Iron metal reacts with oxygen problem

In summary, the discussion is about a chemical reaction in which iron metal reacts with oxygen to produce a mixture of FeO and Fe2O3. The question is to calculate the amounts of FeO and Fe2O3 formed when 20.00 g iron and 11.20 g oxygen gas are reacted, resulting in 3.24 g oxygen remaining. The solution manual presents a different approach, treating each reaction separately and balancing equations to find the amounts of FeO and Fe2O3 produced. The discrepancy between the two methods arises from the assumption that FeO and Fe2O3 are produced in equimolar quantities, which is not necessarily true. Treating each reaction separately eliminates this issue.
  • #1
skepticwulf
74
1

Homework Statement


When the supply of oxygen is limited, iron metal reacts with
oxygen to produce a mixture of FeO and Fe2O3. In a certain
experiment, 20.00 g iron metal was reacted with 11.20 g oxygen
gas. After the experiment, the iron was totally consumed,
and 3.24 g oxygen gas remained. Calculate the amounts of
FeO and Fe2O3 formed in this experiment.

Homework Equations

The Attempt at a Solution


3 Fe + 2 O2 ------> FeO + Fe2O3
20g 0,12mol 0,12mol
0,36mol

As each 3 mol Fe produces 1 mol FeO and Fe2O3 , just by multplying moles to their molar masses it gives:
8,64g FeO and 19,2g Fe2O3. In my solution no need for O2 in calculations.
But, solution manual disagrees :(
Firts of all it states each reaction separately (WHY?)
Then it calculates O2's mole by subtracting 3.24 from 11.2 and by dividing it to its molar mass and then:
"
Let’s assume x moles of Fe reacts to form x moles of FeO. Then 0.3581 – x, the remaining
moles of Fe, reacts to form Fe2O3. Balancing the two equations in terms of x:... " etc etc
But why?? What's wrong with my calculation? I assumed when it says "3.24 g oxygen gas remained" as O2 is surplus, excess.
Did I assume wrong?
 
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  • #2
Besides, if 3 mole Fe react with 2 mol O2 then 0,36 mol react with 0,24 mol and that's 7,68g, so (11,2-7,68), that 3,24g is indeed excess amount. Right?
 
  • #3
skepticwulf said:
3 Fe + 2 O2 ------> FeO + Fe2O3

Why do you assume FeO and Fe2O3 are produced in equimolar quantities? They don't have to and they are not guaranteed to. Just because there are several reaction occurring doesn't mean they can be described by a single reaction equation. Quite the opposite - each process is separate.

Please note your reaction - being actually a sum of two reactions - is not unique. It can be balanced in infinitely many ways, for example

13Fe + 9O2 → 3FeO + 5Fe2O3

or

35Fe + 23O2 -> 13FeO + 11Fe2O3

and so on (check these are indeed correctly balanced). With many "correct" reaction equations, which one are you going to select to solve the question? You won't have this problem if you treat each reaction separately.
 
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Related to Iron metal reacts with oxygen problem

1. What is the chemical equation for the reaction between iron metal and oxygen?

The chemical equation for this reaction is:
Iron (Fe) + Oxygen (O2) → Iron Oxide (Fe2O3)

2. How does the reaction between iron metal and oxygen occur?

The reaction between iron metal and oxygen occurs through a process called oxidation, where iron atoms lose electrons to oxygen atoms. This results in the formation of iron oxide.

3. What are the physical properties of iron oxide?

Iron oxide is a reddish-brown solid that is insoluble in water. It has a high melting point and is a good conductor of electricity.

4. How does the reaction between iron metal and oxygen affect the properties of iron?

The reaction between iron metal and oxygen forms a layer of iron oxide on the surface of the iron, which is commonly known as rust. This layer can weaken the structural integrity of iron and make it more brittle.

5. Can the reaction between iron metal and oxygen be prevented?

Yes, the reaction between iron metal and oxygen can be prevented by using protective coatings, such as paint, to prevent oxygen from coming into contact with the iron. Additionally, keeping iron objects dry and using anti-corrosion products can also help prevent this reaction.

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