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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: bamster on June 10, 2009, 04:48:42 PM

Title: Mass expressed as Fe2O3 in total sample?
Post by: bamster on June 10, 2009, 04:48:42 PM
I did a lab today using an iron sample solution.
I did a titration and found that it contained 0.089352g of Fe.
The question asks to express the mass as Fe2O[/sub]3[/sub] in total sample?
How do you do this?

This is the equation for the reaction

MnO4-  + 5Fe2+ + 8H+    :rarrow:  Mn2+  + 5Fe3+  + 4H2O

It was a redox reaction for the lab but I don't know if this was it.
I know that to get the total sample is multiply it by 10 because it was a 25ml aliquot in a 250ml sample but i don know how to get it into grams of iron 3 oxide first.
Title: Re: Mass expressed as Fe2O3 in total sample?
Post by: Borek on June 10, 2009, 05:14:11 PM
I am not sure what you are asking about.

You know iron mass - I assume you have calculated it from the stoichiometry of titration.

If you know how to calculate stoichiometry of the titration, you should be also easily able to calculate mass of iron oxide containing given mass of iron - both calculations are based on very similar principles.
Title: Re: Mass expressed as Fe2O3 in total sample?
Post by: bamster on June 10, 2009, 05:18:51 PM
I really dont know how to do this.
Make an equation of adding iron to iron III oxide or something?
Give me a hint or something
Title: Re: Mass expressed as Fe2O3 in total sample?
Post by: Borek on June 10, 2009, 06:02:57 PM
How many moles of P in 1 mole of P2O5?

How many moles of P2O5 contain 1 mole of P?
Title: Re: Mass expressed as Fe2O3 in total sample?
Post by: bamster on June 10, 2009, 06:12:29 PM
Quote from: Borek on June 10, 2009, 06:02:57 PM
How many moles of P in 1 mole of P2O5?

How many moles of P2O5 contain 1 mole of P?

so you multiply it by 2 cause there are 2 Fe's in FeIII oxide?

= 0.089910g x 2
= 0.17982 g x 1000mg x10
=1798.2 mg?

It says to put the answer in milligrams


or is it a 1:1 mole so it is the same mass?
Title: Re: Mass expressed as Fe2O3 in total sample?
Post by: Borek on June 11, 2009, 04:12:08 AM
Quote from: bamster on June 10, 2009, 06:12:29 PM
so you multiply it by 2 cause there are 2 Fe's in FeIII oxide?

No. If you have two atons of Fe, how many Fe2O3 molecules can you make? 1, or 4?

Quote
or is it a 1:1 mole so it is the same mass?

No, it is not 1:1.

Seems like you have a terrible gaps in you stoichiometry knowledge.
Title: Re: Mass expressed as Fe2O3 in total sample?
Post by: bamster on June 11, 2009, 07:47:51 PM
Quote from: Borek on June 11, 2009, 04:12:08 AM
Quote from: bamster on June 10, 2009, 06:12:29 PM
so you multiply it by 2 cause there are 2 Fe's in FeIII oxide?

No. If you have two atons of Fe, how many Fe2O3 molecules can you make? 1, or 4?

Quote
or is it a 1:1 mole so it is the same mass?

No, it is not 1:1.

Seems like you have a terrible gaps in you stoichiometry knowledge.


multiply grams of fe by 1:2 ratio and then multiply by molar mass of Iron III oxide over molar mass of Fe.