Chemistry lab problem

[Pereira]

Hello,

Any help will be appreciated.

 

Q:Determine moles of dichromate ion that reacted with iron(II) in titration (use average volume).

 

 

My A: 0.0119mol

 

6 Fe2+ + Cr2O72- + 14 H3O+ 6 Fe3+ + 2 Cr3+ + 21 H2O

 

4g-Fe2+

 

4g*(1mol/558.845g/mol) = 0.0716 moles of Fe

 

(6/0.0716)=1/x

x=(0.0716)1/(6)

 

x=0.0119mols of dichromate.

 

My questions are:

1) am I way off in my approach?

2)Why does the question want me to use volume?

 

It seems that it should not be this easy so I assume I am way off. Also the avg volume of Fe solution 6.75mL and the concentration was =0.102mo/L.

 

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Alright before I submit this thread to publish I tried another approach:

 

molarity(Cr2O7 2-)= (molarity of Fe(II)/6)*(volume of Fe(II)/volume of Cr2O7)

=[(0.102mol/L)/6)] * (0.00675L/0.005L)

=0.017*1.35

=0.2295

 

m(Cr2O72-)=215.992 * .1L *0.2295

m=4.95mols

 

*this answer seems like I am more on the right track I think

 

Are either of these very close. Any hints will be greatly appreciated.

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Edited November 2, 2011 by Pereira

[Pereira]

Recently have gotten a tutor, mods can delete this thread if you want.