HSC 2012-2015 Chemistry Marathon (archive) (9 Viewers)

[Aysce]

re: HSC Chemistry Marathon Archive

Ah, I see what you were asking.

My bad :/

Yup my mistake. In that case, one of the hydrogen atom's electron is removed and a coordinate covalent bond is made between the oxygen atom and that particular H atom.

Still need some work - how embarrassing.

 

[Sy123]

re: HSC Chemistry Marathon Archive

Ah, I see what you were asking.

My bad :/

Yup my mistake. In that case, one of the hydrogen atom's electron is removed and a coordinate covalent bond is made between the oxygen atom and that particular H atom.

Still need some work - how embarrassing.

Not embarrassing at all tbh. I don't expect many people to get that question anyway.

 

[Aysce]

re: HSC Chemistry Marathon Archive

Not embarrassing at all tbh. I don't expect many people to get that question anyway.

Nah when you cover coordinate covalent bonds, it's rather straight-forward. My mistake here was removing an electron from the unbonded pair which you stated wasn't possible rather than the valence electron of the H atom.

 

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

Hey guys,
I have a questions here:
I did this questions in a past paper but my teacher said I wouldn't get a full mark because my solution has a contradiction...
The question is: Evaluate the suitability and potential of ethanol as a fuel source in terms of its impact on society the environment and identify possible future directions for research. 8 Marks
In the begining I talked about why ethanol is suitable as a fuel etc... then I listed 3 advantages and about 4 disadvantages then the assessment and finally future directions for research.
One of my advantages was:
It is greenhouse neutral i.e. the carbon dioxide ethanol produces is reused in the synthesis of its raw materials, therefore it doesn't contribute to global warming.
Photosynthesis: [equation]
Fermentation of glucose: [equation]
Combustion: [equation]
Theoretically, total number of moles of carbon dioxide emitted is zero.
and then in my disadvantages I said:
Although ethanol is theoretically greenhouse neutral, practically it is not as energy input is required for cultivation of cellulose crops and also distillation of the 15% concentrate ethanol produced, this means CO2 is produced...
Is it really a contradiction? Would I lose marks for it?

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

 

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

Ethylene undergoes polymerisation where its double bonds are opened up with suitable catalysis and conditions, providing extra bonding capacity which is used to bond each monomer, a process called addition polymerisation. The most important product of this process is polyethylene. Polyethylene is one member of a class of polymers known as addition polymers. An addition polymer is a polymer which is formed by an addition reaction; where functional groups on unsaturated monomer units react (the double or triple bonds open out) and the free electrons can be used to covalently bond with neighbouring monomer units in order to form the polymeric chain via rearrangement of bonds without the loss of any atom or molecule.

 

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

Does anyone know if addition polymerisation is faster or slower than condensation? I am getting mixed answers from my notes...

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Does anyone know if addition polymerisation is faster or slower than condensation? I am getting mixed answers from my notes...

I don't believe there is a direct answer to this as it would depend on many factors and in particular, the conditions that are set. As you should know, the conditions (such as catalyst, temperature etc) play an important role in the polymerisation of ethylene and the rate of polymerisation can be altered by varying such variables and so, you can't simply say one is faster than the other.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

Ethylene undergoes polymerisation where its double bonds are opened up with suitable catalysis and conditions, providing extra bonding capacity which is used to bond each monomer, a process called addition polymerisation. The most important product of this process is polyethylene. Polyethylene is one member of a class of polymers known as addition polymers. An addition polymer is a polymer which is formed by an addition reaction; where functional groups on unsaturated monomer units react (the double or triple bonds open out) and the free electrons can be used to covalently bond with neighbouring monomer units in order to form the polymeric chain via rearrangement of bonds without the loss of any atom or molecule.

Great answer! I was looking for "Synthetic addition polymer" haha

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Great answer! I was looking for "Synthetic addition polymer" haha

In terms of HSC, you probably don't need "synthetic" and in fact, you might lose marks for it. William Sidis' answer may get penalised for too much irrelevant information - it was a 2 mark question, an answer would require a few words to a couple of lines at most.

 

[Sy123]

re: HSC Chemistry Marathon Archive

In terms of HSC, you probably don't need "synthetic" and in fact, you might lose marks for it. William Sidis' answer may get penalised for too much irrelevant information - it was a 2 mark question, an answer would require a few words to a couple of lines at most.

Hahaha HSC Chemistry is such a joke

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

In terms of HSC, you probably don't need "synthetic" and in fact, you might lose marks for it. William Sidis' answer may get penalised for too much irrelevant information - it was a 2 mark question, an answer would require a few words to a couple of lines at most.

I don't understand why I would lose marks for writing synthetic, polyethene is not a biopolymer so why cant i write SYNTHETIC? (thats why i put 2 marks for it, otherwise it wouldve been a 1marker)

 

[someth1ng]

re: HSC Chemistry Marathon Archive

I don't understand why I would lose marks for writing synthetic, polyethene is not a biopolymer so why cant i write SYNTHETIC? (thats why i put 2 marks for it, otherwise it wouldve been a 1marker)

Where in the syllabus does it say "synthetic"? If it does, then I will stand corrected but otherwise, it is always a risk to include extra information beyond the HSC in the exam.

 

[nightweaver066]

re: HSC Chemistry Marathon Archive

Where in the syllabus does it say "synthetic"? If it does, then I will stand corrected but otherwise, it is always a risk to include extra information beyond the HSC in the exam.

I don't see a problem unless the extra information is wrong.

Go ahead and add extra information if you like, but just remember that all the marks that can be awarded are given for things in the syllabus.

 

[aekryan]

re: HSC Chemistry Marathon Archive

What is the catalyst used in catalytic cracking?

AND

a) Identify 3 properties of the catalyst that makes it useful
b) Describe 2 of them in relation to catalyst cracking (ie. why is this property useful for cat cracking?)

I'm sorry if it sounds weird, i dont know how to word questions xD

3 properties??? =L
Pouros aluminosilicate (this doesnt really constributte anything to the question and i dont really know what it means but i think its a property). Very fine and (increase surface area) and can thus catalyst the reaction at a faster rate? Lowers the activation energy allowing the process in the cat cracker to be effectuated at 500 degrees instead of 850. idk..

 

[darkfenrir]

re: HSC Chemistry Marathon Archive

Does anyone know if addition polymerisation is faster or slower than condensation? I am getting mixed answers from my notes...

ahh fuck this is right on the tip of my mind yet I CANT THINK OF THE ANSWER lol

I read it only a few days ago and I forgot -_-

 

[someth1ng]

re: HSC Chemistry Marathon Archive

The catalyst used has:
A large surface area allowing more area to accommodate a reaction.
The ability to absorb reactants to weaken their bonds.
Solid means that it can maintain its shape and thus, more likely be reused.

The third one is something I made up but it makes sense to me.

 

[someth1ng]

re: HSC Chemistry Marathon Archive

I don't see a problem unless the extra information is wrong.

Go ahead and add extra information if you like, but just remember that all the marks that can be awarded are given for things in the syllabus.

I lost marks all the time because of it - at school, it's best to stick to the syllabus as different teacher views won't really matter.

 

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

Great answer! I was looking for "Synthetic addition polymer" haha

Yeah, I don't think it is wrong to say it is a synthetic polymer because there are three types of polymers covered in the HSC, natural, bio and synthetic but it is still not wrong not to say synthetic.

 

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

ahh fuck this is right on the tip of my mind yet I CANT THINK OF THE ANSWER lol

I read it only a few days ago and I forgot -_-

I know for sure that addition polymers are faster because multiple chains can form at the same time and then join together in the termination stage but 1 or two of my notes say condensation is faster which got me confused.