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.
----------------------

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.

--

 

[nobahar]

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

Thanks Borek.

 

[DeeNos]

I can provide an explanation for both queries.

1. The concept of sacrificial anodes is used to protect metals from corrosion. In this case, the iron nail is wrapped with zinc, which is more reactive than iron. This means that when the nail is exposed to oxygen and moisture, the zinc will oxidize first, forming a protective layer over the iron. This process is known as galvanization and it helps prevent corrosion of the iron nail. However, it is important to note that corrosion can still occur if the zinc layer is damaged or if the nail is exposed to harsher conditions. So, it is not entirely correct to say that corrosion did not take place in the nail wrapped with zinc, but it is less likely to occur due to the presence of the sacrificial anode.

2. The oxidation number of an element is a measure of the number of electrons it has gained or lost in a chemical reaction. In the case of KMnO4, the overall charge of the compound is 0, so the sum of the oxidation numbers of each element must equal 0. Oxygen (O) is usually assigned an oxidation number of -2, so in this case, 4(-2) = -8. This means that the oxidation number of potassium (K) and manganese (Mn) must add up to +8 in order to balance the overall charge. Since potassium is a Group 1 element, it typically has an oxidation number of +1. Therefore, the remaining +7 oxidation number is assigned to manganese. This is because manganese can have multiple oxidation states, but in KMnO4, it is in its highest oxidation state of +7.