Stankovic123's chem q's

[zvezda]

Yes there is. But it took me like 2 hours of searching and reading. I eventually found a good answer in someone's PhD thesis. The answer involves several more things (such as the concept of 'entropy', which is not introduced in VCE), so I don't think I should invoke that level of theory here.

You asked a pretty damn good question I learned a few things while trying to confirm my explanation.

ok fair enough lol.


Anyway, another thing, a possible product of incomplete combustion could be C and H2O yeah? not C2? it only just occurred to be that it is odd that C is on its own without bonding to another C, because isn't that how many non-metallic elements are found (eg. O2, H2, Cl2 etc..)??

[zvezda]

State why incomplete combustion of hydrocarbons is harmful to humans.

Because it produces carbon monoxide which is toxic to humans??? <---- that's what I wrote as an answer but I'm not happy with it. What could you say as an answer to such a question? and btw, could this sort of question possibly come up on an exam?

[teletubbies_95]

You could possibly include , something like it affects proteins in the body , ie. quaternary structured haemoglobin changes due to carbon monoxide , affecting metabolic functions?
i dont know.

[Mao]

Anyway, another thing, a possible product of incomplete combustion could be C and H2O yeah? not C2? it only just occurred to be that it is odd that C is on its own without bonding to another C, because isn't that how many non-metallic elements are found (eg. O2, H2, Cl2 etc..)??

C2 does exist. When you light a fire, the blue part contains some C2. http://en.wikipedia.org/wiki/Diatomic_carbon
However, C2 is very reactive and unstable, we can't get it in reagent form (i.e. in a bottle), at least not easily.

State why incomplete combustion of hydrocarbons is harmful to humans.

Because it produces carbon monoxide which is toxic to humans??? <---- that's what I wrote as an answer but I'm not happy with it. What could you say as an answer to such a question? and btw, could this sort of question possibly come up on an exam?

I don't see anything wrong with this.

But, if you want a more detailed explanation (something you will learn in U4), Hemoglobin (which make up most of red blood cells) transports O2 from lungs to muscle, which are consumed for energy (O2 + glucose --> CO2 + H2O + energy), hemoglobin then transports CO2 from muscle to lungs. CO also binds to hemoglobin in similar ways as O2, but much stronger, as such, CO will deprive the body of O2 and things will start shutting down, and very bad news for the person.

You could possibly include , something like it affects proteins in the body , ie. quaternary structured haemoglobin depletes due to carbon monoxide , affecting metabolic functions?

I don't quite understand this. Structures (primary, secondary, tertiary and quaternary) are properties of proteins, I don't understand how a structure may 'deplete', the structure could change (not by much in the case of hemoglobin) if that's what you mean.

[teletubbies_95]

yesh! Sorry, it was supposed change , due to the carbon monoxide !

[zvezda]

C2 does exist. When you light a fire, the blue part contains some C2. http://en.wikipedia.org/wiki/Diatomic_carbon
However, C2 is very reactive and unstable, we can't get it in reagent form (i.e. in a bottle), at least not easily.
I don't see anything wrong with this.

But, if you want a more detailed explanation (something you will learn in U4), Hemoglobin (which make up most of red blood cells) transports O2 from lungs to muscle, which are consumed for energy (O2 + glucose --> CO2 + H2O + energy), hemoglobin then transports CO2 from muscle to lungs. CO also binds to hemoglobin in similar ways as O2, but much stronger, as such, CO will deprive the body of O2 and things will start shutting down, and very bad news for the person.
I don't quite understand this. Structures (primary, secondary, tertiary and quaternary) are properties of proteins, I don't understand how a structure may 'deplete', the structure could change (not by much in the case of hemoglobin) if that's what you mean.

So how come we generally write the incomplete combustion equations with C only?

[zvezda]

Question:
5.91g of chlorine gas reacts with exactly 2.33g of a pure alkene according to the equation:
CnH2n + Cl2 --> CnH2nCl2
Determine the molecular formula of the alkene.

Now, i figured out the moles of Cl2 and from that, I was able to get the molar mass of the alkene. Then I just used trial and error to get to the answer. BUT, is there another way to do this other than just trial and error? I really dont like trial and error unless I REALLY have to use it

[teletubbies_95]

therefore = 28.04 g/mol- molar mass

So mathematically you could do it like this

CnH2n = 28.04 g/mol-
= (C x n) + ( H x 2n)
= ( 12x n) + (1x 2n)
= 12n+ 2n
= 14n

therefore 14n= 28.04 g/mol-

therefore n=2 and then you can find the rest .

hope that helps!

[Stick]

OK, so this not actually as difficult as it seems, because the word 'alkene' contains some very important information. We know that the empirical formula is CH2 and the molar mass of that empirical formula is 14g/mol.

Now:

n(Cl2)=5.91/71=0.08323943661mol
n(alkene)=0.08323943661mol
M(alkene)=2.33/0.08323943661=27.9915397664g/mol
Molecular formula multiple=27.9915397664/14=1.9993956976 (basically 2)

Therefore the molecular formula of the alkene is C2H4 (ethene).

[zvezda]

far out, didn't think of the empirical formula being CH2, so damn obvious. Didnt think of doing it mathematically like that either.
Cheers guys

[Mao]

So how come we generally write the incomplete combustion equations with C only?

What do you mean? I need some context to answer this.

[zvezda]

What do you mean? I need some context to answer this.

We get the general equation for incomplete combustion of hydrocarbons, and this is what they are:
alkane/alkene + O2 --> CO + H2O      OR
alkane/alkene + O2 --> C + H2O

with the second equation, why wouldn't it be C2 as one of the products?

[Stick]

I think it's because a quadruple covalent bond does not exist (correct me if I'm wrong).

[Mao]

I think it's because a quadruple covalent bond does not exist (correct me if I'm wrong).

C2 doesn't have a quadruple bond. It does not have a completed covalent shell, which is why it is so reactive.

We get the general equation for incomplete combustion of hydrocarbons, and this is what they are:
alkane/alkene + O2 --> CO + H2O      OR
alkane/alkene + O2 --> C + H2O

with the second equation, why wouldn't it be C2 as one of the products?

C2 is an intermediate in the combustion process, we never really get it unless we try very very hard to isolate it. Under typical conditions, C2 always reacts to form other things, so it's not correct to say it's a product. C2 is less stable than elemental C (e.g. coal), and so presumably a lot of these intermediates would group together to give elemental C as a more stable product. (i.e. C2 decays to C)

[zvezda]

C2 doesn't have a quadruple bond. It does not have a completed covalent shell, which is why it is so reactive.

C2 is an intermediate in the combustion process, we never really get it unless we try very very hard to isolate it. Under typical conditions, C2 always reacts to form other things, so it's not correct to say it's a product. C2 is less stable than elemental C (e.g. coal), and so presumably a lot of these intermediates would group together to give elemental C as a more stable product. (i.e. C2 decays to C)

Ah ok, that clears up things. Thanks Mao.

Also, I've come across this molecule:
semistructural formula: CH2C(CH3)COCH3
How would I name this? 2-methylbut-1-ene-3-one???  <---To me that doesn't sound right