A solution of potassium permanganate (KMnO4) will be standardized using solid sa

Question

A solution of potassium permanganate (KMnO4) will be standardized using solid samples of iron(II) ammonium sulfate hexahydrate (Fe(NH4)2(SO4)2•6H2O) called FAS for simplicity. Note that six hydrated water molecules are Part of the total molecule. The net ionic equation for the standardization of the permanganate solution is: ??????4?(????) + 5 ???? 2+(????) + 8 ?? +(????) ? ????2+(????) + 5 ???? 3+(????) + 4??2??(??)

In this equation MnO4 - ions are reduced (charge decreases) to Mn2+ while Fe2+ ions are oxidized (charge increases) to Fe3+ ions. Note that the hydronium ions are supplied by making the solution acidic by adding sulfuric acid in excess to the beaker. This equation also shows that for every mole of permanganate, five moles of iron (II) are required. Thus, from the mass of Fe(NH4)2(SO4)2•6H2O used and from the volume of KMnO4 required for the titration you can calculate the molarity of the KMnO4 solution using stoichiometry.

Standard solid samples FAS. KMnO4 is hygroscopic meaning that water will adsorb to the surface of the solid KMnO4 that was used to create the reagent solution you have before you. Therefore, when the mass of KMnO4 used is recorded, the mass of an unknown quantity of water is also included, meaning any molarity calculations derived from this mass are inaccurate! Therefore, a primary standard that is not hygroscopic

Why was it important and necessary to standardize the permanganate? What was the purpose of the FAS?

Explanation / Answer

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

Permanganate is hygroscopic in nature. So it's concentration changes with time. That's why we have to standardize permanganate to know the exact strength of the solution.

Standard FAS solution can be used as the primary standard to know the exact strength of permanganate solution stoichiometrically.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.