[tortoise]

what the product would be?

[sdekivit]

Fe2O3 i guess.

[Grumples]

Well, there are two oxides of iron: Fe2O3 and Fe3O4.  the first is just common rust, while the latter is called magnetite, a black, magnetic (duh!) substance.  While a rusting piece of iron tends to produce red rust; burning iron, in my experience, creates a product that is much darker; indicating that some magnetite might be formed as well.

[Borek]

Well, there are two oxides of iron: Fe2O3 and Fe3O4.

Not exactly. The two oxides are Fe₂O₃ and FeO. Fe₃O₄ is a mixed oxide, you may treat it as Fe₂O₃^.FeO.

[tortoise]

The high school students who want to enter universities have to pass an important exam called entrance exam to universities in Vietnam. This year, this exam began on 3rd and finished on 10th of July.

In the exam this year, the chemistry exam (Grade A) had this problem:

III. 2. By burning comletely 33,4g the mixture B1 which consists of 3 metals Al, Fe & Cu in the atmosphere, we have 41,4g the mixture B2 which consists of 3 oxides. Then let B2 react comletely with the solution H₂SO₄ 20%, d = 1.14 g/ml.
a) Write all the reaction equations.
b) Find the value of the minimum volume of H₂SO₄ 20% which can mix the B2.

And the solution was given:
3Fe + 2O₂ = Fe₃O₄.

But many students wrote Fe₂O₃. So they had no marks. This cause the protest from both the students and the teachers, but there was nothing new. The teachers of the Education and Training Department kept their solution.

After quoting from many believable books, a university teacher said that:
* 3Fe + 2O₂ = Fe₃O₄ (at 150 - 600⁰C)
   The oxidization continues if O₂ is odd:
   4Fe₃0₄ + O₂ = 6Fe₂O₃ (at 450 - 600⁰C)
* That Fe reacts O₂ produces the mixture: Fe₂O₃ + Fe₃0₄
* Therefore, either Fe₂O₃ or Fe₃O₄ had to be accepted.

[tortoise]

That problem is a "funny" problem   The data given is wrong ! Do you see that?

By culculating carefully, you will have n_Fe = 0.1875 (mol), n_Cu = 0.4 (mol) and n_Al = -0.1 (mol) !
Actually, 27.(-0.1) + 56.(0.1875) + 64.(0.4) = 33.4g = m_B1.

Hey, what do you think?

[tortoise]

5 days has passed .

I am wondering if you don't concern to this matter...