Understanding metallurgy rxns from Yusuf

Yuvraj Singh...

Dec 23, 2019 06:17

Like if I heat copper pyrite. @YusufHasan

Which contain both iron as well as copper ore.

What will be the best method to purify it?

Yusuf Hasan

Yeah, so the idea is to look at the activity of the metal

Do you know about the electrochemical series?(A rudimentary form of the same known as "reactivity series will also work)

Yuvraj Singh...

Yes.

Yusuf Hasan

Yeah, so you should be aware the copper falls even below hydrogen i.e. it doesn't react with most acids

In the reactivity series^

Yuvraj Singh...

Yes

Yusuf Hasan

It only reacts with oxidising acids like HNO3, at sufficiently high concentration. Hence, we can safely say that the activity of copper is quite less, right?

Yuvraj Singh...

Dec 23, 2019 06:23

Yes.

It is good oxidizing agent compare to hydrogen

@YusufHasan

Yusuf Hasan

So, if you have CuFeS2, can we expect it to directly break down to copper, thus making it pointless to form the complete oxide?

This is expected to happen on a preliminary oxidation basis

SO2, flies off

FeO, slags off with silica

Yuvraj Singh...

Oxidation of iron?

Yusuf Hasan

Of course

Wait

Yuvraj Singh...

OK.

Yusuf Hasan

Suppose you have to guess now the products of the reaction of CuFeS2 + O2

Yuvraj Singh...

Dec 23, 2019 06:26

OK.

Yusuf Hasan

What would be your thinking?

Yuvraj Singh...

Oxidation of iron.

Or copper

Depending upon their oxidizing power.

Yusuf Hasan

Why 'or'? Why not both?

See, if you are reacting O2 itself with CuFeS2

then it obviously means that O2 has good enough oxidising power, cuz it's oxygen itself

Now, O2 as a reagent

I will expect it to oxidise whatever it possibly can

Right now I am not looking for yield

only products

Yuvraj Singh...

OK.

Yusuf Hasan

So, there are three things on the RHS, Cu, Fe and S

which are not in their highest oxidation states

due to the very nature of O2

I will expect all three to react with , and form oxides

with S, the most common oxide is SO2

If an oxide is common, it obviously means it's thermodynamically stable... Hence it's common in the atmosphere, right?

Yuvraj Singh...

Dec 23, 2019 06:32

Yes.

@YusufHasan

Yusuf Hasan

Also, since we know this is a partial roasting reaction, I anyway won't expect SO3 to form because oxidation is being controlled. On a similar logic, I will expect Fe to go to FeO, or Cu to go to it's oxide. Now, how to predict which way it goes?

you look at the OS of Cu and Fe in copper pyrite

Can you tell me what they are?

@YuvrajSingh...

Yuvraj Singh...

+1 and +3

@YusufHasan - 2

Yusuf Hasan

@YuvrajSingh… Yeah cool, so now, the corresponding oxide for Cu is Cu2O

and for iron is Fe2O3

Now, the thing is, I will not expect Cu2O to form

Yuvraj Singh...

OK.

Yusuf Hasan

Reason being is that CuO is always the more preferred oxide for Cu than Cu2O, due to the difference in oxidation states

Yuvraj Singh...

Dec 23, 2019 06:42

OK.

I do not know that, good fact to learn!

Yusuf Hasan

Can you see why?

No, I am not teaching you any facts

I am showing you how to predict inorganic reactions

Yuvraj Singh...

OK, let me think.

Yusuf Hasan

Hint is that, think about the stabilisation by the O2- anion to the lattice form of Cu+ and Cu2+

Yuvraj Singh...

I am not sure is it related to hydration energy.

Or lattice energym

@YusufHasan

Yusuf Hasan

@YuvrajSingh… U tell me. In the reverbatory furnance

Where the reaction occurs, what phase does this reaction occur in?

Yuvraj Singh...

Dec 23, 2019 06:46

Sorry, but as I said to rennie sir too that I couldn't, t understand how it works. @YusufHasan

Yusuf Hasan

All the materials are taken in the liquid state there, and hot air is blown through it

Yuvraj Singh...

OK.

Yusuf Hasan

So mostly, the phases of the products except SO2 is liquid

Yuvraj Singh...

OK.

Yusuf Hasan

But I wasn't asking you to go so far; you can look at this simply by Fajan's rule.

Cu2O has got 2 Cu+ polarising one O2-

Yuvraj Singh...

Dec 23, 2019 06:49

Ah, I missed it. Yes yes.

Yusuf Hasan

and CuO has got one Cu2+ polarising one O2-

right?

Yuvraj Singh...

Yes

Yusuf Hasan

In Cu2O, due to equally powerful polarisation by both Cu+ on one O2-

There will be a chance, where the O2- decides to give one electron to each Cu+ symmetrically

Thus freeing itself of charge, and getting released as nascent oxygen. Nascent oxygen will automatically

dimerize, and form O2

Yuvraj Singh...

symmetrically?

Yusuf Hasan

Like, O2- has got a dinegative charge right?

each negative charge corresponds to one extra electron

Yuvraj Singh...

Dec 23, 2019 06:54

OK.

Yusuf Hasan

So, if two people are trying to pull away electrons equally strongly from O2-

It will give both of them one electron each, get released as nascent O, and instantly dimerize to form O2]

E.N concept?

Yuvraj Singh...

Nothing I was think something else continue.

But it is wrong.

Yes.

Yusuf Hasan

And I never said it's easy for O to give electrons to Cu, I am saying that O2- will try to symmetrically remove charge from it by giving one electron each to Cu+, and thermally break down to Cu and O2

Yuvraj Singh...

Yes yes.

Yusuf Hasan

ofcourse, this breakdown can only occur at high enough temperatures; at room temperature you can find Cu2O easily. But recall the temperature in a reverbatory furnance

Yuvraj Singh...

Dec 23, 2019 06:58

Below than melting point.

Yusuf Hasan

It is pretty high, clearly. So there, Cu2O will obviously not tend to be stable

Yeah, but it's still high enough to start decompositions

for Cu2O

That's why, the reaction plays smart

Yuvraj Singh...

OK. Wow. I understand the logic of prediction.

Can we do same to fe too.

Yusuf Hasan

It doesn't form a copper oxide at all, hence the product from copper's side is simply, copper sulphide

It's also expected in another way

Because, as I stated earlier, this is partial roasting of a copper ore

Yuvraj Singh...

OK.

Yusuf Hasan

So, by the name itself, I can say that the oxidation of copper has been controlled, and any Cu2O formed must have been negligibly small by experimental terms, otherwise why call it partial roasting at all?

Yuvraj Singh...

Dec 23, 2019 07:03

Yes.

Yusuf Hasan

So, again, we end up with copper sulphide

Yuvraj Singh...

Yes.

Yusuf Hasan

Now, we have to think about iron. Since copper wasn't being oxidized, we would expect Fe to be the cation which was oxidized, as an anion(namely S) has already been oxidized to SO2

Also, if you recall the thermite reaction

Fe2O3 + Al gives Al2O3+ Fe

Yuvraj Singh...

Highly exothermic.

Yusuf Hasan

There, we saw that Fe2O3 does exist to a very high temperature in a liquid form, and it wasn't decomposing . It was only that the Al displaced it from the salt solution, otherwise it would have existed like that, in the molten form, without breaking down

Hence, it seems quite reasonable to report Fe2O3 as the product from iron's side.

But, the problem is, Fe2O3 is also a mixed oxide(kinda)

Are you aware of mixed oxides?

Yuvraj Singh...

Dec 23, 2019 07:10

No.

Yusuf Hasan

Well, these are oxides which are postulated to be a mix of different oxides to account for various properties

A simpler example to see is Fe3O4

We say that it's a mix of Fe2O3 and FeO

You can see that from the molecular formula; and this is one idea which helps to sketch out many reactions in inorganic chemistry

as you can write the reaaction of a mixed oxide as a sum of it's constitutents

Fe3O4 is even named as Iron(II,III) oxide

@YuvrajSingh… Are you fine with this?

Yuvraj Singh...

Yes.

Yusuf Hasan

Yeah, so the idea I was referring to was something else actually

As per our normal logic, I wouldn't really report Fe2O3 to exist at quite a higher temperature

From practical experience

We know that Fe2O3 in it's hydrated form, is rust

Yuvraj Singh...

Yes

Yusuf Hasan

And, I am pretty sure that that red powdery thing is not going to sustain temperatures such as those in a reverbatory furnance right?

Yuvraj Singh...

Dec 23, 2019 07:19

Correct.

Yusuf Hasan

So, my other option? FeO

Yuvraj Singh...

Yes.

Yusuf Hasan

Hence, you have successfully predicted the products of the controlled oxidation of CuFeS2 logically

CuFeS2 + 3 O2 → 2 FeO + 2 CuS + 2 SO2

Yuvraj Singh...

Such, deep thinking, but yes it is logically correct one more help if you can?

Yusuf Hasan

Yeah sure

Yuvraj Singh...

Dec 23, 2019 07:22

How do I read ellingham diagram.

Yusuf Hasan

You get this by practice; I can now do such thinking within 1-2 minutes :)

@YuvrajSingh… It's pretty straightforward actually, have you read the NCERT on this topic?

Yuvraj Singh...

I am reading only NCERT for this part.

Yusuf Hasan

The yellow box if I am not wrong, where are you facing difficulty?

Yuvraj Singh...

@YusufHasan correct.

I mean what happen if two delta g graph of two compounds intersect.

Yusuf Hasan

It means they have same stability at that temperature

So, neither of those 2 reactions are more favorable than the other

Ipso facto, either both will occur simultaneously, or none of them will occur and a 3rd side reaction can start

provided that side reaction has more negative delta G than the former 2 reactions

Yuvraj Singh...

Dec 23, 2019 07:27

Cool understand. One more doubt regarding leaching process.

Yusuf Hasan

Yep?

Yuvraj Singh...

What actually leaching mean.

I have read bauxite ore leaching.

Yusuf Hasan

Like...The word, or the process?

Yuvraj Singh...

Process.

Yusuf Hasan

@YuvrajSingh... Yeah, the Bayer process technically

Okay

Yuvraj Singh...

Dec 23, 2019 07:30

Yes. Why do this process what happens what happens after leaching.

Yusuf Hasan

Okay, so see the reason for performing leaching or any concentration process

is to remove most of the impurities, and it would be an added bonus if we could also turn that thing into it's oxide

although the conversion to oxide can be done later also

Now,the concentration process is determined by it's reactivity, and also it's other properties

Yuvraj Singh...

OK.

Yusuf Hasan

Aluminium, as I said, is a high reactivity metal...So any attempt of physical separation will simply lead to more side reactions of the metal with the surroundings

Moreover

Yuvraj Singh...

Ok

Yusuf Hasan

Aluminium's ore bauxite, again due to the high reactivity of aluminium and it's places of occurrence, has a bad habit of picking up various other kinds of oxides as impurities including SiO2, TiO2, iron oxides etc.

Due to magnetic nature of impurities themselves, magnetic separation is out

gravitational separation is risky, because due to such a large sample space of impurities

it's quite likely that there is a type of oxide impurity with similar density as that of bauxite

So that again goes..and froth floatation is only for sulphide ores

3

So, all popular physical separations have failed

Yuvraj Singh...

Dec 23, 2019 07:41

Yes

Yusuf Hasan

We hence had to invent a new method, to obtain the oxide of Al for further extraction, and hence leaching was developed

Yuvraj Singh...

OK.

Yusuf Hasan

Do you have a doubt as to why we are trying to make only oxides of the metal, and not it's sulphides or carbonates will do the job?

Yuvraj Singh...

Actually yes, I was going to ask you that.

@YusufHasan

Yusuf Hasan

It's simple, when a metal oxide reacts with carbon(coal is the most common reducing agent because it's cheap, so factories use it in spades), it produces the metal, and releases CO2(sometimes CO). If I do the same with a sulphide, it will produce the metal, and release CS2

Yuvraj Singh...

Dec 23, 2019 07:47

Yes.

Yusuf Hasan

CS2 is poisonous, CO2 is not(directly) harmful. As a factory owner,if I start using sulphide ores , I can't simply release CS2 into the atmosphere, while I can do that with CO2(provided I do it under regulations)

Yuvraj Singh...

Ah, OK.

Yusuf Hasan

It would become a big headache for me then to either process all the CS2 before releasing, which will cause me a lot of overhead expenses.Or, I can end up even killing my factory workers if it just keeps boiling up inside the factory with no outlet

Also, if you look at formation enthalpies, CO2 has a highly negative one, while CS2 formation enthalpy is positive. Hence, thermodynamically, reaction will drive forward if CO2 is the side product as compared to CS2

Yuvraj Singh...

OK.

Yusuf Hasan

Anything else you wanted me to explain? About the process itself?

Yuvraj Singh...

Dec 23, 2019 07:52

@YusufHasan question not from leaching Because I understand the reaction.

Zone refining.

Yusuf Hasan

Ok, what about it?

@YuvrajSingh...

Yuvraj Singh...

Noble gas atmosphere?

What does that imply.

Yusuf Hasan

You keep an inert gas like argon around the entire setup, so that side reactions are avoided

Yuvraj Singh...

Side reaction like?

@YusufHasan

Yusuf Hasan

Anything, like we are doing very high refining of elements like boron, silicon etc. to make semiconductors, so we would want to avoid any layer of boron oxide or silicon oxide on the surface

which will easily form on contact with air

Yuvraj Singh...

Dec 23, 2019 07:59

OK, I like the way you predicted the product of reactions I am very keen to understand and solve the way you approaches the answer.

@YusufHasan

Yusuf Hasan

@YuvrajSingh… It's something which comes by practice..You need to know the basic classes of reactions, how to break a reaction in smaller known ones...You can keep asking me about whichever reaction you come across, and I can try and show you how to guess the mechanism and products of that reaction

Keep pinging me with reactions till you get the hang of it, I would say :)

Yuvraj Singh...

Thanks you very much, I need one more advice apart from jee what kind of other exams should I give?

Yusuf Hasan

@YuvrajSingh… For entering into engineering, or some other options as well?

Yuvraj Singh...

Both.

Yusuf Hasan

Well, you can give bitsat, viteee, iiith-ugeee. IISER Aptitude Test(IAT), IIM Indore 5 year program entrance,manipal(if you feel like)

Yuvraj Singh...

Dec 23, 2019 08:06

OK, do you know about Institute of Chemical engineering Mumbai.

Yusuf Hasan

Upse I won't recommend because UP doesn't really have great colleges..And yeah I do, it's quite a reputed college

It takes through mains only I guess

Yuvraj Singh...

OK what about jadavpur University.

Wbjee.

Yusuf Hasan

Oh yes forgot about it, WBJEE u should also give, more preference over Manipal and viteee

JU CS is superb

Yuvraj Singh...

OK.

@YusufHasan I have some good inorganic chemistry sheet consist of 40 question, so I want to discuss it with you after completing it, so can I talk to you around 4 o clock.

If you are not busy.

Yusuf Hasan

@YuvrajSingh… Ping me when you wanna start, I will tell you then If I am busy or not(most prolly not busy)

Yuvraj Singh...

Dec 23, 2019 08:13

Cool:) they are quite difficult, they all are asking products.

@YusufHasan

For me at least.

Yusuf Hasan

No problem, we'll try to make it simple :)

Yuvraj Singh...

Thanks I will long you when I am done with them.

♦ Physics.

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