Titration lab with potassium permanganate

[cottonz]

Homework Statement

1.The primary standard in thiss experiment is ammonium iron(II) sulphate hexahydrate, (NH4)2Fe(SO4)2*6H2O. Calculate the number of millimoles of ammonium iron(II) sulphate hexahydrate in a 1.0000g sample.

2.Give the balanced equation for oxidation of iron(II) ion by permanganate and find how many millimoles of permanganate ion react with one millimole of ammonium iron(II) sulphate.

3.Calculate the number of millimoles of permanganate ion that titrates 1.0000g of ammonium iron(II) sulphate.

Homework Equations

The balanced equation for 2 is MnO4^- + 8H^+ + 5Fe^2+ ---> Mn^2+ + 4H20 + 5Fe^3+

The Attempt at a Solution

For #1, would I just use 1.0000g x (1mol/molar mass of ammonium iron(II) sulphate hexahydrate) then change the answer into millimoles. I get 2.5501millimoles

For #2, would I use the moles/millimoles I got for #1 and use the ratio from the equation? But where does the ratio come from if ammonium iron(II) sulphate isn't in the balanced equation?

 

[Borek]

You know how to calculate number of moles of Fe²⁺ per mole of Mohr's salt, but you don't know how to calculate number of moles of Mohr's salt that contain a mole of Fe²⁺? It is the same thing, just the ratio is reversed (which doesn't matter here, as 1/1=1).