HSC 2012-2015 Chemistry Marathon (archive) (8 Viewers)

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

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..

I think the proper name for the catalyst is "zeolite- porous crystalline aluminosilicate"

It is true that the catalyst lowers the energy required from 850 to 500 but but catalytic cracking cannot decompose large alkanes into ethylene completely so it is insufficient and thermal cracking is required so should you mention this? Is it related to the catalyst?

Thickett textbook (jacaranda chem) explains this very well (it is the best textbook IMO but extremely detailed):
1) The many cavities and channels inside the porous catalyst provide a high internal surface area for reaction.
2) Lower temperature (about 500ºC) can then be used and this produces considerable savings in energy.
3) Hydrogen atoms are removed from the hydrocarbons onto the catalyst’s surface. The positive hydrocarbon ion that forms undergoes further reactions leading to the formation of the final products.

 

[someth1ng]

re: HSC Chemistry Marathon Archive

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.

I don't know whose notes but as I said, it depends on the conditions. In the right conditions, addition polymerisation is probably faster.

 

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

I don't know whose notes but as I said, it depends on the conditions. In the right conditions, addition polymerisation is probably faster.

Yeah, I just looked at all the notes and none of them say it is slower. I don't know where I got that from lol.
But as you said, if both reactions are at "standard" conditions addition is probably faster.

By the way, what are you going to major in for the science degree? I know that if you do Advanced Science alone you can do two majors like chemistry and physics but if you do a combined degree can you still do two majors for science or only one?

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Yeah, I just looked at all the notes and none of them say it is slower. I don't know where I got that from lol.
But as you said, if both reactions are at "standard" conditions addition is probably faster.

By the way, what are you going to major in for the science degree? I know that if you do Advanced Science alone you can do two majors like chemistry and physics but if you do a combined degree can you still do two majors for science or only one?

You can still do two majors - they will consist of Chemistry and something else - probably Statistics (for big job prospects).

 

[Sy123]

re: HSC Chemistry Marathon Archive

Find the pH of a 10L solution of HCl that contains 1x10^-8 mol of HCl in it

C=n/V

C=1x10^-9

Therefore pH = 9

BUT, this can't be the case HCl is acidic and hence the real pH is really close to 7.

So why doesn't the mathematics work? This isn't an actual marathon question, just curiosity.

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Find the pH of a 10L solution of HCl that contains 1x10^-8 mol of HCl in it

C=n/V

C=1x10^-9

Therefore pH = 9

BUT, this can't be the case HCl is acidic and hence the real pH is really close to 7.

So why doesn't the mathematics work? This isn't an actual marathon question, just curiosity.

You need to take into consideration that water, by itself, released hydrogen ions. In this case, the auto-ionisation of water is significant as it actually produces more hydrogen ions than that of the HCl.

Therefore, the actual pH is closer to -log[10^-9+10^-7] - it's a bit off as that's not the ideal way of calculating it but for HSC's sake, that would be acceptable.

 

[Sy123]

re: HSC Chemistry Marathon Archive

You need to take into consideration that water, by itself, released hydrogen ions. In this case, the auto-ionisation of water is significant as it actually produces more hydrogen ions than that of the HCl.

Therefore, the actual pH is closer to -log[10^-9+10^-7] - it's a bit off as that's not the ideal way of calculating it but for HSC's sake, that would be acceptable.

Alright I see
Thanks

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

Here is one simple question:



For the systematic name of polystyrene, I would like to see 2 names

 

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

Common: polyethylene Systematics: polyethene
Common: poly(vinyl chloride) Systematics: poly(1-chloroethene)
Common: polystyrene Systematics: poly(ethenylbenzene) or poly(phenylethene)

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

Common: polyethylene Systematics: polyethene
Common: poly(vinyl chloride) Systematics: poly(1-chloroethene)
Common: polystyrene Systematics: poly(ethenylbenzene) or poly(phenylethene)

Good job! the "1-" in front of chloroethene is unecessary

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Good job! the "1-" in front of chloroethene is unecessary

It would probably be counted as wrong if you had the "1-".

 

[Sy123]

re: HSC Chemistry Marathon Archive





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[malek123]

Re: HSC 2012 Chemistry Marathon

whats four different heavy matels in water

 

[someth1ng]

Re: HSC 2012 Chemistry Marathon

whats four different heavy matels in water

Crap question - nuff said.

Lead, mercury, zinc and cadmium.

 

[Sy123]

re: HSC Chemistry Marathon Archive

 

[bleakarcher]

re: HSC Chemistry Marathon Archive

Assess the evidence which indicates increases in the concentrations of sulfur and nitrogen oxides in the atmosphere.

 

[girlworld_club]

re: HSC Chemistry Marathon Archive

You need to take into consideration that water, by itself, released hydrogen ions. In this case, the auto-ionisation of water is significant as it actually produces more hydrogen ions than that of the HCl.

Therefore, the actual pH is closer to -log[10^-9+10^-7] - it's a bit off as that's not the ideal way of calculating it but for HSC's sake, that would be acceptable.

Saying that Water released H+ ions due to self-ionisation. Shouldn't it also produce a comparable amount of OH- as well?

 

[albertcamus]

Re: HSC 2012 Chemistry Marathon

A- Citric acid

Analyse the relationship between the position of elements on the periodic table, and the acid-base behaviours of their oxides.

An oxide's acid-base behaviour is dependent upon the metallic character of its element.

The left hand side of the periodic table consists of basic oxides, which are mostly metallic oxides. These basic oxides react with acids to form a salt and water in a neutralisation reaction, as shown in the reaction of some group I and group II metals:





As you move across towards the middle of the periodic table, amphoteric oxides are present, which can act as acidic oxides and basic oxides. An example of this is Aluminium, which can be neutralised by an acid when acting as a basic oxide:



Being amphoteric, aluminium can also act as an acidic oxide, and can thus be neutralised by a base:



Moving towards the right hand side of the periodic table, as elements become less metallic due to their propensity to gain electrons and not lose them, acidic oxides can be found, which are generally non-metals. These react with bases to form a salt and water in a neutralisation reaction:


Will finish later tomorrow sleepy atm

 

[Lieutenant_21]

re: HSC Chemistry Marathon Archive

Anyone has 2012 multiple choice solutions (for phys as well if possible)?

 

[nightweaver066]

re: HSC Chemistry Marathon Archive

Anyone has 2012 multiple choice solutions (for phys as well if possible)?

Chemistry MC answers:
1. B
2. D
3. A
4. C
5. B
6. C
7. D
8. D
9. B
10. B
11. B
12. D(?)
13. D
14. A
15. C
16. A
17. C
18. C
19. A
20. A

Unsure about 12, the rest are 100% correct.