Sacrificial Anodes and Oxidation Number of KMnO4

[Procrastinate]

1. I have a question regarding an iron nail wrapped with zinc. The question asks me "Is it correct to say that corrosion did not take place in the nail wrapped with zinc? Explain."

I am not sure whether this is correct but I know that that zinc is more reactive than iron and will thus be more likely to oxidise than iron. However, as it is more likely, there will be some iron which will oxidise since not all of the iron has been cloaked by the zinc.
Is this correct and best explanation? I am not absolutely sure.
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2. KMnO4. O = -2 but how would I figure out what K and Mn is then? Apparently K is +1 and Mn is +7 but I don't know why. Could anyone please explain? I know they have to add up to zero.

 

[nobahar]

KMnO4. O = -2 but how would I figure out what K and Mn is then? Apparently K is +1 and Mn is +7 but I don't know why. Could anyone please explain? I know they have to add up to zero.

Manganate has variable oxidation states, and it's dependent on the environment it's in. Potassium, as you said, has an oxidation state of +1; which I assume you are just expected to know. I again assume the same applies to Oxygen, its oxidation state is invariably -2. From these constants, you can deduce the oxidation state of Manganate.

Discalimer: I can not be held accountable for the accuracy of this post. Someone more knowledgeable will hopefully verify, or correct, as appropriate.

 

[Borek]

I can not be held accountable for the accuracy of this post. Someone more knowledgeable will hopefully verify, or correct, as appropriate.

You are in general right, although in some compounds oxygen is not -2. But as a first approximation -2 is OK.

More on oxidation numbers calculation.

Please note that oxidation numbers are just an accounting device, they don't reflect any measurable property of atoms.

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[nobahar]

You are in general right, although in some compounds oxygen is not -2. But as a first approximation -2 is OK.

Thanks Borek.