abdullahAK
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#1
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Hello.
Q:
Why potassium iodide (KI) reaction with Iron (III) sulfate produces Iodine.
But Potassium iodine reaction with iron(II) sulfate does not .
Help will be appreciated.
Thanks.
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stimtothesky
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In the question did you get given electrode potential data? Sounds like one of those questions where you have to use the data to explain it.
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Interea
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If no further information is given I can only guess that it wants something to do with redox: I- is oxidised to I2, which of Fe3+ and Fe2+ can be easily reduced?
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abdullahAK
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@ Interea the question screenshot is below.
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Bangz
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I don't know what you are asking. It tells you why in the qs. It says fe2+ is a reducing agent and fe3+ in an oxidising agent. Using oxidation and knowledge of colours of transition metals is all you need to answer the qs.
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Bangz
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If you just wanna know for extra knowledge it would be electrode potentials. FeSO4 isn't a strong enough reducing agent aka its E isn't negative enough.
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abdullahAK
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Let me explain you what exactly I'm asking.
If you look at the question's screenshot it has one potassium iodide row which asks what will happen if it is added to iron(II) and iron (III) aqueous solutions. Now, the mark scheme says by adding it in iron(III) aqueous solution, Iodine is one of the products formed.However, Iodine does not form when it potassium iodide reacts with Fe(III) solution.
Why is it so?
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anon-21
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Hi, can I ask where you got this question from? what exam board is it?
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abdullahAK
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Yeah sure, it is IGCSE CIE past paper question.
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Bangz
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You mean the other way around. KI with Fe(III)SO4 to produce iodine.

Lemme break it down for you. But I bet you'll be kicking yourself as this is real simple.

This is KI with Fe(III)SO4. We are told that Fe3+ ions are oxiding agents. This means the take electrons away. OILRIG. In KI we have I- ions as this is an ionic compound. Taking the electron away leaves us with a standard I. I does not exist alone but in diatomical form so we have I2, aka iodine.

This is KI with Fe(II)SO4. We are told that Fe2+ ions are are reducing agents. This means they give electrons away. To for I2 we need to take electrons away.

Sorry we thought you were alevel thats why we talking electrode potentials. Ask anymore question, if this didn't make sense.


(Original post by abdullahAK)
Let me explain you what exactly I'm asking.
If you look at the question's screenshot it has one potassium iodide row which asks what will happen if it is added to iron(II) and iron (III) aqueous solutions. Now, the mark scheme says by adding it in iron(III) aqueous solution, Iodine is one of the products formed.However, Iodine does not form when it potassium iodide reacts with Fe(III) solution.
Why is it so?
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abdullahAK
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No problem.
Thanks for the explanation.
But Yes,I have one more question.When we react KI with Fe+2 does it form Potassium.
Last edited by abdullahAK; 8 months ago
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Bangz
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No it will for K+ Ions in the solution
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