulphate)
Titration against acidified potassium manganate (VII) can be used to find the amount of iron (II) (Fe2+) in the tablets

2. The principle
Complete the half equations and combine them to produce an equation for the reaction between iron (II) and manganate (VII)
MnO H+ + 5 e- ⇋ Mn H2O
5 Fe2+ ⇋ 5 Fe e-
MnO H+ + 5 e- + 5 Fe2+
 Mn H2O + 5 Fe e-

3. The method
Weigh five iron tablets, then dissolve them in about 100 cm3 1.0 moldm-3 sulfuric acid in a conical flask – this might require gentle warming
Why minimise the heating?
Why use sulfuric acid?
The outer coating is insoluble so filter the solution into a beaker – rinsing the flask to ensure all of the iron (II) sulfate is transferred
Transfer the solution into a cm3 volumetric flask – rinsing the beaker into volumetric flask and make up to the mark

4. What goes where? Potassium manganate (VII) is very dark
The potassium manganate (VII) is put into the burette:
Advantages: Disadvantages:

5. Method Pipette 25.0 cm3 iron (II) solution into the flask
Add about 25 cm3 sulfuric acid and titrate with 0.01 moldm-3 potassium manganate (VII)
Repeat until you have two concordant titres

6. Calculation Calculate your mean titre to the nearest 0.05 cm3
Calculate the amount of MnO4- added
Calculate the amount of Fe2+ in a 25.0 cm3 sample
Calculate the total amount of Fe2+ in the original tablets
Calculate the mass of:
Iron (Fe)
Iron (II) sulfate FeSO4
Iron (II) sulfate heptahydrate (FeSO4.7H2O)
Which species is used by the manufacturer?

7. For a later lesson… Weigh accurately between 2.5 and 3 g of brass
Place the brass in a 250 ml beaker in the fume cupboard
Add about 20 cm3 concentrated nitric acid and enjoy the show…