[T]

Hello,

The question is:

Fe²⁺ reacts in a 5:1 molar with a solution containing KMnO4^- and dilute sulfuric acid. What is the reaction equation? Omit spectator ions.

So firstly the spectator ion is K+ so omit that. However, I don't understand what the sulfuric acid is doing? Is it a catalyst or something else? Thank you.

(mod edit to title, sjb)

[DrCMS]

Hint - acids are a source of what ions?

Also your question title is misleading try to give better descriptions of the question such as "Iron (II) and Potassium permanganate reaction?"


(mod edit to title, sjb)

[T]

Ok, will try to make better titles from now on (could a moderator tell me what the original title was so I can see the difference?); acids are a source of hydronium ions. So it could bond with the permanganate, forming HMnO₄. Thanks DrCMS

[sjb]

Ok, will try to make better titles from now on (could a moderator tell me what the original title was so I can see the difference?)

I forget exactly, but it was something like "Find the element"

[Hunter2]

The point is still not found. Hint redox reaction.

[T]

I see.

For the redox reaction:
Fe²⁺  Fe³⁺ + e^-

I am not sure about the reduction of MnO₄^-

MnO₄^- + 5e^- + 8H⁺ 4H₂O + Mn²⁺?

Thanks

[Hunter2]

Everything is correct.

[T]

I see thanks. However what does the dilute sulfuric acid do?

[Hunter2]

I think this you should answer yourself now. Look the redox reaction. What happens to the H⁺.

[T]

I see. So if I had NaOH instead of sulfuric acid the permaganate wont react with the iron?

[Hunter2]

In case of alcaline conditions also it will react. But instead of Mn²⁺ MnO₂ will be formed. In this case water reacts: H₂O + (O) + 2 e^- => 2 OH^-

(O) is the oxygen in the oxidieser here Permanganate

Iron will also precipitate as Fe(OH)₂ which is sensitive to oxygen and easily convert to Fe(OH)₃

[Borek]

In the alkaline solutions permanganate gets reduced to manganate, MnO₂ is produced closer to the pH 7.

This is just a rule of thumb though, sometimes you will get a mixture of products.

[Hunter2]

This is in my opinion right, if no reducing agent is present. In present of reducing agent (maybe iron-II is not the best on), like Sulfite, Oxalate, etc. Manganaese dioxide will be formed. This will also happen with Manganate -VI and Manganate -V