[sharbeldam]

Can someone explain what happens in this experiment?
We have 3 agar plates with K3Fe(CN)6 solution and phenolphtalein.
In the first plate we put an iron nail and close it.
In the second one we put an iron nail wrapped in magnesium
in the third one we put an iron nail wrapped in Copper.

Now we need to expect when do we get a blue color and when we get a blue color.

My try:
We get a red color when Fe+2 gets oxidized by o2.
We get a blue color when we produce Fe[Fe(CN)6]2 which is a result of Fe+3 reacting with K3Fe(CN)6.
Another thing I know is that magnesium protects iron from being oxidized more than copper.

But My question is when do we get blue color at all? how does iron turn into Fe+3 in this experiment? for instance in the closed first plate, will it dissolve into Fe+2 or Fe+3 or stay Fe(s)?

Please give me a tip.
Thanks!

[chenbeier]

Magnesium protects, copper accelerates. The other one is in the middle. No, slight blue, dark blue is the ranking.

[sharbeldam]

Thank you but when Fe loses electrons, it becomes Fe+3 or Fe+2 ?
because blue color would appear only if it becomes the ferric ion. the red color would appear if it was ferrous ion.

[chenbeier]

First you get Fe²⁺ later if oxidation takes place you get Fe³⁺.

[sharbeldam]

Sorry if im being dense but, what exactly ionizes it? for instance the iron nail in the agar/solution without Cu/Mg, it will stay Fe or turn into which ion it will turn.
it needs to become Fe+2 or Fe+3 before reacting with O2/Potassium Ferricyanide.

TY

[chenbeier]

It will go first Fe => Fe²⁺+ 2 e^-,
The second reaction is Fe²⁺ => Fe³⁺ + e^- accelerated by O₂

Mg < Fe < Cu

Copper drives to corrod iron. Iron itself drives to corrod magnesium. It goes from nobel to innoble.

[sharbeldam]

So does that mean I will get Fe+3 ions in all three plates except the one with magnesium since its protecting the iron metal? and if that is the case then Fe+3 will react with Potassium Ferricyanide to give me blue color.

It's just that it is stated that the plates that will have only Fe+2 ions, will turn red, and the plate with Fe+3 ions will turn blue and the third one wont change color...

[chenbeier]

No opposite. Fe2+ react with Fe(CN)₆^3- blue

Or Fe³⁺ and  Fe(CN)₆^4- gives blue

[sharbeldam]

Ok so apparently they have it wrong, this makes more sense.
So please correct me if im wrong.

First plate-> I dont have any metals except Iron, it will turn into Fe+2 (Because there is water there but not much oxygen), and then Fe+2 will react with oxygen to produce red color (rust). but wouldnt it also produce blue color for reacting with Fe(CN)6 ion?

Second plate-> It has magnesium around the iron, so iron becomes Fe+2 but it doesnt react with oxygen so it becomes blue because of the reaction with Fe(CN)6.

Third plate-> it becomes red fast.

[chenbeier]

No,

Iron alone get blue
Iron and magnesium, no reaction
Iron an copper more strong blue,later maybe red

[sharbeldam]

I really appreciate your answers, but I'd love a full correction as in, what was wrong in what I said.
In the first plate, it would turn blue because I dont have enough oxygen since its closed so it would react with the Fe(CN6) ion to turn blue?

In the second plate, i understand that Fe would not react with O2 since Mg is protecting it, but does that mean it stays Fe and Will not turn into Fe+2 at all and react with Fe(CN6) ion?

Does Fe only ionize when it reacts with O2? I read that it can turn into Fe+2 when you it touches water/solution or is that only because the water has O2(aq)?

[chenbeier]

Iron get oxidised, if get wet. The ironhexacyanidoferrate-III is an Indicator for determing iron-II.
Iron change from 0 to 2+ and 3+.
Ironhexacyanidoferrate-II is an Indicator for determing iron-III.