Titrations 1 ~ KMnO4 + Ammonium Iron (II) Sulfate

Standardising KMnO4 Solution

• read from top of meniscus

• Standard solution: Ammonium iron (II) sulfate

• Indicator: none

• 1st lot of H2SO4: when making up ammonium iron (II) sulfate

• Use of 1st lot: prevent atmospheric oxygen oxidising Fe2+ to Fe3+

• 2nd lot: added to conical flask immediately before titration

• Use of 2nd lot: a) ensure reaction goes to completion b) prevent formation of brown participate of MnO2

• End point: solution turns permanent pink

• Type of catalysis: autocatalysis

MnO4- + 5Fe2+ + 8H+ = Mn2+ + 5Fe3+ + 4H2O

Finding Amount of Iron in Iron Tablet

• Crush tablets using mortar and pestle

• Indicator: none

• Standard solution: KMnO4

• Add 1st lot of HSO4 to stop atmospheric oxygen oxidising Fe2+ to Fe3+

• Add 2nd lot of HSO4 to ensure reaction goes to completion + prevent formation of brown precipitate

• End point: solution turns permanent pink

5Fe2+ + MnO4- + 8H+ = 5Fe3+ + Mn2+ + 4H2O