[Shing]

The mineral magnetite, Fe3O4, is a mixed oxide containing both Fe(II) and Fe(III).
What is the ratio of Fe(II) to Fe(III) in this mineral?
a) Fe(II) : Fe(III) = 3 : 1
b) Fe(II) : Fe(III) = 3 : 2
c) Fe(II) : Fe(III) = 2 : 1
d) Fe(II) : Fe(III) = 1 : 1
e) Fe(II) : Fe(III) = 1 : 2

I dont know, how to find out the ratio with the amount of information given. You dont have to solve this question, just give me some clue as to how I could know the percentage of Fe (II) and Fe (III) only using the periodic table.

Yelpp!!

[macman104]

Do you know what the oxidation state of oxygen will be?  You can calculate how much total "positive" oxidation state you will need to make the compound neutral (there is no charge on it).  Only one of those answers is correct for that.

[Shing]

Do you know what the oxidation state of oxygen will be?  You can calculate how much total "positive" oxidation state you will need to make the compound neutral (there is no charge on it).  Only one of those answers is correct for that.

Ok, since the oxidation # of O is -2 and there are 4 O's total charge of O is -8
The compound is neutral so Fe3 will have total charge of +8.
I Think Fe (II) has oxidation # of +2, so when i divide +8 by 3, i get 2.666666 so i'm guessing it gonna be 2:1.

not sure, but this is what i think.

[macman104]

Ok, since the oxidation # of O is -2 and there are 4 O's total charge of O is -8
The compound is neutral so Fe3 will have total charge of +8.
I Think Fe (II) has oxidation # of +2, so when i divide +8 by 3, i get 2.666666 so i'm guessing it gonna be 2:1.

Close!  Correct, O is -2, and you have a total charge of -8.

And yes, since the compound is neutral, the sum of the oxidation states on the 3 Fe atoms must equal +8.  The roman numerals indicate oxidation states in transition metals that have more than one oxidation state (like Fe!).  So, Fe(II) is a +2, and Fe(III) is a +3.

All that is left is simple math.  Either check each answer to see if it equals +8.
Or make a list of possible ratios and see which one is in the answer set.

Or, if you want to be really mathy about it, solve this set of equations:

2x + 3y = 8
x + y = 3

x is the number of Fe(II) atoms in Fe3O4 and y is the number of Fe(III) atoms in Fe3O4.  So 2*x (because +2 oxidation state) plus 3*y (+3 oxidation state) = a total of +8, and then there are only 3 Fe atoms.

[Shing]

Ok, since the oxidation # of O is -2 and there are 4 O's total charge of O is -8
The compound is neutral so Fe3 will have total charge of +8.
I Think Fe (II) has oxidation # of +2, so when i divide +8 by 3, i get 2.666666 so i'm guessing it gonna be 2:1.

Close!  Correct, O is -2, and you have a total charge of -8.

And yes, since the compound is neutral, the sum of the oxidation states on the 3 Fe atoms must equal +8.  The roman numerals indicate oxidation states in transition metals that have more than one oxidation state (like Fe!).  So, Fe(II) is a +2, and Fe(III) is a +3.

All that is left is simple math.  Either check each answer to see if it equals +8.
Or make a list of possible ratios and see which one is in the answer set.

Or, if you want to be really mathy about it, solve this set of equations:

2x + 3y = 8
x + y = 3

x is the number of Fe(II) atoms in Fe3O4 and y is the number of Fe(III) atoms in Fe3O4.  So 2*x (because +2 oxidation state) plus 3*y (+3 oxidation state) = a total of +8, and then there are only 3 Fe atoms.

so 1:2.
Thanks for the help. I completely overlooked the fact the the roman numerals were the oxidation states.
Thank you.

[Donaldson Tan]

Fe₃O₄ = Fe₂O₃.FeO